Posted on

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 is 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 is 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, a 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. Many turners 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. After sawing the blanks to size and turning the first three, the only measurements necessary were to mark the positions of the beads using a marking strip and to size the tenons.

Copy turning spindles
Six copy-turned spindles
Posted on

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

Turning metal on a wood lathe. Small items are possible

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. Heavily-built engineering lathes work better than wood lathes. Their tool holder rigidly clamps the cutting tool and moves mechanically. But if you don’t have an engineering lathe and aren’t too ambitious, you can turn many small items in brass, aluminium or even steel freehand quite successfully on a wood lathe.

There are problems to overcome. Holding the tool 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. Without a tool slide, 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 something, are particularly difficult freehand because it is hard to control the cutting tool. It is risky, too. Some wood lathes have a proper slide rest as an accessory.

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, with 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 in steel using a file 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. A heavy cut can increase it.

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. 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 tear are safer. A bad dig-in could wrench the cutting tool badly enough to break it and perhaps cause injury. A file thrown back by the chuck jaws can injure you. They must always be used with a proper handle to stop the tang impaling your hand.

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

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. Many of my bowls could have been made on a small lathe, but not all. 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

Mobile bases make more space in the workshop

My workshop, like yours, could do with more space. I am at or beyond the point where if I want anything new I first have to work out whether I can fit it in. To make things more manageable, I recently fitted mobile bases to some equipment, including to some big racks I built for materials and part-finished work. These items now live in the corners and get pulled out when needed. I have clear workspace in the middle. Luxury!

Commercial bases

The first of my mobile bases was a commercial one for my table saw. It worked well enough to encourage me to go further. The second and third were pairs of rollers of the kind used for kitchen appliances, which I put under the bandsaw and the router table. They were much less successful as they don’t steer easily and tend to get out of place. Also, their very small wheels tend to get stuck when there are shavings on the floor. I plan to replace them.

Homemade bases

My next move was to get some heavy-duty casters and build my own mobile bases. They are much less expensive than the commercial bases, just as useful, if not more so, and much better than the appliance rollers. The simplest construction is a square of plywood for the item to stand on, with a caster under each corner. But suitable casters are several inches in height and may make tools too high for easy use, and less stable.

A different construction method can keep the equipment close to its original height, at the cost of putting the wheels outside the item’s footprint. This is not necessarily a problem, and it does make the item more stable. The casters fit under the ends of a pair of cross beams, either timber or angle iron. The beams go next to the unit, not under it. The item stands on a plywood square. But the plywood is wide enough to hang from the underside of the cross beams, between the casters. Spacer blocks between the beam and the plywood drop the plywood platform close to the floor. The increased overall height is then just slightly more than the thickness of the plywood.

Casters

I found that swivel casters on all corners are the easiest to use for fully mobile bases as they let the item turn on the spot. The casters need enough clearance to swivel without hitting anything. They do tend to resist changes of direction a bit when the wheels are facing the wrong way. This can make a simple pull out and push back movement harder. If that is all that is needed, fixed casters might be best. They are self-steering for that situation, but of course are harder to manage when out in the workshop. Larger wheels roll more easily if the floor is uneven or has shavings on it. I find they don’t need brakes, unless perhaps if the floor is super-smooth and clean, or sloping. Wedges slipped underneath the item stop it moving. If a mobile workbench or machine will need to resist sideways forces, you will have to stabilise it. You would need to wedge it carefully to lift the wheels clear of the floor. Brakes on the wheels would have to act on the swivel as well as the wheel itself. So I suspect they would be less effective than the wedges.

There are plans available for trolleys that lift the item for moving and let it down again when in place. These would be best for stability and convenience, but are more complicated to build.

I tried casters with a single fixing bolt and the kind with a steel plate that you fix to the beam with screws or bolts. I think the plate fixing is easiest for fixing to plywood or timber.

Posted on

Braking a grinder can speed up batch tool sharpening

If you sharpen turning tools with a grinder, you can set the adjustable platform to suit the grinding angle of the tool. But each kind of turning tool needs a different angle, so you may find you are continually re-setting the grinder platform. I have written about some simple jigs that make this accurate, repeatable and easy to do. But my grinder takes a long time to run down after switching off. I can’t use my setting jigs until the wheels have stopped. I wanted a way to stop the machine quickly to grind several different tools at the same time. But braking a grinder could either clog the wheels or cause unnecessary wear. There is a simple solution.

A rubber block of the kind sold for cleaning sanding belts pressed against the rim of the wheel will bring it to a stop very quickly. It leaves no significant residue on the wheel – if anything, the wheel is cleaner afterwards. The rubber gets worn away, but it will last a long time.

