'Workholding Methods' Or How to Mount Workpieces on the Lathe So That You Can Get at the Areas You Want to Turn

Workholding Methods

Tonight we are going to talk about 'Workholding Methods' or how to mount workpieces on the lathe so that you can get at the areas you want to turn. This is something that we touch on at nearly every talk or demo but tonight we are going to concentrate on just this aspect of turning with a bit of talk, a few demos along the way and hopefully some contribution from you. Much of this may be well known to many of you but with a bit of luck you will find something of interest.

I'm going to use the standard division of turning into Spindle turning and Faceplate turning just to separate things out a bit. Remember this is based purely on the grain direction of the workpiece but the grain direction does affect the pros and cons of various workholding techniques. In Spindle Turning the grain of the workpiece runs parallel to the lathe bed, while in Faceplate turning the grain runs at right angles to the bed.

Spindle Turning

Between Centres

When you say 'spindle turning', this is what most people would think of first – where the work is held between a drive centre at the headstock end and a supporting centre at the tailstock end. The headstock and tailstock are made to a specific tapered shape inside called a Morse Taper. This comes in several sizes indicated by a number – small lathes may have a No.1 Morse taper, most other woodturning lathes have No. 2 Morse taper. The centres are slid into the headstock or tail stock and engage to drive or support the work purely by friction.

Most headstocks and tailstocks are hollow so that you can use a knockout bar to remove a centre – but not all. If the headstock is not hollow, such as the Club Axminster M950 lathe, it is a good idea to use a centre ejector (also called a thread protector). This is screwed onto the lathe spindle before you insert the centre, then when you want to remove the centre you unscrew the centre ejector which pushes the centre out.

4 prong, classic drive for spindles, range of sizes from small 1/4” to large sizes 1 1/2” (show examples), good when end of workpiece is square to the length.

To mount a workpiece, make a dimple where you want the point of the centres at both ends– on small or irregular sections such as branchwood, you can do this by eye quite accurately. If the section is square you can draw in the diagonals and find the centre that way. Another idea is to set a marking gauge to slightly less than half the thickness, then scribe across the end from each side in turn. This will give a small square within which you can eyeball the centre. The square tapered type of bradawl gives an accurate hole.

Locate the pin of the centre in the mark, hold workpiece and centre in a straight line and tap the end of the centre with a soft faced hammer so that the dogs cut into the workpiece. Do not use a steel hammer for this as this will marr the end of the centre and prevent it seating properly in the Morse Taper. Good idea to mark the drive centre, and the end of the workpiece so that, if you remove the work from the lathe, you can replace it exactly. I file a small notch on one of the dogs.

To mount the workpiece insert the centres into the Morse tapers, locate the workpiece onto the drive centre, then hold it in line while you move and lock the tailstock into position. Wind in the tailstock barrel so that the workpiece is supported and held against the driving dogs. Excessive pressure is not necessary and can cause a number of problems, especially as the workpiece becomes thinner as it is shaped.

Keep the point and the dogs sharp. Put the centre into the lathe and run at a moderate speed then hold a fine file against the point to sharpen it and keep it true. Touch up the dogs with a file or very lightly on a grinder being careful to maintain the original bevel angles.

Stebcentre - newish design, now made and marketed by Robert Sorby. Consists of a circle of small teeth surrounding a spring loaded centre pin. Available in a range of sizes from ½” diameter to 1 ¼” , MT1 and 2. Versions available to be held direct in chuck jaws, designed for Patriot and Supernova chucks. – check that it will fit your chuck. Also revolving versions for use in the tailstock. To use, mark the centre point as usual, locate central pin in the mark then wind in the tailstock to push back the pin and engage the teeth. Gives a good grip. You can remove and remount work without loss of concentricity. I don’t like using a Stebcentre for very thin work because of the pressure needed to engage the teeth. other drive centres Lace bobbin drive – will drive any small square blank Light pull drive – drives from the bottom end, centred on the through hole and drives via the hole for the cord knot (show picture from catalogue). Home made – my blind pull drive, like a light pull drive. Cone drive or fruit drive – will drive a round shape without marking. You can use a tailstock dead centre as a drive in the headstock, either cone or ring type. Counter bore drive – used after you have bored a hole right through the workpiece The pin locates in the hole and the dogs drive the work.

