Posted on

Dust extractor maintenance is often forgotten

This post is about dust extractor maintenance. It’s very easy to buy a dust extractor and forget about it. They are simple machines, but problems can grow slowly, so suction declines without you noticing.

Turning plastic

Not long ago, I made some wheels out of a commercial cutting board, one of the thick ones used in restaurants or on deli counters. I cut some squares from it with the bandsaw with no problems at all. I put each one in my self-centring engineering chuck and turned it to size and shape. A flat bit in the drill press made the holes in the middle. Back on the lathe mounted on a wooden mandrel to complete the turning. Job done. The plastic material, that I think may be polypropylene, turned very easily with a negative rake scraper, leaving a smooth, shiny surface off the tool. The only problem was the shavings. Long ribbons of plastic wound round the chuck, the mandrel and everything else, with the loose ends flailing as the lathe went round. So although there was no dust, I put the dust extractor on.

Later, it seemed to me that suction at the extractor inlet was not as good as it once was, so I cleaned the filter cartridge. This was a job I had meant to do for some time. There was lots of fine dust in it, blocking the pleated filter. I took it outdoors and used a brush and compressed air to get as much dust as possible out. I put it all back together and switched on. Much better!

Dust extractor fan guard

But was the suction yet good enough? Perhaps there was a blockage somewhere. My extractor is a cyclone unit, and at the outlet of the fan housing there is a grid to stop people putting their hand in and touching the spinning fan. I dismantled the ducting close to the housing to check it. Sure enough, plastic ribbon had blocked the grid. It was surprising that air could get through it at all. The long ribbons went right through the cyclone.

I knew what to look for, because once before when re-configuring the ductwork, I found the remains of a plastic carrier bag blocking the grid. Like the bag, the bird’s nest of ribbon was easy enough to remove. But this time I did my risk assessment and decided that although the grid removed one risk, it created another. The first risk was negligible to anyone with any sense, while the second was significant. So the grid had to go. I removed it, put the ducting back together and switched on. Now the suction is back to what it ought to be.

These are not the only times I’ve come across this problem. It’s possible for long splinters or other objects to get stuck at a bend so shavings build up, or for debris to accumulate at a low spot. And filters clog up from time to time. But often the drop in suction goes unnoticed, even if there is a vacuum gauge to check it.

So my recommendation is to make a point of scheduling maintenance, and to check suction at your dust extractor often. Whether you remove the safety grid is up to you. It also highlights the advantage of an objective way to measure suction. I shall have to consider a vacuum gauge.

Posted on

A centre finder that is easy to make and quick to use can speed up production.

One kind of centre finder on the market has a slot for a pencil to mark intersecting diagonals. These work well on squared timber, but are a bit slow to use on a batch of items. Another kind has a blade. You position the blank, tap it so the blade makes a diagonal line, then repeat. I’ve found that this type can easily start splits in the wood, and needs the end of the blank cut square.
Pencil block centre finderThe centre finder I used for a long time is simply a small wooden block. It has a hole drilled that is a push fit for a short bit of pencil. The hole is off centre. By turning the block on different sides there is some height adjustment. To use it, I put the spindle blank and the pencil block on a flat surface and mark a line across the end of the blank. Then I flip the blank 90 degrees and repeat to do all four sides. The result is a small square marked on the end of the blank, from which I can easily find the centre by eye. This is not super-accurate, but good enough for most purposes, and it is quick. I have several blocks in different sizes so I can pick the one most suited to the size of the spindle blank. The blank need not be square and the pencil block can mark cylinders equally well. The point of a nail works too, and stays sharp.
adjustable centre finder
Deluxe adjustable centre finder

I’ve now made a deluxe adjustable version of the pencil block, with a pivoting arm to hold the pencil. The hole for the pencil has a slot through it and a pinch bolt to lock it.

chuck insert marks the centre of a square or round blank
Chuck insert centre finder

When part of the spindle is to stay square after turning, I need a more exact centre  For this I made a cylindrical insert for a four jaw chuck. I use engineering jaws in my chuck, but any self-centring chuck should work. The insert is a snug fit in the body of the chuck and has a steel point inserted. The centre mark left in the insert after turning it to size gives the place for the point. To use this centre finder, I put the chuck and insert on the bench and adjust the jaws to a loose fit on the blank. Then I insert the end of the blank, twist it slightly to align it, and give it a tap. The steel point marks the exact centre nicely. A batch of same-size blanks are done in no time. The blank must be square to use this method.

To find the centre of a disc or square, I usually use a hardboard disc of proper size. I have a lot of these in different sizes for marking out bowl blanks, and each has a small hole in the middle. I just lay one on the blank, and place it quite accurately by eye or touch. Then I mark the centre with a pencil through the hole.
Posted on

The skew chisel. Learn to use it and see what it can do.

Lots of woodturners fear the skew chisel. They dig in alarmingly, seemingly without any warning or provocation. Some don’t use one at all. But can you really call yourself a woodturner if you can’t use a skew chisel? It’s perhaps  the most useful tool of the lot for spindle turning, so it is worth persevering with it. Just watch Woodturner21’s videos on YouTube to see what the tool is capable of.
You probably already have some idea of how to use the skew chisel for cutting beads and planing a cylinder. You can find the basic principles in turning books and DVDs and I don’t mean to repeat them. All I can tell you is what you already know – that you need lots of practice – and show you how to get the most from that.

Tuning up

First, tune up your skew chisel. Although you can use different grinds, the default has a skew angle of about 70 degrees and a bevel length of about 1.5 times the thickness of the tool. A long bevel makes it easier to see what you are doing, though can make the chisel cut in deeper when you get a catch. Make sure the edge and the points are really sharp, and not rounded over.
A long bevel and straight cutting edge are easier for sharpening on an oil stone or diamond hone. It is OK to use either a straight edge or a curved one straight from a grinder. Try the edge on your thumbnail – if the edge or the point slides without biting in, it’s blunt. Make sure you keep the chisel sharp all the time you are using it, but grind away the sharpness from the long side edges of the tool so they slide easily on the tool rest.
If possible, use a strong, rigid skew of about 10mm square to practice beads (dealers sell these as ‘beading and parting tools’. They are easily ground to a skew angle), and one about 18mm wide for planing. Of course other sizes work perfectly well. But a short edge gives less scope for catching on a bead while cutting on the point, and a wider tool helps keep the long point clear on a cylinder.
Now check your tool rest. Make sure it is smooth. Rub it with a bit of wax to cut friction. Set it a little higher than for gouge cutting. This puts the skew’s handle in a more convenient place for you.

Set up the lathe

Have the lathe running slowly so you can see what is happening at the point of cut, and you don’t feel threatened by the spinning wood. Later you will probably want to use higher speeds. Put on your face shield, just in case.
If you are nervous, use a conical fixed centre (one without any teeth) in the headstock and a revolving one in the tailstock. Make a pilot hole about 6-8 mm wide and deep in the headstock end of the blank. The cone centre will give friction drive only, with nothing else forcing the wood round, and is safer than holding the wood in a chuck. You can adjust the tailstock until the friction is strong enough to drive the blank but it will stop turning if you cut too deep or have a bad dig-in.
Practice on soft timber.  Start with a blank you have roughed down into a cylinder of about 40mm diameter and about 150mm long. You may find bigger pieces intimidating, and long thin ones whippy, neither of which is helpful. Choose a blank that is straight-grained and without knots.

Practice

 Don’t try to make any specific item at first, just keep making beads and planing cylinders. Make beads of about 12-18 mm wide. Use a parting tool first to make a clear space either side of each bead for the chisel to work in.
Use the short point of the skew chisel for cutting beads, although it is possible to use the long point or the edge. Stick with the short point until you are happy with it – later you will try the long point and may end up preferring it. I think the short point is easier to start for many people.
The first few times, use a scraper to make a semicircular bead shape that you can then follow with the skew. The scraper seems easier, but don’t be tempted to keep on with it. When you see the difference in the surface the skew makes, you will understand why. Then, with the lathe switched off, present the skew to that rounded surface, first at the top and then moving down to the bottom of the curve, keeping the point in the proper cutting position as you go. The chisel will begin almost flat on the rest, and end on its side. See how you have to move the tool to keep the point in the right place. Repeat the movements round the curve, so your body begins to learn the action.
Although you will be cutting with the point, the bevel must float (not press) on the cut surface to support the tool. Twist the skew as you go round the curve to keep the point in the cutting position. The edge will be close to the wood, but don’t let it touch. If it touches when the lathe is spinning you might get a catch. When rolling the bead with the edge, the movements are slightly different.

