Make a Donut Chuck

I needed to make a donut chuck so that I could mount a 12″ bowl on my lathe and finish off the bottom of the bowl. I have a set of cole jaws for my jaw chuck, but they will only expand 10″.

You can click on any of the images to see a larger version.

The first step was to take a 16″ x 16″ x 3/4″ piece of plywood and find the center. I marked out three circles of 9″, 15″ and 15 3/4″ diameter. I laid out eight points on the 15″ diameter circle and drilled 5/16″ holes and inserted 1/4-20 tee nuts at each of these points.

I took another piece of 16″ x 16″ x 3/4″ plywood and placed it below the first piece. Using a transfer punch, I transferred the centers of the eight tee nuts to the second piece of plywood and then drilled 1/4″ holes at each of these points. I bolted the two pieces together using 1 1/2″ 1/4-20 bolts and cut the two pieces of plywood round, just outside of the 15 3/4″ circle. I used my jigsaw to do this as the workpiece would not have sat flush on my band saw table and I did not want the heads of the bolts to scratch my band saw table. As an aside, I used the new Xtra-Clean (T308B) blades from Bosch and was impressed at how easily they cut and how clean the cut was on both the top and bottom of the plywood.

Using my center finder I located a face plate I have dedicated to this donut chuck and attached it securely to the first piece of plywood.

I mounted the face plate and plywood pieces on the lathe and turned both pieces perfectly round. I marked a 9″ diameter circle on the front piece and drilled a 1/.4″ hole through both pieces using a drill chuck in the tail stock. I took the piece of the lathe and drilled a 5/16″ hole 3/8″ deep in the back piece of plywood and inserted a 1/4″ tee nut in that hole. Then I bolted both pieces together suing another 1 1/2″ 1/4-20 bolt.

I remounted the piece on the lathe and made a mark on the sides of the plywood pieces to help align the two pieces. Using a parting tool, I cut the 9″ diameter circle out of the front piece of plywood. I cut at an angle from the center out and took care to make sure I did not cut too deeply into the back piece of plywood. Because of the tapered cut and the center bolt the internal circle did not come loose. I had to remove all 9 bolts to take it out.

Lastly I cut a piece of high friction router pad cloth and using spray adhesive attached it to the inside face of the front section. This will help to both hold and protect the surface of the bowl.

The tee nut inserted in the center of the back piece can be used to mount a scrap piece of plywood to. A tenon that matches the internal diameter of a bowl can then be turned onto that scrap piece enabling you to mount the bowl in the donut chuck directly on center.

In my excitement at how easily the bowl mounted and how smooth and true it ran, I forgot to take a picture of the mounted bowl before I finished off the bottom. Here is a shot of the bowl mounted in the donut chuck, with the bottom finished and sanded.

Make Your Own Buffing Wheel Mandrel

Instead of buying an expensive mandrel for buffing and grinding wheels, I decided to make one for very little cost, or time involved, for use on my Wilton mini-lathe. In about 45 minutes had it completed and mounted on the lathe.

Materials include two 1 1/2 inch thick blocks (turned from scrap pieces), 1/2 inch dowel, and the 1/2 inch bushing that came with the buffing and grinding wheels. Note the 1/2 inch holes drilled in each block to receive the 1/2 dowel (arbor). The holes are 1 inch deep.

Dowel with bushing ready to insert through the buffing wheel.

Dowel inserted with bushing in the arbor hole of the wheel. Note the dowel length is cut 1/2 inch shorter than the combined 1 inch deep holes in the turning (compression) blocks, plus the thickness of the wheel.

Assembly is complete with turning blocks over the dowel and ready to mount on the lathe. When chucked up between centers on the lathe the buffing wheel will be in compression and will not slip between the blocks with the proper amount of pressure applied.

wood lathe part and Accessories

Unless a workpiece has a taper machined onto it which perfectly matches the internal taper in the spindle, or has threads which perfectly match the external threads on the spindle (two things which almost never happen), an accessory must be used to mount a workpiece to the spindle.

A workpiece may be bolted or screwed to a faceplate, a large flat disk that mounts to the spindle. Alternatively faceplate dogs may be used to secure the work to the faceplate.

A workpiece may be clamped in a three- or four-jaw chuck, which mounts directly to the spindle or mounted on a mandrel.

In precision work (and in some classes of repetition work), cylindrical workpieces are invariably held in a collet inserted into the spindle and secured either by a drawbar, or by a collet closing cap on the spindle. Suitable collets may also be used to mount square or hexagonal workpieces. In precision toolmaking work such collets are usually of the draw in variety, where, as the collet is tightened, the workpiece moves slightly back into the headstock, whereas for most repetition work the dead length variety is preferered as this ensures that the position of the workpiece does not move as the collet is tightened, so the workpiece can be set in the lathe to a fixed position and it will not move on tightening the collet.