Tailstock the tailstock centre supports the other end of the wood as it rotates. Years ago you used a ‘dead centre’ which did not rotate and had to be lubricated to stop the timber burning. Now we all use a revolving centre which has bearings that allow the centre to rotate with the work. The standard version is the 60° (show examples) but there are other variations. The ring centre (show example) is useful where the timber may be split by a standard centre and it is easier to adjust the position of a ring centre.

A hollow ring centre is used when long hole boring to allow the auger to pass through into the wood. Bore the hole then insert the tip and centre the tip in the bored hole.

Multi head revolving centres – lots of these sets in the catalogues – browse your favourite catalogue!

Centres available from all the usual suppliers in MT1 or MT2. Adaptor sleeves are available to enable you, for example, to use an MT1 centre in an MT2 lathe (show examples).

Other ideas You could insert a suitable sized blank direct into the headstock Morse taper. Tap it in gently to seat fully. If your headstock is not hollow this might not be a good idea !

As a refinement of this idea you could turn a Morse taper between centres then insert this in the headstock and continue work, preferably with tailstock support to keep the Morse taper engaged (show my pen assembler as an example).

If you have a Jacobs chuck on a Morse taper you can insert this in the headstock and use it to grip workpieces. Take care when tightening the chuck as it is easy to crush wood in a Jacobs chuck.

You can use a scroll chuck fitted with suitable jaws, with or without tailstock support. I use a chuck fitted with pin jaws, which we will talk about soon, for the second stage of making mushrooms.

Screw chuck and jam chucks – we’ll talk about these in the next section as they can be used for both types of turning.

Home made spigot chuck – hold a suitable piece of hardwood between centres, turn to round, face off one end and cut a spigot to fit your scroll chuck jaws. Remove wood, mount scroll chuck, hollow cup shape to fit the work you want to hold. Make saw cuts down the walls of the cup to give flexibility, fit Jubilee clip to tighten the chuck. Good for finishing fruit and eggs.

This is typically bowls, dishes and platters but much of what follows can also be used for a workpiece that is technically a piece of spindle turning e.g. when making a vase.

Let’s talk about chucks. When woodturning began to take off in the 1980’s a variety of sometimes weird and wonderful chucks were developed and marketed. Most of these have now disappeared in favour of woodturning versions of the 4-jaw engineering scroll chuck. The scroll is a steel spiral thread largely hidden inside the chuck body (show end of scroll). The jaw carriers have teeth on the underside that engage with the scroll so that as the scroll is rotated by means of the chuck key, the jaw carriers move in and out. The jaws are mounted onto the jaw carriers, usually with socket head screws that have an Allen key recess. Thus the jaws can easily be removed and another set screwed onto the jaw carriers.

Different lathes have different sizes of spindle thread, depending on the size and capacity of the lathe itself, in both Imperial and Metric measurements. It is not economic for chuck manufacturers to make and hold stock of say, 20 different chucks. Most chucks have a standard thread in the chuck body into which an insert is fitted. The insert carries the female thread for a specific spindle thread type. Thus you have one chuck and 20 inserts. (show example of club Patriot chuck with 2 inserts)

Some, mainly larger, chucks achieve the same flexibility by means of a detachable threaded backplate (show Versachuck).

When deciding which chuck to buy it makes sense to look at the range of jaws available for each chuck and decide which jaw range best fits the type of work that you think you will want to do. We will look at some of the jaws available for the SuperNova chuck which will also fit the Patriot. (show how the jaws are located on the jaw carriers, using carriers from the Versachuck, explain the concept of the Versachuck).

Pin jaws – designed to expand inside a 1” hole and grip an irregular blank, also has a small dovetail to grip a recess, and will grip a long spigot, very useful.

2” or 50mm jaws – standard size that you get with most chucks. Jaw profile varies somewhat, SuperNova is good, Versachuck ones less good. Up to about 10” diameter bowls. step jaws – three ranges of diameters from one jaw set. I thought they would be useful but the shape of the bowl is compromised if you want to use the inner steps so they are not as useful as I hoped. long reach jaws – very useful for reverse chucking a deep bowl for final turning. Think back to Easy Bowls Part 2. spigot jaws – much deeper than the standard 50mm jaws with grooves that bite into the spigot when you tighten the chuck. Used for vases and hollow forms. I’ve turned 16” high vases with these. No external dovetail.

