Hexagonal auxiliary jaws
As it becomes necessary to machine the jaws for different diameters and depths, eventually
the jaw will become so reduced in size that it will be impracticable to machine them
further. This can largely be overcome by using auxiliary jaws mounted on top of the
standard soft jaws.
One example of this is to add hexagonal auxiliary jaws as shown in Sk. 2. These can
be rotated so that each corner can be used for a different diameter. Provided that
the hexagons are appreciably larger than the width of the chuck jaw then the resulting
machined portion should provide as much wrap around as the plain jaw, Sk. 3. Where
a greater width of grip is required, particularly required at larger diameters, then
three jaws as illustrated in Sk. 4 can be used. This method is extensively used by
wood turners using nylon add on jaws.
Having made and used the jaws for the first application mark them with the diameter
they are intended to grip and the jaw number on which each one fits. Soft jaws must
be fitted in the correct position in the chuck in the same way as normal jaws and
the auxiliary jaws must also be paired with the jaw onto which it fits. When reusing,
fit the three auxiliary jaws leaving the central screw such that the jaw can just
be turned. Place the workpiece into the jaws and very lightly tighten the chuck thereby
aligning the jaws correctly. The central screws can now be tightened fully and the
chuck also tightened to enable machining of the workpiece to take place.
Making Hexagon Jaws
Sk. 5, showing my suggested design for shop made jaws, shows that each jaw has a
boss that locates into a counter bore in the soft jaw itself. It is essential that
this is a close fit in the jaw otherwise there will be no guarantee that the hexagon
jaw will return to the same place when it is removed and subsequently returned. The
size of the boss is not important but would suggest 4mm deep and a diameter of between
1/2 to 3/4 the width of the jaw.
Making the hexagon jaws is straight forward other than to say the bosses on each
one must be exactly the same diameter. Concentricity with the outer hexagon shape
is worth aiming for but is not crucial as any error will be eliminated when the jaws
are eventually machined to the required diameter. Whilst geared up for making these
jaws, making a second set would be a wise move. Of course, whilst the hexagonal jaws
are shop made the main soft jaws can still be those available commercially.