Posted on by — Leave a comment

Homemade compasses, any size you like

Here is a useful tool for turners – a giant pair of homemade compasses. When preparing large bowl blanks the usual commercial compasses may be too small. I made a large pair from scrap wood. Opened to 90 degrees, they can make a circle of 800 mm radius. You could make them any size you like.
My pair has arms about 550 mm long, made of planed scrap softwood. They are joined at the top by a small coach bolt, washer and wingnut. One arm has a pointed nail inserted, the other has a simple clamp to hold a pencil. Drill the hole for the coach bolt the same diameter as the bolt. The square part of the shank will pull into the hole when you tighten the wingnut, and stop the bolt turning.

The point

To insert the nail, drill a small hole in the end of the arm. The hole should be just a little less in diameter than the nail, to make it secure without splitting the wood. Cut off the head of the nail and grip it point down in a vise, then tap the arm down onto the blunt end. Cut the arm to a blunt point so the corners don’t get in the way.

The pencil clamp

To make the pencil clamp, drill a hole for the pencil first, making it a sliding fit. I shaped the end of the pencil arm a bit, but that isn’t essential. I just thought it would look better that way. But a blind hole for the pencil might make it less convenient to adjust. Then drill a cross hole, close to the pencil hole but not intersecting it. Now make a saw cut to split the pencil hole down its middle. Go a bit past the cross hole so there is some spring in the wood. Fit a small coach bolt, washer and wingnut in the cross hole. When tightened, it will close the saw cut and pinch the pencil to stop it moving.
Smooth off any rough edges, drill a hole through both arms near the pivot so you can hang it up, sharpen the pencil, and your homemade compasses are finished.
pair of large homemade compasses
Large pair of homemade compasses

Posted on by — Leave a comment

Tips for copy turning

Inexperienced turners find copy turning quite intimidating. But making two or more pieces the same need not be difficult. After all, when you have turned the first you have proved your ability.

Copy turning attachment

A copy turning attachment for your lathe is one option. But it’s only really worthwhile if you have a great many items to do. The attachment must be paid for, set up and taken down, and may get in the way when not in use. It may not even save time. For most turners it’s probably better to save money and benefit from the practice that hand turning will give you. Soon you will be able to make duplicates so quickly that you will surprise yourself. Making lots of the same item is an excellent way of building your skills. You will find you can then make other shapes much more confidently and fluently. And why take up woodturning if you don’t want to do the turning?
When you make a set of turnings, they need to be very similar, both to each other and to the original pattern. But it’s rarely necessary for copied items to be indistinguishable. Slight variation is almost always acceptable, even desirable. It shows that the items are handmade. If you look at antique furniture you may well see minor variation in the spindles. It’s part of the charm of the piece. Of course, this is not an excuse for sloppiness. Generally, the closer together you place two items, the more closely they should resemble each other. At the other extreme, if the items are to be sold separately, a family resemblance may be enough.

Critical dimensions

The most important dimensions of a spindle being copied are usually the overall length, the maximum and minimum diameters, the diameter of any tenon or fitting, and the position of beads or other prominent features. The exact size or shape of beads, fillets and coves is not normally so critical. If one finished item does not stand out markedly from the others, the set is probably OK. But the tighter the specification, the more care has to be taken with measurements, marking out and the turning.

Tips for copy turning

It’s probably not worth attempting copy turning (unless you are doing it just for the practice) until you are able to produce beads and coves with reasonable reliability. Assuming you can do this, first make one complete item to your satisfaction. This proves that you can do the job, and is a sample that acts as a guide for the rest. Make a holder for it that positions it just behind the lathe so you can see it when working on the others.
When doing the rest of the items, it helps if you break the task down into steps and put all the items through each stage before going on to the next. The advantages of this are first that the practice gained from carrying out that step on the first item is immediately put to use on the next. Secondly, you can see as you go that each one is within tolerance. You should start with some spares to allow for any rejects along the way.
This is not the most efficient method of production, as you must spend time changing over the blanks. So with more experience you will probably complete each item before going on to the next. However, by working in small steps the turning is simpler, mistakes may be less likely, and you will soon become quick and confident at each stage.
You may have a motley collection of scrap wood to work with. If so, it makes the copying easier if you start by making the blanks identical. You will then have a stack of cylinders all the same size. Make them just slightly more than the maximum diameter of the finished piece to allow for sanding.