Make a cut

When you are ready, switch on and take a cut. Go slowly so you can see what is happening. No rush. As slow as you like, if using a high speed steel chisel. Carbon steel can overheat if kept in the cut too long. Take a thin shaving. Steer the point all the way round the curve, repeating the movements you started to learn earlier. Try for a smooth, even cut and don’t put pressure on the wood.
Pay attention to the handle movements. They are what you are practicing. As you try to go round the curve, you may have a tendency to complete the movements either too early or too late. Either will make a poorly shaped bead.

Repeat

Don’t work too long on one bead, cutting too deep into the wood, because if the blank gets thin it will start to vibrate and could snap. Start a new one. You may find one side of the bead easier than the other. Concentrate on the easy side first, making half beads, until you understand the process and feel ready to change over. When you get a catch, start again on a fresh part of the blank. This is because the damage can interfere with the free movement of the skew.

Planing cuts 

Planing uses the edge of the skew chisel. Keep the long point up, clear of the wood. Have the cutting edge at about 45 degrees to the lathe axis, because that gives a slicing cut with the shaving coming off near the short point. The key is to keep the bevel floating, without pressure, on the freshly planed surface. It’s easy to let the handle lift a little, and immediately you will get problems.
At first sign of trouble, lay the handle lower. Feel for the position in which the cutting is smooth and quiet and easy. If the handle is too low, the edge just lifts out of the wood, so does no harm. As long as you long pay attention to keeping the long point clear of the wood, you should not get digs when planing. At the ends of the blank, let the cut run off the wood, not onto it, as there will be no bevel support at that point
When you can plane a cylinder without problems, you can try steering the cut to round over the end – this is another good way to make beads.
Posted on

A ball cutting jig is not hard to make if you can find an old machine slide.

Turning a sphere freehand will test your skill, particularly if you need two the same size. If you want more than one or two and don’t want to do them freehand, you can use a simple homemade or commercial ball cutting jig. I make lots of balls in a range of sizes, and for me an effective jig that lets me produce them quickly and accurately is essential.
A ball cutting jig is not hard to make. The most basic is simply a clamp to hold a cutting tool, with a pivot to allow the tool to swing through a quarter circle or more, all fixed to the lathe bed.  The cutting tool is sometimes adjusted in the clamp, or there could be a sliding adjustment so the clamp itself moves. But every commercial ball cutting jig I have seen is a bit flimsy or lacks easy adjustments. The cutter is usually advanced by pushing it forward by hand. Sometimes there is no adjustable stop to control the finished ball size.
I made a heavy-duty ball cutting jig. It does a very good job cutting balls and can also make hemispherical hollows. It was easy to make, but would not have been so easy if it was not based on scrap parts. The key part is a machine slide such as top slide from a metal turning lathe. These can sometimes be obtained from dealers in old tools, or from Ebay. Mine has a rack and pinion lever feed. This is ideal because it is fast to use, but screw feed would be fine. I made the rest of the ball cutting jig from bits of scrap steel. The construction details depend on what machine slide you have so I can’t give more than guidance. Assembly would probably only involve drilling, tapping and bolting together.
Jig set up for use
If you would like to make a ball cutting jig like this but have never done any work with mild steel before, don’t worry. Think of the steel as like very hard wood. You can cut it with a hacksaw, or if it is too thick, drill a line of holes close together and saw through them. Drill the holes with a twist bit in a drill press because it is difficult to drill freehand, even with a power drill. You can cut screw threads in it with a tap by screwing it into the correct size hole.
The ball cutting jig (see outline plan below) consists of the following components, starting at the bottom and working up:
  • A clamping plate that will hold the jig to the lathe bed, allowing it to slide and lock
  • A locating block that fits the lathe bed so the jig can slide along parallel to the bed without sideways movement. This makes locating the pivot point with reference to the ball centre much easier as you can just slide the jig along to the right place. You have to make sure the centre of rotation of the jig passes directly and accurately under the turning axis of the lathe. The short bed on my Graduate lathe has a slot that is offset a little, so I offset the jig to match. The locating block is not load bearing, it just positions the jig before locking down, so wood would do.
  • Next is a pivot block sitting on the lathe bed. Make it thin, but rigid. The thinner it is, the more clearance space you have and the larger the ball you can make. A steel disc about 10 mm thick and 100 mm across would be ideal. Mine is much thicker, because that is the scrap that I had at the time.
  • A rigid slide support platform sits on the pivot block. The mating surfaces of the pivot block and the slide support platform are the pivoting plane. The ideal for the support platform would be a strip of steel of width to suit the slide, and 12 mm thick. If the strip is too short it limits the ball size unnecessarily. I rounded the end of the support platform to clear the headstock.
  • The clamping plate, guide block, pivot block and slide platform are all locked together with the pivot pin. The ideal pin would be a 12 mm or larger steel rod, threaded where necessary. Firmly anchor it in the pivot block. You could screw it into a tapped hole in the pivot block and secure it with thread lock compound. This provides two separate clamping actions – one from below to lock the jig to the lathe bed and another from above to adjust the swivel tension.
  • The pin passes down through clearance holes in the guide block and clamping block. This allows a nut and washer to pull the pivot block down on the lathe bed, positioned by the guide block and held by the clamping block. Above the pivot block, the pin passes through a snug-fitting clearance hole in the slide platform.
  • Above that are a washer and two nuts that lock against each other to set the pivot tension. The pin should preferably be plain where it passes through the slide platform. This is a bearing surface for the pivoting movement. But even a screw thread should give adequate guidance, assuming the hole is a snug fit. The top of the pin needs to have its centre marked to set it exactly beneath the centre of the ball when in use. I turned a point on mine. If the ball turning jig is not lined up properly, the ball it makes will not be perfectly round.
  • Bolt the machine slide to the slide support.
  • The moving slide carries the tool holder. The tool holder on mine came from another old machine, but you could make a similar one by bolting three bits of steel together. It stands on a raising block to bring the tool to the lathe centre height. Having it a little low allows you to use different cutters, with shims. If the cutter is not on centre height, the ball will not be spherical.
  • You need an adjustable stop for the slide movement. How you do this will depend entirely on what slide and other parts you have. I used a bit of threaded rod with two adjustable lock nuts, passing through a clearance hole in a bit of metal attached to the slide. The cut stops when the metal contacts the adjusting nuts. By counting movement of the nut flats, I can adjust the cutting depth and size of the ball very accurately.
lock nuts limit the cut
The lock nuts act as a stop to the slide travel
The largest size of ball you can make depends on the clearance above the top of the swivel point and the travel of the slide. If you make a ball from a cylindrical blank, the clearance needed is more than the radius of the ball. Even more so if you use a square blank, And you have to allow for projection of the cutter.
Tool holder for the jig
The raised tool holder allows you to make a larger ball
To use the ball turning jig, position the swivel axis directly beneath what will be the centre of the ball. I normally make hemispheres with the blank held on a screw chuck, so position the swivel pin beneath the face of the chuck. I glue the hemispheres together to make perfect spheres. Advance the cutting bit, an ordinary round-nosed scraper. Using the slide, pull it round to make a cut, then advance again for the next cut. When set up, I can quickly make lots of identical half balls.
Hemisphere cut with jig
A small hemisphere quickly made in mdf
A ball cutting jig of this kind cannot make a whole ball in one pass. You must hold the blank in the lathe, so the cutter cannot reach all the surface. It could make most of the ball for finishing off by hand. Or you could move the ball in a chuck so the cutter reaches the uncut parts. If you hold the blank in a chuck the cutter could do 75% or more of the circumference in one pass. It would leave just a single chucking spigot. If you hold the blank between centres, it leaves two smaller spigots.
A traditional way of hand turning spheres is to put the roughed out ball between two female cone centres. The spigots project sideways for turning off. Using this same method, you could finish the ball with the jig. It should leave a perfect ball if set up correctly.

Cross-section of ball turning jig

Cross section of ball cutting jig
Posted on

Graduate lathe, a great machine for bowls, though not without faults.

The Graduate lathe was designed in consultation with Frank Pain, one of the first turners to write for the amateur. He was a professional of very long experience and knew a thing or two about lathes and woodturning.

I bought my Graduate lathe many years ago. At the time it had little competition. It was perhaps the most solidly built machine available for non-industrial use, and the lathe you bought if you wanted the best. It was intended primarily for use in schools, back when schools taught woodwork, although my own first turning experience at school was on a Myford. Ray Key, another well known turner, described the Graduate as being ‘head and shoulders above the rest’.