Risks when braking a grinder

There are two points to keep in mind. Braking a grinder too quickly could cause the wheels to loosen. Braking forces applied directly to a wheel will tend to tighten it, just as normal grinding does. But the inertia of the other wheel might make it over-run and loosen its retaining nut. This could allow the wheel to spin freely on the spindle and perhaps even come off. The wheel guards must stay in place, and the nut kept properly tight. I am confident that, if the wheel ever comes loose on my grinder (it hasn’t happened yet!), the guard will stop it coming off the spindle. If you don’t have that confidence, please allow your grinder to slow down in its own time.

The other risk is rubber particles accumulating in the wheel shroud. Grinding sparks could possibly ignite them. Again, this has never happened with my machine.

Posted on

Grinding short gouges

During the years that I’ve been turning some of my tools have got shorter. Each grinding takes off just a little bit of metal and it adds up. I have never yet got to the end of a gouge or scraper. But there comes a time when grinding short gouges with a jig gets difficult.

Different jigs have different ways of clamping a gouge. Some have a peg that fits in the flute and some have a flat plate that bears on the sides of the flute. Either way, the jig has to lock the gouge in place and align it properly.

Modern gouges tend to have short flutes. This is a good thing, because it makes the tool more rigid. But if the jig clamp acts on the flute itself, how do you use it when there is not enough flute left to give the proper projection in front of the jig? When the flute gets short, the tool may have plenty of life left in it. But the jig clamp begins to bear on the up-sweep at the end  of the flute, and then later on the round surface of the shank. It no longer grips securely or aligns the flute properly.

There are several ways to overcome the difficulty of grinding short gouges. You can reduce the projection of the gouge from the jig, but this changes the bevel angle. You can learn to sharpen freehand – a nearly worn-out gouge is a good tool to practice with. Or you can re-shape the shank to suit the clamp. This is what I did today on two of my favorite bowl gouges. They were originally shallow fluted spindle gouges that I ground with a short bevel and round nose. They work really well for making small wooden bowls that aren’t too deep.

I ground down the upper surface of the shanks, leaving them flat and at the same level as the top of the flute sides. This would be enough for some types of jig, but mine is a Tormek jig that I use on the high-speed grinder. It has a small projecting peg under its clamping plate. So I mounted a metal-cutting wheel from an angle grinder in the lathe and carefully ground a groove along the middle of the flat part. I can now carry on sharpening the gouge as before, getting a lot more use from these two tools.

Scrapers

When scrapers get short, the handle starts to foul the platform rest at the grinder. To overcome this, you can make the platform smaller and cut off its corners so the tool can swivel for sharpening. Another option is to make a secondary platform that clips on the main one. Make it smaller, and thick enough for the tool handle to pass over the lower platform unobstructed. The secondary platform should be easily removed. If the lower one is steel, you might be able to use magnets, but they would attract the grinding dust. I use a bit of plywood with a length of perforated steel strapping as used by builders. This slides over the main platform. You have to alter the platform angle to allow for the extra height.

Posted on

Profile gauge helps make better bowls

A profile gauge is an inexpensive device with sliding pins that are pressed on a surface to copy its shape. They are occasionally useful for general DIY, but have a use in woodturning too. The obvious use is in copy turning, when they make a template to exactly match the shape of a curve on two items. I have had one in a drawer for many years without using it very often. But I recently started getting it out a bit more often to use as a teaching aid.

A profile gauge shows the curve

When making bowls it is important to get good curves on the walls and bottom. I am a bit of a perfectionist and go to a lot of trouble to get them right on the bowls I sell. You can see the outside profile of a bowl easily enough. But the interior is more difficult, both to turn with the necessary accuracy and to see the shape. If the bowl is small enough, your fingers will tell you when you have it right. What you can see and feel is normally all that really matters in the finished bowl. But when the bowl is too big for your fingers to reach to the middle, you must rely on sight and/or calipers. Sometimes mistakes are missed during the turning. They show up later when the bowl is off the lathe and polished. They can spoil the piece.

Now I sometimes use a profile gauge to show the student in my woodturning classes how the shape of a piece is developing. The profile gauge shows the curve in two dimensions instead of three. Any flats, dips and bumps can then easily be seen. They are especially useful for the shallow curve in the bottom of the bowl, where the gauge will clearly show if there is a bump or dip in the middle. The best kind to get is one with thin metal pins, not thick plastic ones without the resolution needed.

Profile gauge
Profile gauge
Posted on

Ball making jig can produce half-round hollows – Woodturning by Terry Vaughan

I normally use my homemade ball making jig like everyone else does, to make balls. But I also make hemispherical hollows. Today I started work on some small boxes that will hold globes, mounted so they can spin in their box. I used lignum vitae reclaimed from old bowling woods.

When the ball making jig pivots, the cutter travels through an arc. It makes either a ball or a hollow. It depends where the cutter is in relation to the timber and the jig’s pivot point. When the cutter is directly above the pivot point, it doesn’t move. To cut a hollow with the jig, I just have to advance the cutter past the pivot point. The pivot axis is set a little inside the plane of the box rim. Then I can later mount the globe a little below the rim. Swiveling the jig then cuts the hollow very accurately so it fits the ball nicely. Lignum vitae is very hard, and gritty cracks in the wood blunt the cutter. A round nosed tungsten carbide tip brazed to a steel shaft stood up to it.