Marking out

Make a template by marking the key points from your sample onto a piece of thin ply. You can offer this up to the spinning blanks and mark circles on them with a pencil. The number of points and circles will depend on how accurate you want the copies to be. Usually, I mark the centre line of each bead, the position of any tenon and the overall length of the item. I don’t normally mark or measure the width of beads or hollows or fillets. This is partly because if there are too many lines drawn on the blank it is confusing and leads to errors.
If this is a job you will repeat in future, label the template, sketch the item on it with the marks for the key points in the right places, write the relevant finished diameters and size of the blank and put it somewhere safe.

 Prepare the tools

Sharpen and lay out the tools for the job. If possible, have enough pairs of calipers to make all measurements that you need – not usually more than three or four. Set them to slightly over the relevant finished diameters to allow for small errors and sanding. In softer wood the calipers can damage the surface, so if possible don’t use them right on the crown of  a bead. Calipers without lock nuts can open slowly in use, which is a common source of error. Lay them out in order so you don’t mix them up. You might label the calipers to correspond to the positions on the marking strip. With practice, you may find that you only need to use one or two pairs. You can judge other diameters by eye, using the measured diameters or sometimes the drive centre or tail centre as points of reference.
Use a parting tool to set the bead diameters with the calipers. When you have set the diameters, if the shape permits it, part in on each side to block out the beads, centred on the marked lines. With practice you will have the confidence to set the width and depth by eye. The parting cuts both locate the beads and make clearance for the gouge or skew. Sometimes there is no room for the parting cut, for example if there are two beads side by side. Then you will have to make V cuts instead with the skew or spindle gouge.

Turn the shape

When copy turning, turn the beads first, then the coves, then clean up the fillets. Measure if you need to, or if the size is critical, but try to set the width of any fillets and the depth of coves by eye. Aim to get all fillets on an item of equal width, and all coves and beads properly shaped. If you shape them properly, the finished dimensions should come out right each time. Pay particular attention to the shape of larger coves and beads and sweeping curves. Size the tenons, if any. Like many turners, I use a spanner to get the diameter right, cutting with a parting tool.

When you have finished the batch, line them up and pick out any rejects. If you need small sets, sort them into groups that match best. Here are a few spindles I made using these methods. They are part of a batch of 200. After sawing the blanks to size and turning the first three, the only measurements necessary were to mark the positions of the beads and to size the tenons. Because these spindles are small, I used multiples and fractions of the tool width to position the beads.

small spindles copy turned by hand

Posted on by — Leave a comment

New website

Until recently I operated a website at www.turnedwoodenbowls.com. Because of technical problems with it, I set up my new website here. I think it already looks and works better for visitors than my old one, which I have now closed. It’s easier to manage too, though I still have a lot of work to do on it. I haven’t yet republished all of my old posts, and I still have to transfer some images.

I have migrated my list of subscribers. So if you are one of them, you will be notified when I add new posts, and I thank you for your interest.

I’ve published a couple of new posts here so far, on sharpening and on dust extraction. More will follow, so if you haven’t yet subscribed, please do.

Most of the wooden bowls and other things on my product pages here are new. In due course I shall list stock from my old site here. If you are looking for a specific item, just let me know.

Posted on by — Leave a comment

Tapping a thread in steel is a useful workshop skill

This post is for people with little experience of working in metal. Tapping a thread is a useful workshop skill. It’s easy to cut threads in steel with a tap. You can use a drill and tap to fit a cutting bit to a tool shaft, assemble steel parts, or to make up frames for tool stands etc.

Drill the hole

Drill the hole for the thread using a tapping drill. This is just a normal twist bit the correct size for the particular thread. When drilling holes in steel, you need a bench drill with the speed set slow. This makes a hole that is square to the surface of the metal. When drilling metal like this it is essential to use a vice or clamp. The drill can catch when it cuts through, spinning the metal round and doing your hand no good at all.

The size tolerance is small, and accuracy is important. If the hole is bigger than recommended, the thread will be weaker, though the tapping will be easier. If it is too small, you will find the tap makes the hole bigger without getting a grip in the metal and cutting a thread.