This lathe comes in a long bed and a short bed format. Mine is a short bed, better for bowls and boxes because it takes a larger diameter and you can stand in front of the work without bending. It is not very convenient for spindles, and the maximum workpiece length is short. I have now bought a larger machine, but happily used this lathe for bowls and any larger work. It was a great improvement over the small spindle lathe that I owned at the time.

One problem with the Graduate lathe is that its centre height is low. Most people would want to raise the height. I had a welded triangular platform standing on steel pillars made for mine. This brought the centres up to elbow height, which is the normal standard. It also increased the footprint a little, making it more stable. I have not found it necessary to bolt the machine to the floor.

It came with a 3/4 horsepower motor and 4 pulley speeds with a range from 425 to 2250 rpm. This was not suitable for the large discs that I later began making for globe stands, which needed more power and a lower speed. I therefore upgraded with a bigger motor and a Variturn variable speed drive and had a special large steel faceplate made for these jobs. This goes on the left hand end of the spindle and allowed me to turn discs of over a metre in diameter. I installed the Variturn kit myself. It’s a great addition, quiet and smooth, but the lathe still lacks power for very large work. It copes with large bowls, but I prefer a 2 or 3 HP motor to let me work faster.

Although the Graduate lathe was a great machine in its day, and performed very well for most of my work, it has some weaknesses. The shortbed version seems to have been a design afterthought. For all its good points, its design leads to some problems.

The strange tailstock causes some problems. It is not used on the long bed machine. I didn’t often use the tailstock, so the problems I describe below rarely caused much inconvenience in practice.

The curve of the tailstock casting increases the distance between the centres. It is partly hollow. This causes lack of rigidity, and you can sometimes see it flexing as the work turns. The tailstock position sometimes falls where the two bed slots join at right angles to each other. In this position it is not properly supported. Both the foot of the casting and the locking plate below the bed are too small to bridge the slots at this point – an obvious flaw. You can see this in the photo below. I used an extra-large washer below the bed to help bridge the gap.

Graduate lathe, short bed version
The short bed, with crossed slots for the tool rest holder and strange tailstock

The curved casting has its foot closer to the headstock casting than its centre point. This means that when you want the point close to the headstock the locking lever below the bed will not turn. The headstock casting obstructs it. This means that you can’t always give a shallow bowl blank on a faceplate tailstock support. You can’t pin a disc against a faceplate with the tailstock.

The tailstock ram is just a screw (hollow, to take a No. 2 Morse taper) with a cross hole for a tommy bar to advance and retract. I made a winding handle to use instead of a tommy bar. The alignment of the screw on my lathe is not good. The upper part of the tailstock twists in the casting. A pin locks it, and there is enough play to throw the centre slightly out of true.

The toolrest holder casting is also curved and hollow, as shown in the photo. You can mount it in either of the two slots in the bed, with the same problem at the point where the slots meet. I find however that it is normally set in the cross slot clear of the junction. When the tailstock is in place, the feet of the two castings and their locking levers below the bed can sometimes get in each other’s way.

The tool rest holder also lacks rigidity to some extent. The foot of the casting is not directly under the tool rest stem, which allows slight flexing. The holder can slide along the bed slots and swivel, which ought to give free movement of the rest. But as it swivels, there are times when you cannot put the rest in the right position. and the toolrest locking handle, which is another tommy bar, can foul a large workpiece. With the tailstock removed, which is how I usually have it, the toolrest holder has more freedom of movement and there is rarely a problem in practice. The rests themselves are excellent for faceplate work – rigid, and with a good slope and narrow top. They are not so good for spindle work if you like an underhand grip with a finger behind the rest.

The headstock consists of a single iron casting from floor level up. The shell is heavy and robust, with a thin wall. Bolts attach the cantilevered beds to it.

The lathe came with an outboard bowl turning bed on the left of the headstock. But the inner and outer beds are the same height, so there is no more capacity when using the left hand bed on the short bed model. You cannot use the tailstock outboard. The spindle rotation originally was fixed (now reversible with the Variturn), so the threads are different and accessories aren’t interchangeable. Turning on the outboard side is in the reverse direction to the normal anticlockwise. Left-handed turners might like this. It can make some cuts easier, for example when hollowing bowls.

The outboard spindle thread is the opposite hand to the inner side. Because of this, if you reverse the rotation, the chuck is likely to unscrew. But the outboard bed is at least a convenient handle when moving the lathe. It would be useful for large diameter work when attached to the long bed lathe.

With the inboard bed removed, you can turn large pieces inboard. The limiting factor is when the headstock casting gets in the way. It bulges out half way down to accommodate the motor. Without the bed, a free-standing toolrest is essential. With the left hand bed removed, you can turn even larger pieces outboard. I have used my Graduate lathe to turn built-up oak discs of 60 x 1100 mm. The lack of power was a problem though. The beds come off easily by removing the fixing bolts. There are dowels to align the beds accurately when replacing them. One person can do this with the help of a temporary wooden prop to help support the weight during this process, which can be done by one person. Some people set up a disc sander on the outboard side. The bed is then useful to carry the sanding table.

Conclusion

No lathe is perfect. The Graduate lathe in its short bed version is in some ways a poorly designed and under-powered machine. But because of its mostly great build quality the lathe performs very well and can do excellent work. You may sometimes come up against its eccentricities. But it is usually a delight to use and a Graduate lathe is still a good buy. It’s far superior to most of the cheap lathes on sale now. I used mine for many years and was always able to find a way to overcome its limitations. I have never used the long bed version, which has a more traditional toolrest support and tailstock. It should be excellent for spindle work, though limited for bowl turning.

 

Posted on

Choosing a lathe for woodturning

It’s easy to get it wrong when choosing a lathe. That can greatly restrict the work you can do, or prevent you enjoying woodturning, the very thing you are buying it for. There are so many machines on the market, some of such poor quality that they can only be used for very light work. How do you choose between them?

To perform well, a lathe must be designed well and made well. Top quality doesn’t come cheap, but even inexpensive machines can be compared when choosing a lathe to see which is the better buy. Good quality lathes last indefinitely and often a used one is a better choice than a poor quality new one, even if you have to replace bearings or scrape off a bit of rust or change the motor from three phase to single phase.

Few suppliers advertise that their lathes are of poor quality, so you have to make up your own mind which is best. You can consult other turners, but when you are choosing a lathe, it’s your money. The best approach is to make sure you understand what makes a good machine. When you have examined lathes from different price ranges you will see the differences and be able to make an informed choice.

The perfect lathe  does not exist, and never will, because so much of the design of a lathe involves compromises. For example,  a short bed lathe takes up less space and is easier to use, but will limit the length you can turn. Nor is there such a thing as a beginner’s lathe or starter lathe. Either a lathe is a good one or it isn’t, and a beginner is not well served by a poor quality machine that causes problems in use. You can compromise on size or variable speed if cost is important. But don’t compromise more than you have to on build quality. Weak components and poor manufacturing tolerances may make the lathe almost unusable for anything but very light work.

Here is a checklist.

Size

The first thing to consider when choosing a lathe is size. A big lathe is the most versatile, as although you can do small work on a large machine, the opposite does not apply. Bigger lathes, made primarily for more experienced turners, are also usually of better quality. The biggest can still do small work, though they sometimes cumbersome. For example the toolrest holder and tailstock will be heavy to move.

But if you have limited space or budget, a good small machine will be fine for small work, and the better ones are very capable. The smallest machines, micro lathes, should only be considered if you have a particular need for one, for example if easy portability is critical. Even if you only want to make very small items, a larger machine will probably be easier to use. Drill-powered lathes are also unsuitable for general use, because of their light construction and the noise they make.

Rigidity

When choosing a lathe and comparing machines, look for:

  • a strongly constructed headstock with a large diameter headstock spindle, mounted in heavy-duty bearings that are well separated. The spindle nose thread should have a wide register at the back to support the chuck butting against it. Except on small lathes, the spindle should accept number 2 or larger morse tapers.
  • a strongly made tailstock,  that on bigger lathes can accept number 2 or larger morse tapers
  • a robust tool rest and support
  • a substantial and rigid bed
  • a strong and stable stand or bench that will support the lathe without shaking.

Look for key components made of cast iron or heavy welded steel. Cast aluminium, thin pressed steel or light weight tubular components may not be rigid enough, and heavily stressed screw threads in aluminium can wear rapidly.

