Workshop Wednesdays - Deep-throat Step Jaw Chuck archive

Wednesday 12 February 2014

Gabor Lacko creates a deep-throat step jaw chuck which allows you to hold items of different diameters

Gallery

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


Tegan Foley

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Gabor Lacko , Workshop Wednesdays , Deep-throat Step Jaw Chuck

Background Of The Deep-throat Step Jaw Chuck

The original design was a purpose made jig - to deal with the chess pieces and nothing else. The variation between the smallest and largest base diameter was a little over 12mm, which corresponded to about 6mm of jaw movement. The result was four segments cut from a 75mm diameter cylinder, mounted on jaw plates, about 100mm high with one single 25mm diameter hole bored in the middle and concentrically with this one receptacle to grip the base of the chess pieces.
The movement of the chuck was sufficient to cope with the small variation of base sizes.
It was only years later that I made a 200mm diameter step jaw, with an entirely different purpose: reverse mounting of small cove and bead bowls. It was again quite a while before the two designs were brought together in the deep- throat step jaw chuck

Handy Hints

1. You might find it easier to drill the holes for the coach bolts before sticking the discs together, in which case, after drilling one set of holes you can use this disc as a template for the next one. This will save you a lot of time and extra effort and will ensure you get them right
2. The coach bolts used in this project have a small square section about 5mm long, just below the head of the bolt. Do not make a hole big enough to take the squares. If they pull into the round holes they will lock in and it will then be easier to tighten and loosen the nuts
3. If you like the concept of Nylon jaws – because they mark the timber less – substitute the top 24mm thick plywood disc with four discs cut from 6mm natural Nylon. Each step will be the thickness of the sheet material
4. You can customise your chuck by making it deeper or the throat can be of larger diameter. If you change anything, always consider the safety aspects


Diagrams Click an image to enlarge