The correct size of hole depends on factors including thread form and thread size. There are a lot of thread forms, such as Whitworth, BSF and BA, for which drill size tables are available online. I include here tables for the smaller metric threads and Whitworth threads that are commonly used in older machinery.

Taps

Taps come in all sizes and threads. You can identify the right tap to match an existing male thread such as a bolt by placing them side by side with the thread peaks lined up. Hold them up to the light, and you can see any mismatch further along the tap. If the diameter matches too, you probably have the right one.

Each thread type and size has three corresponding taps, though you don’t need all three for through holes. They differ only at the point. The first cut tap has a long taper to help start the thread, the second cut has less taper and the bottoming tap has none, because it works when the other taps have already made the start.

As well as the taps, you need a tap wrench.

Cut the thread

When tapping a thread, it’s necessary to align the tap accurately with the hole so that they are coaxial. A crooked tap will not produce a good thread. In shallow holes it is less critical, but the deeper you go the more severe any misalignment becomes, and the tap will break. The first couple of threads set the alignment. Don’t try to pull the tap straight once the thread has gripped the tap, it’s too late then. You can sometimes correct it by drilling the hole bigger at its opening and re-starting the thread further in.

A good way to start the tap squarely is to grip it in the chuck of the bench drill used to make the hole. That keeps it on track, but you have to turn it by hand, using the drill lever to keep gentle pressure on the tap so it enters the hole and starts self-feeding. Once the first cut tap is securely held by the thread it has cut, you can switch to the tap wrench. Just wind the tap in as far as it will go, taking care not to bend it. Small taps break easily. Then, if it is a blind hole, change to the second cut, which will go further in, then to the bottoming tap, which will complete the thread to the bottom of the hole. Before bottoming, clear out the swarf.

Another method for aligning the tap is to drill a clearance hole in a bit of scrap metal or wood and clamp it above the hole for the tap. The tap will slide through the clearance hole, which will hold it square. The clearance hole must of course be drilled square.

Lubricate the tap

Lubricate the tap to give a better finish to the thread. There are special compounds, but oil will do. The swarf cut by the tap has to be broken up as you go. To do this, advance a little then turn backwards a bit, going two steps forward and one back. If you don’t, the tap can get locked.

Blunt taps are hard to turn and may seize. You can sharpen them with a narrow, round-edge grinding wheel, but it is easier to replace them. Watch for this if buying second-hand taps, they were probably disposed of because they are blunt.

Metric tapping drill sizes

Tap                        Metric drill               Imperial drill

3 mm × 0.5           2.5 mm –

4 mm × 0.7           3.3 mm –

5 mm × 0.8           4.2 mm –

6 mm × 1.0            5.0 mm –

7 mm × 1.0            6.0 mm                      15/64

8 mm × 1.25           6.8 mm                      17/64

8 mm × 1.0             7.0 mm –

10 mm × 1.5            8.5 mm –

10 mm × 1.25          8.8 mm                      11/32

10 mm × 1.0            9.0 mm –

12 mm × 1.75          10.3 mm –

12 mm × 1.5             10.5 mm                    27/64

14 mm × 2.0             12.0 mm –

14 mm × 1.5              12.5 mm                    1/2

16 mm × 2.0              14.0 mm                   35/64

16 mm × 1.5                14.5 mm –

Whitworth tapping drill sizes

Size (in)                  Tapping drill size

1/16                          Number Drill 56 (1.2 mm)

3/32                          Number Drill 49 (1.85 mm)

1/8                            Number Drill 39 (2.55 mm)

5/32                          Number Drill 30 (3.2 mm)

3/16                           Number Drill 26 (3.7 mm)

7/32                           Number Drill 16 (4.5 mm)

1/4                             Number Drill 9 (5.1 mm)

5/16                           Letter Drill F (6.5 mm)

3/8                             5/16 in (7.94 mm)

7/16                           Letter Drill U (9.3 mm)

1/2                             Letter Drill Z (10.5 mm)

9/16                           12.1 mm (0.4764 in)

5/8                             13.5 mm (0.5315 in)

 