Cast iron or steel bed?

It is often said that cast iron is the best material for lathe beds because it suppresses vibration, and there is some truth in this. Lathes with flimsy, light weight beds made of pressed steel are really only suitable for light work. Steel tube beds or solid steel bars can flex and vibrate, but the heavier and stronger (and shorter) they are, the better the lathe will be. Cast iron can be brittle, so is usually made quite thick and heavy out of necessity, which tends to be a good thing. A heavy cast iron bed with good cross-linking webs connecting the sides will be the foundation for a good machine.

But some top end lathes have steel beds. Heavy steel plate is welded to a heavy steel tube, round or square. The assembly is large enough to prevent twisting and flexing. Vibration on these is not a problem.

The tool rest and holder

When choosing a lathe, pay particular attention to the design of the tool rest and its holder (sometimes known as the banjo). These are key components and any weakness will prevent smooth, chatter-free cutting, particularly when using scrapers. This is specially important if the lathe has a swivel headstock as you may have to extend the holder far off the bed. The greater the overhang, the stronger the components needed to resist flexing under load. Some may bend or even break if the tool catches. Avoid rest holders with lightweight jointed swing arms. If the holder has a cam lock, it needs a heavy and rigid eccentric spindle, otherwise the clamping force will vary depending on where the holder is. Access for adjusting the tension should be easy. The hole for the toolrest stem should be deep as this will help prevent it flexing under load.

The toolrest itself should be heavy and strong in proportion to its length, with a large diameter stem. But the most heavily built rest will flex if it is too long and only has a single stem. You need a robust rest but one with a narrow top, to put the fulcrum for the tools close to the wood, minimizing tool projection. A flat top to the rest hinders proper tool movement because there are two distinct pivot points when tilting the tool.

Grip

Many turners like to use an underhand grip to anchor the tool and improve control, so the shape of the rest should allow you to grip the underside with your fingers (though some sacrifice this for the sake of greater strength, and many turners prefer the overhand grip). The rest holder and locking levers must not obstruct tool movement, when the handle is low. For this reason, it is good to have alternative positions for the stem locking lever. The side of the rest that faces you should be steep, so the tool handle can drop low enough anywhere along the rest, including directly over the stem.

The lathe should have a short and a long rest as well as the standard, as all are useful. The long one may need a second rest holder. The rest should be capable of being positioned as close as possible to the lathe axis so tool projection on thin spindles is minimised, and should be easy to move. Some seem to fight back when being adjusted.

Tool rests can be replaced if necessary.

Weight

A heavy lathe shakes less when spinning an unbalanced piece of wood. Weight comes from strong and rigid cast iron/steel construction. The stand or bench that the machine sits on must also be strong and heavy,  but it may be possible to add weights to the stand to improve stability. The lathe will be more stable if it stands on a concrete floor.

Construction quality

Machines with strong and heavy components are usually OK. But there are some points worth checking when choosing a lathe.

  • Make sure that the spindle and motor pulleys have keys fitted into slots to secure them. Some makers rely on grub screws alone, which work loose and become a constant annoyance.
  • All-over machining of the pulleys will help them run smoothly, without vibration. Check that pulleys align properly.
  • Choosing a lathe with poor quality headstock spindle bearings, power switch, electronic variable speed controller and motor can lead to trouble later. Look for components of a recognised brand, not the cheapest that the maker could find. You want them fully enclosed to keep dust and chips out, and the motor fan cooled and rated to run continuously. Cheap motors run hot.
  • See that the top surface of the bed is smooth and true. A bed with a flat top may be easier if you want to fit accessories such as a steady rest. Be sure that the headstock and tail stock can line up accurately with each other. Any apparent error could be due to an uneven floor causing the bed to twist slightly, and easily corrected.
  • Make sure there is no detectable play in the tailstock ram when extended and locked. Also that the tailstock slides freely but locks immovably to the bed. The revolving tail centre must have no play in its bearings when under load (this is a replaceable item).
  • Make sure that the headstock spindle has no play or end float – fit the faceplate and see if it will move.
  • Make sure also that the tool rest holder and the tool rest itself move freely and lock immovably at all positions. Some will lock when close to the lathe axis but not when further out.
  • The screw threads that lock the toolrest and tailstock ram should be generous in size and snug-fitting. The points of the locking screws should not cut into the metal. The handles should be strong and preferably of steel, not plastic.
  • Poor paintwork and sharp edges on the castings suggest a lack of attention to detail at the factory.

Choosing a lathe for ease of use

It’s important to consider ergonomics when choosing a lathe. Good ones are designed for ease of use, and fit your particular needs. Look for spanner-free adjustments. See that the locking levers don’t get in the way (particularly the one that locks the toolrest stem – try it with the holder in different positions). Make sure that they are robust. Plastic levers will break in time. Levers adjustable for angle are useful. It should be easy to remove the tool rest holder from the lathe. Ideally this should be possible without removing the tailstock or dismantling anything.

If you are choosing a lathe primarily for making bowls and boxes, you may find it much better to be able to work from the front of the piece without having to bend over the lathe bed. A shortbed lathe, or one with a swivel or sliding headstock or with outboard turning provision lets you do this (though short bed lathes obviously sacrifice capacity, and you never know what lengths you may want to turn in future). But other turners are happy to work over the bed and don’t mind bending. A swivel or sliding headstock also prevents obstruction of the tools when the handles hit the lathe bed.

There should be an indexing arrangement for a swivel headstock so you can quickly return it to parallel. It is possible for debris to get under a swiveling or sliding headstock, affecting its rigidity and alignment. The tailstock could also be affected. I have not found this a problem in the lathes I have owned, but good design would minimise the risk. In particular, the headstock should not tilt when you loosen it. As long as it sits flat on the bed it will be difficult for chips to get between the metal surfaces.

When turning spindles, you will need to get close to the work. Make sure there is no obstruction to your feet that will force you to bend forward. If on a bench stand, the lathe should be well to the front, as consistent with stability. A gap underneath for your toes is good, though it will accumulate shavings.

The height of the lathe spindle is important if you use it for hours at a time. The usual rule is to have the axis at, or a little above elbow height. Then you don’t have to bend. But it depends on the individual. You may have to experiment to find the most comfortable height for you. Some lathe stands are adjustable for height. But it is normally possible to raise the lathe on blocks or to stand on a platform when working.

The headstock spindle and tailstock ram are best hollow. This allows you to use a knock out bar, and you can drill long holes on the lathe.  It’s nice if the tailstock taper is self-ejecting. An easy and effective spindle lock for the headstock is important so you can remove chucks. Provision for dividing is useful for some work. But the division holes should not double as the spindle lock, unless they and the locking pin are substantial. Otherwise the holes will soon wear.

A headstock handwheel that lets you turn the spindle is useful when inspecting  the work or winding on chucks. The tailstock handwheel should be generous in size and operate freely. A place to keep calipers, sandpaper etc is useful. There is often a flat top on the headstock for this. You also need somewhere to fix adjustable lights. But these aren’t necessarily on the lathe.

Unless you know you will not need to turn pieces bigger than the capacity over the bed, when choosing a lathe go for one with provision for outboard turning. Or one with a sliding or swivel headstock. You can use a freestanding tool rest, but they are often unsatisfactory. Unless they are rigidly locked to the lathe, they can tilt or bend inwards, causing a catch. Sliding headstocks and outboard toolrests may need more space in use. You need access to the ends of the bed and you may have to remove the tailstock. The tailstock cannot be used with a sliding headstock when it is moved right to the end of the bed. Nor when the headstock swivels.

Motor power

Choosing a lathe with insufficient power will slow you down. A 1/3 horsepower motor is about the minimum for a small lathe. It will do for small spindle work and for small bowls when cuts are light and work done slowly. Under-powered lathes stall easily, which is annoying. One horsepower will do for medium size bowls. It is enough for large ones if you use the low-speed pulley setting and take light cuts. Two to three horsepower will let you work at a natural pace on large pieces without stalling the motor. Large motors may need permanent wiring rather than just a domestic style plug and socket. Large motors are less safe for a beginner, because they can apply a lot of force to the tools.

Noise

The lathe itself should run quietly, though when cutting there will be more noise. You will soon tire of rattles and bearing noise. The lathe should have an induction motor, not one with brushes and gears. The drive belt should not be tensioned solely by the weight of the motor. This can cause it to bounce, which can lead to noise and vibration. To avoid this, there should be a lock for the motor. The motor should, ideally, be directly below the spindle to minimise shaking.