Setting up the ball making jig

Once set up, the jig works well, but it is not as easy to set it up for hollows as it is for balls. The principle is straightforward. But the cutter shaft and tool holder tend to foul the blank when they are cutting at the box rim. The trick is to align them so they clear the blank but the tip finishes its arc at the centre of the hollow.

The cutter needs room to work, so a very stout tool is only possible for large hollows. Fortunately, that is where rigidity is most essential. In order to use a reasonably robust tool, I made a couple of gouge cuts at the beginning. This started opening up the hollow and made room for the cutter. I could have drilled a pilot hole instead.

When the box bases and domed lids all have their hollows, and the corresponding balls have been shaped, the work with the ball making jig is finished. But there is still some turning to do, shaping and fitting each box and its lid. I shall do this after the holiday. I have to fit the axis pins to the balls, and they will later have the map gores applied. But that happens after they leave my workshop.

Posted on

Grinder platform angle setting jig

Sharpening is one of the essential skills for woodturning. Most turners use a grinder to sharpen tools, and platform sharpening is probably the best method for skews and scrapers. But each type of tool needs a different grinding angle, so a grinder platform setting jig for each angle is very helpful. For example, a skew chisel will usually have a more acute angle at its edge than a spindle roughing gouge, which in turn will have a finer edge than a scraper.

Each of these tools can be ground while flat on either the grinder’s own tool rest or a separate platform rest, which just has to be set to the correct angle. One way to do this is to blacken the existing tool bevel with a marker pen then adjust the platform until the bevel comes into full contact with the wheel, which is inched round by hand so that the ink removed will show the accuracy of contact. Or you can just match the bevel to the wheel by eye, looking from the side. But in either case, any error can be cumulative. It will be repeated and possibly amplified next time the tool is ground. This can lead to a gradual change in the bevel angle.

I use an easy-to-make grinder platform setting jig that gives a consistent, repeatable result very quickly. It consists of a scrap of plywood with two projecting screw heads that align it to the wheel rim, and a straight edge at the bottom to which the platform can be set. The jig is very easy to make and use. A different one is needed for each tool type and thickness (thicker blades contact higher on the wheel rim and because of its curvature will be ground to a sharper angle than thinner ones). Use plywood thick enough to take the screws in its edge without splitting, but no dimensions are critical. All you have to do is set the platform angle as you wish, perhaps copying an existing tool angle, then cut the plywood so it rests on the platform with its edge fairly close to the wheel rim. Insert the two woodscrews (as far apart as the wheel guard and platform will allow, and angled so they are radial to the wheel axis. Drill pilot holes to prevent splitting.) The screws are optional, but if used, they can be turned in or out to fine tune the fit or to compensate for wheel wear. If necessary, the inner edge of the plywood can be cut away to follow the wheel rim more closely.

To use the grinder platform setting jig, loosen the platform, place the two screw heads in contact with the stationary wheel rim, bring the platform into contact with the bottom of the jig and tighten up again. Every time you sharpen the same tool, or another of the same blade thickness, the angle will be just the same, making for quick results and saving tool life.

Grinder platform setting jig

 

Posted on

Wet sanding is messy, but prevents dust and clogged abrasive

I recently did some wet sanding to improve the surface of some sycamore bowls that already had a Danish oil finish that had dried a bit rough. I used fine ‘wet or dry’ abrasive with white mineral spirit as lubricant and got some good results. After wiping clean, the surface was silky smooth. I applied some more finishing oil afterwards and they are now ready for buffing. Today I have been making some lignum vitae boxes out of old bowling balls. Lignum vitae is a very hard wood with a waxy content that clogs sandpaper like the dried oil finish on the sycamore bowls. I tried wet sanding here too, using water this time. I just held a wet bit of kitchen paper to the freshly turned surface at the same time as the abrasive. You could use a spray bottle. The result was lots of mud that sprayed off and made a mess of my turning jacket, but a very good surface was quickly achieved on the wood. No dust and no clogging. I started at 180 grit, then 240, and finally 320 which gave a fine matte surface ready for further treatment. It is important to use good quality abrasive, particularly if using ‘wet or dry’ silicon carbide paper. The cheap grades tend to shed particles and leave black specks embedded in the wood surface.

It was club night at my turning club last night. There was an interesting demo of making a spalted birch log into a hollow vase. The wood was very poor – I would have thrown it out – with advanced spalting and terrible tear-out. But the finished product was surprisingly good. The demonstrator used lots of quick-drying cellulose sanding sealer to harden the fibres before final turning to shape. Sanding with an unpowered rotary sander made lots of dust but left a quite reasonable surface.