Posted on by — 14 Comments

Turning metal on a wood lathe. Small items are possible

Aluminium finial turned on a wood lathe

Turning metal on a wood lathe is possible, even though the wood lathe is not designed for it. Lathes are designed specifically for either woodturning or engineering purposes, rarely both. The tool holder of a heavily-built engineering lathe clamps the cutting tool firmly and moves mechanically. But if you don’t have an engineering lathe and aren’t too ambitious, you can turn small items in brass, aluminium or even steel freehand quite successfully on a wood lathe. I turned the aluminium finial shown above on my Graduate Shortbed lathe, mainly using a small gouge, cutting as if the metal were wood. I threaded the finial onto a bit of 12 mm studding held in a chuck. Even with tailstock support, that was not rigid enough, so I had to sand it to an acceptable finish. It is about 5 inches tall.

There are problems to overcome. Holding the tool in your hand so that it cuts steel is difficult. The hardness of the metal resists the cut, and the cut is very liable to ‘chatter’. This is vibration that leaves a rough or ridged surface on the work. Working freehand, accuracy is harder to achieve. Some wood lathes have a proper slide rest as an accessory, but without that accuracy comes from the turner’s skill. Making true cylinders or flat surfaces accurate to a thousandth of an inch freehand is not easy. But many items don’t need such precision.

Interrupted cuts, such as turning the corners off square stock, are particularly difficult freehand because it is hard to control the cutting tool. It is risky, too.

Preventing chatter

Woodturners are familiar with the problem of chatter. When turning metal on a wood lathe it is hard to avoid. To prevent chatter, you need a strongly built lathe, with good bearings. It must hold the workpiece firmly. The workpiece must be stiff, or well supported, so it doesn’t flex. That means minimum projection from the headstock. For example, modifying a drive centre while it is in the spindle taper is easy. A similar job held in a chuck is harder, because the metal can move away from the cutting tool.

Use tailstock support whenever possible. A Jacobs chuck will hold small items. Light cuts using a robust and sharp tool, with minimum projection over the toolrest, should then produce an acceptable result.

The tools

You can use a high speed steel woodturning scraper or a graver. A graver, which you can easily make yourself, was traditionally made from square section tool steel with a diagonal flat, leaving a long point at one corner. You could convert a triangular or square file, but a high speed steel tool bit would be better. A round high speed steel bar ground with a pyramid point would work. It would be similar to a woodturning point tool, but with a more obtuse point. Use a graver a bit like a skew chisel. Its edges (not the point) can plane off long, thin curly shavings from steel.

Brass likes tools with zero top rake, so responds well to scrapers. Tools leave a polished surface on brass. Aluminium turns with a graver or even a small short-beveled bowl gouge. Cutting speeds are lower than for wood, but because only small items are possible, the normal low-speed setting on the lathe is probably OK. Some metal alloys are more free-cutting and ‘turnable’ than others. A file will shape the item and remove chatter marks if necessary. Even on a lightweight lathe you can make simple shapes (for example putting a pointed end on a short bit of rod) in steel using a file, an angle grinder or a rotating grinding wheel held in a drill chuck.

Turning metal on a wood lathe is tiring, particularly with steel, because the tool must be held firmly up to the work. It helps to use a pivot pin in the toolrest to lever the tool into the work. This gives more control. If the workpiece is held rigidly, the pivot pin can help prevent chatter too.

Safety when turning metal on a wood lathe

Turning metal freehand is hazardous, therefore precautions are necessary. It is essential that the workpiece is secure in the lathe. Chunks of metal flying out of the machine are even more likely to do you harm than are lumps of wood. Eye protection is a must. The swarf is sharp and hot – wood chips hitting your hand are annoying, but metal swarf can cut or burn. Long strands could even catch your fingers and drag them in. Never clear away swarf while the lathe is running.

Turning with a scraper can make chips like little needles. They can get in your skin like splinters. But gloves are risky around moving machinery because they can catch and drag your hand in. Thin ‘rubber’ gloves that can easily tear are safer. A bad dig-in could wrench the cutting tool hard enough to break it and perhaps cause injury. A file thrown back by the chuck jaws can injure you. Tools must always be used with a proper handle to stop the tang impaling your hand.