Speeds

When choosing a lathe, look for one with a good range of lathe speeds. Low speeds, preferably down to 200 rpm or less, are more important than high. This is because it is unsafe to spin unbalanced chunks of wood fast even on a heavy machine. If the wood is sound, balanced, secure and not too large, turning at higher speeds is usually best. But you will get used to whatever maximum speed your lathe has. Many lathes these days have electronic variable speed, and this is a great feature. Even more so if it goes down to zero and can reverse the lathe. The very low rpm you can get from a good variable speed unit can be useful. It helps if you want to apply finishes to work while it is still on the lathe or to sand green-turned bowls.

But step pulleys work well, provided that it is easy to adjust the speed. It should not be necessary to go behind or underneath the machine, unlock covers or use spanners. Even with good quality electronic variable speed, it is very useful to have step pulleys. This is because their lower speed settings give more torque. You can often upgrade a lathe to electronic variable speed, but at significant cost. Some lathes have mechanically variable speed, with lever-operated cone pulleys. I have little experience of these, but they are said to be unreliable unless well made and to cause rapid wear on the belt. The unit on the lathe at my turning club has not held up well. Adjustment is only possible when the lathe is running.

Accessories

Make sure the lathe is ready to accept headstock and tailstock accessories. Choosing a lathe with a non-standard spindle nose thread will make it hard to find chucks. Avoid machines that do not allow use of Morse taper fittings in both headstock and tailstock.

 

Posted on

Homemade long tool rest

A homemade long tool rest can be a useful accessory. It’s a great help if the tool rest is longer than the spindle you are turning by at least 25 mm at each end. This gives tool access to the ends of the spindle, and it’s much easier to turn sweeping curves accurately if you don’t have to keep moving a short tool rest. Few lathes come with a very long tool rest as standard. They can often be bought as an accessory, at substantial cost. Over a certain length, they need two stems to keep them rigid and stop chatter.

It’s quite easy to put together a homemade long tool rest and a second holder for it using hardwood. A wooden tool rest is pleasant to use, and was standard in past times. You will need to remove the sharp side edges on skew chisels to protect the wood. But that’s necessary for steel rests too. You may have to plane or sand the top smooth from time to time.

The stems

Make the two stems of round steel bar. One needs to fit your existing tool rest holder. The other can be any size because you will drill the holder to fit. The length should bring the top of the rest to the proper height when it is fitted into the wooden holder.

Drill a hole in one end of each bar, using a tapping drill that matches some threaded rod. Tap the thread and screw in a short bit of the rod. Tighten it in the hole so it stays secure. If you insert the rod about 25 mm deep and it projects about the same distance that will be about right. If you don’t have a tap, you could drill a larger hole and use adhesive to keep the threaded rod in place.

The rest

My homemade long tool rest began life as a table leg, about 600 mm long, 40 mm thick and 50 mm deep. I find it quite strong enough. Plane the front to make a slope. Drill two tapping size blind holes in the wood for the threaded rod, about a quarter of the way along from each end. Screw in the stems.

You could tap the holes, but most hardwoods will not make a good thread using an engineer’s tap. If you cut the end of the threaded rod cleanly, the rod should make its own thread in the wood. This is the method I used. You could drill the holes larger and use epoxy instead, or glue the stems into the wood without using threaded rod at all. The main thing is to make sure the stems are parallel to each other and securely held in the wood.

The holder

Use hardwood, say 60 mm thick, and drill a blind hole, say 45 mm deep, at one end for the second stem. Wood will probably not be strong enough to take a locking screw that will hold the stem firmly, so that limits height adjustment. You can raise the rest a little by putting a spacer in the hole under the stem.

Saw a slot in the holder that will fit over a clamping screw to hold it on the lathe bed.

A steel version of this holder could have a locking screw to allow height adjustment.

The clamp

Now make a clamping block that will fit your lathe bed. Its design will vary because all lathes are different. Mine is made of thick MDF and fits between the ways. It has a projecting lip underneath. A bolt passes through the block and is long enough to reach up through the wooden holder, a washer and a nut that will clamp the holder in place on the bed.

homemade wooden tool rest
My long tool rest, with a block of redwood waiting to be turned.

 

tool rest holder plan view
tool rest holder plan view
cross section view

 

Posted on

Harden steel using these simple methods

It’s sometimes useful to know how to harden steel. Although it’s possible to do woodturning with very few tools, I can never resist trying something new. Sometimes I buy tools, but often I make them myself. Back in the days before commercial tools were available, turners knew how to harden steel and temper it. They made their own tools out of high carbon steel, or got them from the local blacksmith. The best way to harden steel and temper it is to do it properly by modern methods. This requires the right steel for the job, with careful control of temperatures and timing and the rates of heating and cooling. But acceptable results can usually be obtained using the cruder methods described here.

Tool steel

Turning tools are now rarely manufactured from carbon steel, but it is still used for many other purposes. Even for turning tools, it still works as well as it did when the old-time turners made their living with it. You can buy high carbon steel in various grades from steel stockholders, some suitable for hardening in water and others in oil.

Scrap carbon steel is easy to find. If you want to harden steel for tool making, springs, files, saw blades, masonry nails, crow bars, cold chisels, woodworking chisels, old screwdrivers, plane irons and many other things are steel that is suitable for reworking. I have used the tines of an old garden fork and the rings from old ball races. Keep in mind that if you put the tool under significant stress, steel that has or may develop cracks is unsuitable. For example, the valleys between the teeth of a file are weak points where cracks can start.

If you are using scrap, old steel is often the best choice because some modern steel alloys may not respond well to these basic heat treatment procedures. One way to tell what you’ve got is to touch the steel on a grinder. Lots of bright bursting sparks like a child’s ‘sparkler’ firework mean it is probably high carbon steel. Try a bit of mild steel such as an ordinary nail for comparison. It will also make a lot of sparks, but there will be fewer bursters. The use of the metal before it became scrap is a clue – if it was subject to a lot of stress, the metal is probably high carbon steel. But there is a continuum of carbon content – to be sure, test-harden a piece before making the tool.

Low carbon mild steel

Ordinary low-carbon mild steel is not suitable for most cutting tools. You cannot harden steel of that kind, and it will not keep a sharp edge. To harden steel, the metal must have a high enough carbon content. The metal is harder than wood, and a cutting edge on mild steel may last long enough for a one-off job. But if the edge is thin it will just give way under pressure. You can case-harden mild steel. This gives it a very thin layer of higher carbon content on its surface. Then you can use it for some light-duty cutting tools provided you don’t grind away the hardened skin when sharpening. To case-harden, coat the metal with a special compound before heating. You can use mild steel as a holder for inserted or brazed-on cutters.

Equipment needed

To harden steel, you must first make it hot. You can use a magnet to check that it is hot enough for hardening – when the magnet stops attracting it, the steel is ready. More simply, just get it red hot, which is also the temperature needed for hot forging. The bigger the piece, the more heat you will need. If the item is small, you can harden steel using a burner on a gas cooker. You can use a charcoal fire with a blower to supply air.  You can do a lot with a reasonably powerful blowtorch. Larger pieces of steel may dissipate the heat as fast as it is applied, never getting hot enough. If using a blowtorch, you can stack a few dry bricks to make an enclosure to retain the heat.

A simple forge burning solid fuel or propane is not hard to improviseThere is video on YouTube about making a simple but very effective propane forgeI made a forge that burned anthracite and worked 7/8 inch bar without too much trouble. More recently I made a propane forge using just two insulating fire bricks and a blowtorch, and was able to bend steel strip of about 2 inches width and 3/8 inches thick.

Hot forging

If you make two pieces of steel white hot, you can weld them together by hammering. Hotter still, the metal will burn and spoil. But these temperatures are harder to reach with the sort of equipment described.

If you want to do any hot forging, you will need something to use as an anvil, a hammer, vise and heavy pliers. You may also need a hacksaw, angle grinder, file, bench grinder and a drill press. To work thick steel, you will need heavier tools and a forge.  If it’s hot enough, it’s surprisingly easy to bend steel using a vise or wrenches, or to hammer it into shape on an anvil. You can forge ordinary mild steel in the same way.

Annealing

Some scrap carbon steel is too hard for sawing or filing into shape. You will have to anneal it to make it softer and workable. To do this, the first step is to make the metal red hot. While it is hot, you can forge it. Don’t try to work the metal when it has lost its red heat or it may crack. You have to strike while the iron is hot. After any forging, get the steel red hot again and then anneal it by cooling it slowly. The slower it cools, the better – traditionally the metal was left to cool buried in hot ashes. If using a propane forge, you can just leave the metal to cool in the forge so the residual heat will slow the cooling. You want the whole piece uniformly softened, so try to heat and cool it evenly.