100mm jaws – larger and deeper than 50mm jaws. I’ve turned 20” diameter dishes using these.

Powergrip jaws – a cross between the spigot jaws and 100mm jaws. Use for large vases and hollow forms.

Any other jaws that anyone wants to mention ?

If you change jaw sets regularly it’s a good idea to buy a proper long Allen key.

Face Plate – classic way to mount a workpiece but still the strongest. Face plate screws direct onto the lathe spindle. Very easy and quick with modern screws and a powered drill/driver – just drive straight in. Use as many screws as you think necessary. Ensure that the screw holes will be turned away in the final piece, if necessary use packing to reduce the penetration of the screws.

Face plate ring – a metal ring with a dovetail recess to take the chuck jaws which you attach to the workpiece with screws. Not as strong as a face plate, possibly better suited to mounting bought blanks that have a smooth surface. Very useful for mounting home made gadgets such as a sanding disc, reversing pad etc. (show examples)

Screw chuck – most scroll chucks come with a screw chuck that can be held in the chuck jaws. Originally screw chucks used a standard wood screw, then coach bolts, then the parallel shank screw was developed. This must have a pilot hole of the correct diameter drilled first. Put the chuck on the lathe, insert the screw into the jaws and tighten. This is one situation where you should really tighten the jaws. Offer the drilled blank up to the screw and revolve the lathe spindle to draw the blank onto the screw. This is easier than trying to turn the blank round. Tighten until the blank is sitting snugly against the chuck jaws but no more or you could strip the thread in the wood especially in green or spalted wood. between centres – this is useful for natural edge and other irregular items. Use a large drive centre and a revolving centre in the tailstock. You can create a drive centre by grinding a point on three suitable bolts then bolting them through the holes in a faceplate at 120° intervals. The advantage of between centres mounting is that you can easily adjust the mounting points to balance the edge profile or whatever which would be much more difficult if you had screwed on a faceplate for example.

Interior turning briefly review the spigot vs. recess debate If you don’t have a scroll chuck then you can make a jam chuck or paper/glue sandwich, even double sided tape can be useful.

Reverse chucking

This is re-mounting a piece to work on the base area, typically to re-shape or remove the spigot used to hold the piece for shaping the interior.

Jam chuck – show example scrap timber held on a face plate ring. Form recess or spigot to grip the piece externally or internally. Bring up tailstock for safety if you wish, a ring centre with a pad between centre and work is less likely to mark the work. Still very useful and has lots of applications e.g. jam chuck a box on the waste remaining in the chuck to turn the base.

Cole jaws – many makes of chuck have these as an option.

Wood plate jaws – available for many makes of chuck. They enable you to mount a home made set of wooden jaws to greatly extend the diameter that can be held. Show and describe my example

Longworth chuck – a more sophisticated version of wood plate jaws. Instructions were in Woodturning magazine Issue 212.

A cheap and effective method is to mount a scrap of ply, MDF or timber on a face plate ring, spigot or recess, turn it to a general rounded shape then glue on a piece of router mat or similar padding. Place the bowl against the padding and bring up the tailstock to hold it in place. Turn away the spigot, re-shape the base or whatever leaving a small pip round the revolving centre. Remove this off the lathe by carving or sanding.

Vacuum chucks – expensive. Hollow cup with rubber rim mounted on the headstock, vacuum pump © Galloway Woodturners October 2011 Page 4 of 5 connected on the outboard end of the hollow spindle creates a vacuum to hold a workpiece against the chuck giving free access all round.

Any other ideas ??

A home made screw chuck can be useful and can be made in lots of ways. Anything that holds a suitable screw firmly and centrally should work.

To turn small bits of precious wood, face off a piece of scrap timber then glue the work piece in place with superglue.

A mandrel is typically used for turning pens but can also be used for anything that has a suitable sized hole through the middle.

We could go on for ages, I’m sure there are loads of other ways of holding work but that lot should get you started !!!