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Workshop Wednesdays – Deep-throat Step Jaw Chuck


Monday 9 July 2018

Step jaws, as the name implies, have several steps to accommodate different diameters. This chuck is very similar to the above design but it is much deeper with a 25mm diameter hole in the centre. It is based on a chuck I first made about 20 years ago for a woodturner who received an order in October for 24 chess sets to be ready for the Christmas market. That meant him making about one chess set a day, and he needed a quick method to tidy up the 768 bases.

Since then I have modified the design and now it not only accommodates one certain base size – with small variations between the king and the pawns – but with three or more steps it can also be used for finials and goblets, and for small bowls, both inside and outside.

STEP 1

You will need 24mm plywood for making this deep-throat step jaw chuck. Cut three discs to 160mm diameter. The plywood stack will be mounted on a 150mm 'wood-jaw' plate

STEP 2

The segments form a perfect circle when 0.1in open, because they were turned circular and use a 0.1in slitting saw to separate them. On one of the ply discs mark out the screw hole centres, using the plate mounted in the chuck as a template. The chuck, with plates mounted, has to be 0.1in open. You need to draw in four lines – two pairs 0.1in apart – which will divide the disc into four quarters

STEP 3

Stick the three discs together, and then drill the eight holes…

STEP 4

…and cut it into four segments

STEP 5

Mount the wooden segments on the wood-jaw plate. Use 6mm coach bolts, 100mm long. I know that it is tempting to use woodscrews but nuts and bolts – and lock washers – right through the assembly cannot be beaten when safety is considered. Spring washers and Nylock nuts will give a secure fixing. Now tighten the nuts

STEP 6

When all is well, turn the outside of the stack – 0.1in open – to a circle to get rid of the saw marks, sand it, and turn four steps each about 0.5in wide and about 6mm deep. Bore or turn out the centre as big as the smallest step allows it

STEP 7

This diameter will decide the maximum diameter of finial, chess piece, bud vase, work etc. which can be mounted…

STEP 8

…on the chuck, or in it (as shown opposite)

STEP 9

The completed chuck with a turned chess piece