When cooled, the annealed steel should be soft enough to file. Check that all parts are soft, then carry out whatever further operations you need. Shape the tool, including rough grinding the edge.

Harden the steel

To harden steel, heat the part to be hardened bright red hot again, if possible ‘soak’ it in the heat for a bit, then quench it. It’s the rapid change from red hot to cold that will harden steel. You can use various quenching liquids, but a bucket of water will usually do the trick. Plunge the red hot metal straight in, and swirl it about to cool it as rapidly as possible. If the steel warps or cracks when quenched, try using oil instead of water, or use different steel. If using oil, fire precautions are necessary. Use a metal container, not a plastic bucket. The hot steel will heat and ignite the oil, so have a metal cover handy to extinguish the flames.

You don’t always have to harden all parts of a tool to the same degree. If it must withstand stress in use, you can leave the bulk of it soft, for toughness and strength, with just the cutting tip hardened.

After quenching, the steel should be glass-hard and a file will just slide off it without cutting. Don’t try too hard with the file, the hard metal will soon make it blunt.

Tempering

The freshly hardened tool will be brittle. If you were to use it in this state, the edge could chip or it could shatter. For most purposes, you must heat it one more time to temper it before use. Tempering takes away the brittleness. It makes the metal tougher, but softer. The higher the temperature reached during tempering, the softer and less brittle the steel will become. Each tool has its own optimum compromise between hardness and toughness.

Before tempering, clean up the metal using abrasives. You want the steel bright and shiny for this stage. Warm the tool very carefully above, not in, a clean flame. Watch the bright metal surface carefully as it heats up. Let the heat start away from the edge and creep towards it, aiming for a uniform temperature over the surface. The edge and any other thin parts will heat up too fast if exposed to the heat directly.

Watch the colour change

As it gets hotter, you will see the bright steel change colour. It will go from silvery to a pale yellow, through brown to blue and then to grey. You have to catch the moment when the colour you want reaches the edge. Normally a pale yellow-brown colour at the edge of a cutting tool is about right for cutting wood, but different tools may need other colours. A blue colour will leave the steel tough and strong, but not hard enough to keep a cutting edge. (Springs are tempered to blue, and some steel components such as screws are blued for decorative purposes.)

Don’t let it get too hot

If you let the metal get too hot you will have to repeat the hardening stage. You can repeat the annealing, hardening and tempering without harm to the metal. But too long at high temperature can tend to burn out the carbon from the surface layers. When the colour is right, quench the tool again. It is then ready for final clean up and sharpening before being put to use.

Sometimes you need more accurate tempering, for example if you need a larger piece evenly tempered. You can do this by heating the item in an oven at a set temperature, or in oil. You will need a thermometer for these methods. They allow for soaking at the proper temperature, which may give better results.

 

Posted on

Hazards in a woodturning workshop

There are some significant hazards in a woodturning workshop. Some of them are specific to turning and some are common to all woodworking. The hazards that can cause ill health and injuries in industrial workplaces are just as much an issue for hobby turners. Perhaps more so, as the law provides some protection for people at work, including in the UK a requirement for adequate information, supervision and training to be provided to employees. Amateurs working alone may only discover the dangers the hard way, which is a good reason to go on a turning course.

But you can take precautions, and most turners survive with nothing more than minor scratches from time to time. The risks are manageable if recognised. An absorbing occupation that helps keep you active has health benefits too. Turning is fun, and perhaps no more dangerous than other kinds of woodworking. And which activity is free of any hazards?

Some of the risks can be minimised by well-known safety rules such as keeping guards on machines and wearing face protection. Often, people ignore these rules and just work carefully. It’s their choice. But it’s hard to be careful all the time, and probably most people who get hurt thought they would be OK as long as they were careful. But there are some hazards that can’t be eliminated, so only being careful will protect you against them – for example you have to avoid getting your fingers caught between the spinning wood and the tool rest on the lathe. Care, alertness and good working habits are always going to be necessary, and they become second nature.

Dust

All turners know that dust is one of the hazards, but often aren’t sure how dangerous it is. Turners are exposed to dust concentrations significantly higher than the safety standards set for industrial workers. But few are exposed for eight hours a day, every day, the assumption behind those standards. Only a small proportion of hobby turners are likely to suffer serious harm.

Dust control is achieved in the turning workshop by effective collection at source, with a breathing mask if the extraction fails to capture all the dust. For more information, see my articles on wood dust and dust control.

Machinery and turning

Spinning wood can badly injure or even kill people. If spinning too fast, it can break up. The fragments will then fly in a straight line with all the kinetic energy given to them by the lathe motor. A key left in the chuck when the lathe is switched on will be flung out. An incorrectly presented tool can dig in, wrenching the wood as well as perhaps throwing the tool. If the timber is not held securely, it can come loose and hit someone, but while it remains in one piece, much of its kinetic energy is rotational. You don’t want it hitting you, but if it does, the force of impact will usually be less than the hammer blow you could receive from half of a large bowl blank.

Sharp edges on the rotating timber can cut. The rotating drive centre or chuck, and the workpiece, can entangle hair or clothing, pulling you in with great and sudden force. Something will have to give, and that’s a battle the lathe will win. Rags or steel wool wrapped round your fingers can drag them in. Projecting chuck jaws can trap your fingers against the tool rest or send a sharp cutting tool flying. The hollow Morse taper in the headstock will grab anything put into it, including a finger. The lathe’s drive belt could easily break your fingers against the pulley. A poorly presented cutting tool catching in the wood and snapping down onto the toolrest can pinch fingers. A Jacobs chuck can work loose from the spindle taper and perhaps be flung across the shop.

Turners typically use other machinery, including bandsaw, chain saw, grinder, sander, drill, table saw and others, all with their own specific hazards. They may have rotating cutters and parts that can entangle hair or clothing, finger trapping points (for example between a grinding wheel and its tool rest).

Tie back long hair when using any machinery with exposed rotating parts. Don’t wear long sleeves or loose clothing or jewellery that might catch. Don’t take chances with poorly gripping chucks or weak fixing on a faceplate. Keep the lathe speed down when turning heavy pieces, particularly when they are not balanced – always check the speed before switching on. Don’t use timber with dangerous cracks or bark inclusions or rotted areas. Keep out of the ‘line of fire’. Make sure the off switch is within reach. Take off the sharp edge on a bowl rim with a tool or abrasive. Don’t use a chuck with projecting jaws. Don’t ever put your finger into the taper while the lathe is running. Move the toolrest out of the way when sanding. Use paper instead of rag when polishing, and don’t wrap steel wool round your finger.

Never leave the chuck key in the chuck. Handle cutting tools with care around the spinning wood to avoid accidental contact, and don’t have your finger between the tool and the toolrest. Don’t turn large heavy pieces until you have plenty of experience of smaller ones – learn to walk before you run. Some lathes have steel mesh guards to stop flying chunks of wood. Wear good quality full face protection, properly adjusted – chips can fly up under a face shield and get in your eyes, unpleasant at the least. Don’t use gloves if they might catch. (If flying chips hurt your hands, reduce the speed or put a chip deflector on the gouge. If your hands are cold, turn the heating up.) And if using a Jacobs chuck without tailstock support, fit a draw bar to keep it secure.

Make sure you understand the machines, their hazards, and good practice in their use (for example the danger of kickback on a table saw is not immediately obvious to a beginner). Don’t use the machines beyond their safe limits. Keep guards in place when the machines are in use, and use appropriate personal protective equipment. Full face protection is advisable at the lathe – safety glasses are not sufficient.

Bandsawing timber for woodturning has some particular hazards. For example, cross-cutting round timber can cause the blade to grab and bind. This can jerk your hands into the blade or crush your fingers between the wood and the saw table. It is best to hold the timber with a clamp to stop it rolling into the blade. Any blank without support under the point of the cut can tilt into the blade. Sawing spalted wood can sometimes be a problem. You may be pushing the wood into the saw when the blade enters a soft patch and the wood suddenly shoots forward. You should never push with your hand in line with the blade. When cutting discs, you may also find the wood shoots forward suddenly when the blade comes out of cut after sawing off the corner of the blank.

