Philip Greenwood looks at methods of re-chucking.
In this part we look at a few methods to re-chuck the base of a finished item, or to hold an item. The cost can be very little, as most items to make the jigs will be in your workshop. Yes, a few do require you to buy additional chuck jaws to fit to your chuck, or other small items. One method I have not described here is a vacuum chuck; this is because I do not have one, but I know how useful one can be.
The most important part of whatever method you use, is that it is safe to use and will not leave marks on your finished work, or you have wasted your time. Some of the methods below do require you to hand finish to remove a small pip in the middle of the base, but this is easily achieved.
The jam chuck as it is called has been around for a very long time and is a very useful way to finish the base of items, or to hold an item for turning. To use one of these you need to mount a scrap piece of timber in your chuck, or on a faceplate that is larger than the rim of the item you wish to re-turn the base of, you can turn a spigot or recess in the scrap timber to hold on the inside or outside of the bowl rim depending on the rim shape. The most important process of using one of these is to achieve a tight fit, or as you try to use a tool on the item it will come out of the jam chuck. I use a tailstock for additional support for as long as possible. If when you try the fit it is very loose, the jam chuck will need to be resized. If it is a minor error, we have ways round the problem of a loose fit. The first method, if no finish has been applied to your item is to use a little water to swell the fibres of the timber, if you have already placed a finish on your item the finish can be damaged by the water, this is a limited time solution, for as the fibres dry out the item will become loose. A second way is to use paper towel to take up the slack. But this is no substitute for a good fit.
This type of chuck is useful for re-turning of bowl bases. This item is an adjustable gripping chuck, which can be made with timber we have laying around in the workshop, along with a few tools and a router. A friend of mine, Walter Hall, made one for the magazine a while ago.
To use this it is held in the lathe chuck and the Longworth chuck is rotated to the approximate
size of the bowl you wish to fit. Place the bowl on the face of the chuck and bring up the tailstock, and line the revolving centre up with a dimple you made in the spigot of the base when you first turned the bowl. Now adjust the chuck until the jaw’s buttons grip the bowl tightly. Now tighten the chuck nuts and bolts to hold everything in place. Reshape the base and remove the tailstock only for the small pip in the centre and then sand to a finish.
Jaws, wood plate
Some manufacture’s of chucks make plates to fit your chuck, to which you can screw a disc of plywood which is cut into four segments. Then you can turn grooves into this face and use it like a very large set of jaws, enabling you to contract and expand onto a bowl rim. This is like an adjustable jam chuck. Yes, you could make jaws for jobs that other commercial jaws would not hold or could damage the item. This enables you to completely finish the base as well.
Anti-slip matting on a disc
Some of you will have seen me use this method in the magazine and while out demonstrating. This consists of a piece of timber and some anti-slip matting. I use two types, one in a flat piece of timber with a recess on the back to hold on the chuck, the matting is glued on to the disc. This type is used on flat topped items only. The second type is a domed piece of timber, again with the matting glued on; this one can be used on a bowl with a natural top edge. You may need to make a few for different sized bowls. I always place a small dimple on the spigot or in the recess of the turned item to allow me to line up with the tailstock. These types are always used with the tailstock, you just need to remove the small pip afterwards and sand this small area, as most of the bowl can be sanded while on the lathe.