A soft workpiece (wooden) may be pinched between centers by using a spur drive at the headstock, which bites into the wood and imparts torque to it.

A soft dead center is used in the headstock spindle as the work rotates with the centre. Because the centre is soft it can be trued in place before use. The included angle is 60 degrees. Traditionally a hard dead center is used together with suitable lubricant in the tailstock to support the workpiece. In modern practice the dead center is frequently replaced by a live center or (revolving center) as it turns freely with the workpiece usually on ball bearings, reducing the frictional heat, which is especially important at high RPM. When clear facing work that must be supported on both ends but cannot be accommodated with a steady rest, a half dead center, also known as a notch center, can be used. A lathe carrier or lathe dog may also be employed when turning between two centers.

In woodturning, one subtype of a live center is a cup center, which is a cone of metal surrounded by an annular ring of metal that decreases the chances of the workpiece splitting.

A circular metal plate with even spaced holes around the periphery, mounted to the spindle, is called an "index plate". It can be used to rotate the spindle a precise number of degrees, then lock it in place, facilitating repeated auxiliary operations done to the workpiece.

Modes of use

When a workpiece is fixed between the headstock and the tailstock, it is said to be "between centers". When a workpiece is supported at both ends, it is more stable, and more force may be applied to the workpiece, via tools, at a right angle to the axis of rotation, without fear that the workpiece may break loose.

When a workpiece is fixed only to the spindle at the headstock end, the work is said to be "face work". When a workpiece is supported in this manner, less force may be applied to the workpiece, via tools, at a right angle to the axis of rotation, lest the workpiece rip free. Thus, most work must be done axially, towards the headstock, or at right angles, but gently.

When a workpiece is mounted with a certain axis of rotation, worked, then remounted with a new axis of rotation, this is referred to as "eccentric turning" or "multi axis turning". The result is that various cross sections of the workpiece are rotationally symmetric, but the workpiece as a whole is not rotationally symmetric. This technique is used for camshafts, various types of chair legs.

[edit] Varieties

The smallest lathes are "jewelers lathes" or "watchmaker lathes", which are small enough that they may be held in one hand. The workpieces machined on a jeweler's lathes are metal, jeweler's lathes can be used with hand-held "graver" tools or with compound rests that attach to the lathe bed. Graver tools are generally supported by a T-rest, not fixed to a cross slide or compound rest. The work is usually held in a collet. Common spindle bore sizes are 6 mm, 8 mm and 10 mm. The term W/W refers to the Webster/Whitcomb collet and lathe, invented by the American Watch Tool Company of Waltham, Massachussetts. Most lathes commonly referred to as watchmakers lathes are of this design. In 1909, the American Watch Tool company introduced the Magnus type collet (a 10-mm body size collet) using a lathe of the same basic design, the Webster/Whitcomb Magnus. (F.W.Derbyshire, Inc. retains the trade names Webster/Whitcomb and Magnus and still produces these collets.) Two bed patterns are common: the WW (Webster Whitcomb) bed, a truncated triangular prism (found only on 8 and 10 mm watchmakers' lathes); and the continental D-style bar bed (used on both 6 mm and 8 mm lathes by firms such as Lorch and Star). Other bed designs have been used, such a triangular prism on some Boley 6.5 mm lathes, and a V-edged bed on IME's 8 mm lathes.

Smaller metalworking lathes that are larger than jewelers' lathes and can sit on a bench or table, but offer such features as tool holders and a screw-cutting gear train are called hobby lathes, and larger versions, "bench lathes". Even larger lathes offering similar features for producing or modifying individual parts are called "engine lathes". Lathes of these types do not have additional integral features for repetitive production, but rather are used for individual part production or modification as the primary role.

Lathes of this size that are designed for mass manufacture, but not offering the versatile screw-cutting capabilities of the engine or bench lathe, are referred to as "second operation" lathes.

Lathes with a very large spindle bore and a chuck on both ends of the spindle are called "oil field lathes".

Fully automatic mechanical lathes, employing cams and gear trains for controlled movement, are called screw machines.

Lathes that are controlled by a computer are CNC lathes.

Lathes with the spindle mounted in a vertical configuration, instead of horizontal configuration, are called vertical lathes or vertical boring machines. They are used where very large diameters must be turned, and the workpiece (comparatively) is not very long.

A lathe with a cylindrical tailstock that can rotate around a vertical axis, so as to present different tools towards the headstock (and the workpiece) are turret lathes.

A lathe equipped with indexing plates, profile cutters, spiral or helical guides, etc., so as to enable ornamental turning is an ornamental lathe.

Various combinations are possible: for example, a vertical lathe have CNC as well (such as a CNC VTL).

Lathes can be combined with other machine tools, such as a drill press or vertical milling machine. These are usually referred to as combination lathes.