Electricity

Fatal electrocutions are rare, causing only a small percentage of industrial deaths. But electric shocks that fail to kill are much more common. Whether a shock is fatal often comes down to luck – it depends on whether there is a low resistance path for the current to earth at the moment when you are shocked. If, for example, you are standing on a wet concrete floor or have your hand on a machine that is earthed, more current will pass through your body, and it may kill you.

Ensure that all wiring and appliances are in sound condition. Check flexes and plugs from time to time. Use an earth leakage device that will disconnect the power in the event of a shock. Don’t use unsuitable electrical equipment in damp conditions. Don’t use makeshift, substandard wiring or ‘temporary’ unsafe fittings.

Falls

Slips and trips are the commonest causes of injury in the workplace.

Keep the floor clear of hazards and anything slippery, and keep the working area well lit. Don’t climb on makeshift steps or unstable platforms from which you could fall. Repair any holes in the floor. Don’t let cables and hoses trail across the floor. Clear up off-cuts. A floor can become slippery as the surface wears, or if oil finish, wax polish (or wax sealer from turning  blanks, a particular problem) or sawdust gets on it, so may need attention. Don’t forget the route to the workshop. If you have to go down an unlit garden path with icy patches and steps, it’s only a matter of time before gravity gets you.

Heavy objects

Chucks and bowl blanks, and sharp tools can easily cause serious foot injuries if dropped. Keep working areas tidy so that chucks etc. are less likely to fall or be dropped. Have a good place to keep tools when they are waiting for use – don’t just perch the skew chisel on the vibrating lathe bed. Wear shoes with steel toecaps.

Manual handling

Back strains caused by lifting are extremely common. Moving logs or machinery can injure you. The risk does not just depend on the weight of the object; other factors come into play, for example, if workshop clutter forces you to move awkwardly when you pick up a large bowl blank. Use a trolley to avoid unnecessary lifting. Break the load down if possible. If you have to do some lifting, plan it. Clear the working area so you don’t trip. Get help.

Fire

There are several ways in which a fire can start in the workshop. Steel wool very easily ignites from sparks. Oily rags can catch fire spontaneously. Shavings caught up above the bulb of a work lamp can get hot enough to start smouldering, allowing embers to fall into shavings beneath. Cigarettes can fall into shavings. Fire is always dangerous and could destroy the shop, perhaps after you have locked up for the day.

Don’t leave steel wool near sparks from the grinder, or in a drawer with batteries (contact with their terminals will ignite it). Spread out oily rags to dry before disposal. Use lamps with open shades that won’t trap shavings. Keep an extinguisher where you can find it straight away. You know what you should do about smoking – it’s a lot more dangerous than woodturning.

Oh, and don’t superglue yourself to the lathe when there is no-one about to rescue you!

Posted on

Wood dust and the hierarchy of control measures

People sometimes misunderstand the facts about wood dust. If you are a woodturner, this is what you should know.

All dust is a hazard

All airborne wood dust is hazardous. That includes hardwood dust, softwood dust and MDF dust. MDF dust is not worse than other kinds. But it easily makes a lot of dust, and more dust can mean more risk. All are capable of causing serious harm such as dermatitis, breathing problems and even cancer. It is not a question of the wood’s toxicity or your individual sensitivity. If some timber species are more dangerous than others, it is hard to say which ones. The proof of harm comes from the mortality of long-term workers in the furniture industry, working with timbers such as beech.
A ‘hazard’ is something with potential to cause harm. That doesn’t necessarily mean that harm will result. That depends on the degree of exposure to it, what precautions you take, and possibly individual susceptibility. The likelihood that harm will actually result is the ‘risk’. As a woodworker, you expose yourself to the dust hazard. To protect yourself, you have to control the risk to the extent you are comfortable with.

Risk depends on exposure

The risk depends on how much dust is present and how long you spend breathing it in. So an occasional turner working green (less dusty) wood is at less risk than the dedicated person who spends long hours hunched over the lathe hand-sanding dry and dusty stuff. Only a small proportion of those exposed to wood dust are likely to get cancer as a result, but turners can easily expose themselves to very high dust levels, well above the legal limit for commercial workshops, at least for short periods. There is no absolutely safe dust level, but if you keep within the legal standards for commercial workplaces the risk is low.
There may be species of wood that you as an individual are allergic to. You may develop dermatitis or breathing problems even after minimal exposure to them. But other species to which you are not now sensitive are hazardous to you as well, just as they are to other people. And you may develop an allergy to another species at any time, even after years of working with it.
Lots of things in the turner’s workshop generate wood dust. Turning, sanding, sawing and sweeping all make clouds of dust. Special lighting reveals it. The fine particles that are most hazardous are almost invisible in the air, and stay airborne for a long time.

Commercial workshops

In a commercial workshop in the UK, the COSHH regulations apply. They require that the risk of wood dust is kept at a level that is unlikely to result in harm. This should preferably be done by using work methods that do not generate dust. Failing that, by removing the dust at source before anyone breaths it in, or by using personal protective equipment such as overalls and breathing masks. In commercial workshops where the law applies, that is the order of choice required. This is a sensible rule in other places too, because masks are never fully effective. It is much better to keep the dust out of the air in the first place.
Posted on

Dust control at the lathe. What works best?

Dust control is an important issue for woodturners. We work in an environment where hazardous levels of dust are in the air we breathe. Turning generates dust, and breathing dust is harmful to our health. It can cause breathing problems or cancer. Dust on the skin can lead to dermatitis. All types of wood dust are hazardous, including softwood dust, though some are more likely than others to cause allergy.

The best dust control is not to make dust. Keeping tools sharp, using the less dusty timber species, and wet sanding with water, oil or wax instead of dry sanding, will help reduce dust levels. But most turners make dust and need a way to protect themselves. There are several options for dust control.

Breathing mask

This is the easiest, and at its most basic, the least expensive dust control option. A mask can be effective for low levels of exposure. It may be appropriate for people who do not turn often or for long periods of time, where the cost of dust extraction is not justified. But it is not the best primary protection for most turners. There are several reasons for this.

A mask must seal to the face to prevent unfiltered air flowing under the edge, so a beard is a problem. The filter may impede air flow. The mask may be uncomfortable to wear. Some may cause spectacles to fog. If it doesn’t seal properly, or you take it off when the job is done, you will breathe dusty air. Hazardous dust is so fine that it remains suspended in the air for a long time after work stops. Although a well-fitting mask can protect the wearer, it can only do so while it is being worn.

For many, the best kind of mask is a powered unit that filters the air before blowing it over your face. These can be comfortable, or at least acceptable for hours of use, as the positive fan pressure means that the mask doesn’t have to seal to your face. In addition, the visor and helmet may be impact resistant. If you wear spectacles the air flow will help stop them fogging. But you will still breathe dust when you take the unit off, and a mask will not prevent dust from contacting your skin.

Air cleaners

These filter the workshop air to remove background dust. But they aren’t a complete answer. Most importantly, you work closer to the dust source than the air cleaner does, so the air you breathe carries the heaviest load of dust. A cleaner takes a significant time to remove all the suspended dust in the shop. It’s not just a matter of comparing its rated airflow with the volume of the workspace. The filtered air mixes with the unfiltered, diluting the dust concentration, which goes down slowly as the air passes through the cleaner multiple times. You should put the air cleaner where it will set up a circulation of filtered air around the shop, but there are always likely to be dead spots where dust removal is slower.

Air cleaners are a supplement to dust extraction at source, not primary protection.

Fans

Some people suggest a fan to blow the dust away from the turner. In the right conditions this could work. It will cut the concentration in the inhaled air even if the dust remains in the workshop. If there is enough general ventilation in the shop, the concentration may not build up to harmful levels. But it is not normally a reliable method. The ventilation and the direction of airflow from the fan may vary, and dust may reach harmful levels without you knowing.

Dust extractors

A dust extractor catches the dust at source, before it gets into the general air circulation of the workshop. This is in principle the best solution. It’s the reason workplace health legislation prioritises extraction over the other options.

But not all extractors are suitable. The lathe is a difficult machine to extract dust from. The dust source may be anywhere along the lathe bed or across a spinning disc. The work throws the dust in all directions, including towards you and away from the extraction inlet. Meanwhile, you are bending over the work and breathing in the highest concentration of dust.

The suction has to overcome the speed of the air movement generated by the spinning work. Dust from the tool or from sanding will go with this moving air, which may be quite rapid. You can feel the wind coming off the edge of a spinning disc. This means that a powerful extractor is necessary.