Posted on by — Leave a comment

Don’t forget dust extractor maintenance

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 been meaning 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, long ribbons of plastic had passed through the cyclone and blocked the grid. It was surprising that air could get through it at all.

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 a problem like this. 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. An objective way to measure suction would be useful. I shall have to consider a vacuum gauge.

Shavings trapped in dust extractor fan guard
Waste trapped by fan guard
Posted on by — Leave a comment

A homemade centre finder is easy to make and quick to use

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.
The centre finder I used for a long time is simply a small wooden block. The block has a hole drilled that is a push fit for a short 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.
pencil block centre finder
Pencil block centre finder
adjustable centre finder
Adjustable centre finder

I’ve now made an 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.

To find the centre of a bowl blank, I usually use a hardboard disc of appropriate 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.
chuck insert centre finder
Chuck insert centre finder
When I need more accuracy, I use a chuck insert centre finder. This is a short dowel with a steel point in one end. I turned the insert to fit inside the body of my engineering chuck. I put the chuck on the bench and adjust the jaws to be a sliding fit on the spindle blanks. The blanks must be square or cylindrical. A tap on the end of the blank pushes it onto the point to mark the centre. This is a good method to use when part of the finished item needs to be left square.
Posted on by — Leave a comment

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

Lots of woodturners fear the skew chisel. Skews dig in alarmingly, seemingly without any warning or provocation. Some people don’t use them at all. But can you really call yourself a woodturner if you can’t use a skew chisel? It’s perhaps  the most useful and versatile 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 it.

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 a diamond hone. But it’s OK to use either a straight edge skew chisel or a curved one straight from a grinder. Platform sharpening is probably the easiest method. 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. You must grind away the sharpness from the long side edges of the tool so they slide easily on the tool rest. Nowadays you will probably find this has been done at the factory if you buy good quality tools.
If possible, use a strong, rigid skew chisel of about 10mm square to practice beads (dealers sell these as ‘beading and parting tools’. You can easily grind it 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. Put on your face shield, just in case. Later you will probably want to use higher speeds.
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. A ring centre will also drive the work safely, and doesn’t need a pilot hole.

Practice

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 or thin ones whippy, neither of which is helpful. Choose a blank that is straight-grained and without knots.
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 skew 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.

 Rough out the shape of the bead

The first few times, use a scraper to make a shallow 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 its proper cutting position as you go. The chisel will begin almost flat on the rest and twist over. After you have made some shallow beads, try some that are fully semicircular. On these, the tool will 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 muscles begin 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 round the roughed-out bead. 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. 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, correct it with the scraper or 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 sweet spot 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 pay attention to keeping the bevel in contact and 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 practice steering the cut to round over the end – this is another good way to make beads.
Posted on by — Leave a comment

A ball cutting jig can be made from a 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 or don’t want to do them freehand, you can use a homemade or commercial ball cutting jig. I make lots of balls in a range of sizes, and for me a jig that lets me produce them quickly and accurately is essential.
The most basic ball cutting jig 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 just 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 component is a machine slide such as top slide from a metal turning lathe. These can be obtained from dealers in old tools, or from Ebay. You might also find something suitable from Banggood, who sell inexpensive machine components, including compound slides for metal lathes. 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 lathe and machine slide you have so I can’t give more than guidance. Assembly would probably only involve drilling, tapping and bolting together.
homemade ball cutting jig
Jig set up on Graduate shortbed lathe
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 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 steel with a tap by screwing it into the correct size hole.
The ball cutting jig (see cross-section 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 (not shown on plan) 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 plate 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 plate and slide platform are all locked together with the pivot pin. This could 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 plate 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 unthreaded 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.
limiter for homemade ball cutting jig
Lock nuts limit 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 homemade ball cutting jig
Tool holder
 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. Pull the slide round to make a cut, then advance the tool for the next cut. When set up, I can very quickly make lots of identical half balls.
hemisphere cut with homemade ball cutting jig
MDF hemisphere cut with homemade ball cutting jig
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 cutting jig
Posted on by — 5 Comments

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 can be used for spindle turning, though not very convenient for this, 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, being open at the back. 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 shortbed lathe
Graduate shortbed lathe showing unusual tailstock and crossed slots in bed.

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.

Both 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. 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. Any of these bowls could have been made on the Graduate. 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.