Unfortunately, the suction from any extractor falls off very rapidly with distance from the inlet. At a distance equal to the diameter of the inlet, the air speed is only about 10% of what it is in the mouth of the inlet. This is because the air enters the inlet from all directions, including from behind it. Therefore, to capture the dust effectively the inlet diameter needs to be large, so the dust source can be within its effective zone; it must be adjustable so it can be positioned close to the dust source;  and the extractor must be powerful enough to provide sufficient airflow through the large inlet. Although any extractor is better than none, it’s not enough just to use a large collecting hood if the extractor is too small for it.

It is important that the extractor has a fine filter, or exhausts outdoors. If it doesn’t, much of the dust will return to the workshop. Although a layer of dust inside the filter will itself act as a fine filter, it will also reduce the airflow. With a fine filter, an extractor left running will act as an air cleaner.

Types of extractor

There are two kinds of extractor – high volume, low vacuum; and low volume, high vacuum, which are similar to domestic vacuum cleaners. Lathe dust control needs a high volume air flow to capture the dust, and not high vacuum. There is an overlap between these types of machine, and some powerful high vacuum machines are able to move more air than a small and inefficient low vacuum one.

It is important to check the cubic feet per minute specification. Don’t mistake the high suction that you feel when you put your hand over the inlet for high airflow. The vacuum will pull hard when you block the inlet. But comparatively little air is moving through the pipe when it is open. The amount of airflow needed depends on the turning being done – larger diameter items and higher lathe speeds need more airflow. As a general principle, more is better.

High vacuum machines are very good when the pipe connects directly to the source. But at the lathe, the inlet must move as the source moves, which is not always practicable.

Other dust control issues to take into account are noise levels, ease of emptying, and the quality of the ducting. Ductwork should be as short and straight as possible, as bends and even straight sections increase friction and reduce airflow. Smooth bore ducting causes less friction than corrugated flexible pipe. Leaks at the joints and at blast gates reduce airflow at the inlet. The ducting should be large diameter to reduce friction, but not so large that air moves slowly through it and deposits chips.

Whatever kind of extractor is used, it will often fail to get all the dust. A dust mask can then be used to supplement the extractor.

Posted on

Sharpening gouges with a jig

Setting Varigrind cup position

Sharp tools are critical to good work, as all turners know. If the tool is blunt, the wood rejects the cutting edge. If you force it to cut, it tears the grain. But sharpening bowl gouges and spindle gouges can be a challenge. It is perfectly possible to sharpen them freehand, with or  without the help of a platform set at the correct angle, but these are skills that take time to learn. Most people prefer sharpening gouges with a jig. I use a Oneway Varigrind jig, the type to which this article refers.

 There are others on the market, some designed to work with a grinding wheel, which I prefer, and others with a belt sander. There are plans online for making them. They all work in a similar way – they hold the tool to the grinder at a set angle while you shape the edge. They make sure the bevel angle is consistent, but even sharpening gouges with a jig doesn’t guarantee the shape of the cutting edge. You control that yourself, by grinding a bit more here or a bit less there.

 Once set up, jigs are quick and easy to use, and can give a consistent and accurate grind, removing the minimum of metal and producing a clean bevel. But how do you set them up?

 The key is to use setting templates. Up to three are needed for each grind, but they can be made very easily. None of the jig settings are critical, as slight variations will make little difference to the sharpened gouge. But the more consistently the jig is set, the less grinding will be needed, so the tools will last longer.

 Duplicating an existing grind

 If you have a properly ground gouge to start with, you can make templates to reproduce that grind. It will then be easy to re-set the jig at any time, so you can either sharpen the original gouge, or duplicate its grind on another one.

The first step is to set the jig to match the gouge. Use a marker pen to blacken the bevel on the gouge (this is only needed when setting up the first time). Put the gouge in the jig with the correct length projecting, following the jig manufacturer’s recommendation. Two inches is about right. Set the angle of the jig to about the middle of its range, and put the jig in place in the pivot cradle on the extending arm, tilted over as if to grind the wing of the gouge. Extend the arm until the wheel best contacts the wing bevel. This can be seen from the bright streak where the ink is removed when you turn the wheel by hand. It won’t contact fully unless the wheel is the same size as that originally used.

Put the jig in its central position and change the jig angle until the bevel at the nose of the gouge is in contact with the wheel. Now go back to the tilted position, and adjust the arm again as necessary.

A couple of repetitions to set the wing, then the nose, then the wing and finally the nose again, will home in on the correct jig angle and arm position for that gouge. Remove the gouge from the jig, and make templates (see below) to fit the jig angle and the arm position that you have established. Label them.

 Changing the grind

 If you want to change the grind of a gouge, you have to keep adjusting the jig and grinding the gouge until the required angles and shape are achieved. Then make the setting templates. If you know the angles you want, a machinist’s protractor will help get the settings right. The variables on the gouge are the bevel sharpening angle; the sweep angle of the wings (the angle at which they are ground back from the nose); and the profile of the cutting edge. A fingernail profile with a 40 degree sweep and 40 degree nose bevel angle would be good for a bowl gouge, but other angles are useful too.

Reshaping

If you are extensively reshaping a gouge, rough out the new grind on an angled platform before starting with the jig. For example, if you want to make a ‘40-40’ grind, start by grinding the 40 degree nose bevel square across without rolling the gouge. Then turn the gouge flute-down on the platform and grind the 40 degree sweep of the wings. The curve of the wheel rim will make the top of the wings concave, so lift the handle slightly when grinding the nose and push forward slightly when grinding the wing ends to make their tops flat. In this somewhat brutal process, the old cutting edge will be ground completely away, but you will clearly see the shape of the finished grind.

 The bevel angle to be ground on the wings is hard to judge without an example to copy. (Perhaps someone can suggest a method?) It’s less than that on the nose, because the inner sides of the flute are angled upwards, and it differs at each point along the wing. The included angle should not be too acute as that will make the edge weak and grabby in use. With no example to guide you, put the gouge on the 40 degree platform. Swing it to the side and roll it until the side of the flute is parallel to the platform. Then grind a bevel. You will then have a part ground gouge with a correct nose angle. It will have a provisional side bevel that you can use to set the jig as above.

 Sharpening gouges with a jig

When sharpening gouges with a jig, or completing a new grind, set the tool in the jig using the templates. Grind the wing on one side, then the other, taking care to keep their tops flat and at the required sweep angle. Don’t let the weight of a long gouge and handle push the jig forward in the cradle. Tools with detachable handles are easier to grind. Roll the jig from just off centre over to one side, without pressure, letting the weight of the gouge do the work. Do the other side, then lightly grind the nose, blending it into the wings to form a smooth curve. Too much pressure, or dwelling too long in one spot, will quickly spoil the shape.

Check the shape

Take care  not to make the nose pointed or square-tipped. Keep it level with the wings, not peaked or dropped. If reshaping the gouge, the flat tops will guide you. But before completing the grind, assess the wing bevel angle. Adjust the jig if necessary.

The wings should be straight in profile, or slightly convex, not concave. It can help, particularly when grinding the nose, to switch off the grinder and use its momentum to work as it slows down. This makes the grinder less aggressive. A perfect grind is rarely essential, so if there are minor errors, it’s usually possible to do some turning with the gouge before correcting them during the next sharpening. After a bit of practice the sharpening becomes quick and easy.

 Making the templates

 The first is a template to set the jig locking angle. Its design will depend on the grinding jig. Identify two reference points on the jig and make a template to position those points. For the Varigrind, I use two scraps of ply glued together in a wide, flat V. One arm rests against the face from which the gouge protrudes. The other rests against the side of the pivot arm).

Template to set Varigrind jig angle
Template to set Varigrind jig angle

 

 The second is a template to set the gouge projection. At its simplest this can be a stop block the right distance from the edge of the bench. I drilled a blind hole of the right depth in a scrap of wood and fixed it to the bench. A coin in the bottom of the hole stops the gouge nose digging in. I stand the jig on top, face down, and insert the gouge so it is standing free in the hole, then tighten the jig clamp. It is not normally necessary to change the projection.

 The third is a template to set the distance of the jig cradle from the wheel. It’s best to reference from the wheel itself, to allow for wear. A simple dowel of the right length would work, but would not be as positive as a spacer with two-point contact. I use a narrow triangular scrap of board. I curved its shortest side to fit the wheel rim. It has clearance in the middle so it contacts at two points. The triangle is long enough that the opposite point reaches the cradle.

Setting Varigrind cup position
Template to set Varigrind cradle position