Next place a length of 10mm diameter in the three jaw, or collet, with about 50mm
projecting, and very lightly centre drill the end with a small centre drill, support
the end and turn to 3.95mm diameter by 38mm long Photograph 3. Create the knurl on
the head, part off, remove, rotate and return and face the end of the head to length.
Finally, reduce the length to 35mm to remove the drilled centre, if you cannot get
the head behind the jaws of your chuck, or a suitable collet, then reduce the length
by milling as being a measuring device a flat end is essential.
Ideally, the length of this should be such that when fully depressed the holes in
the base and clamp align perfectly. This enabling the spindle to move freely though
both. If too long then the spindle will not be able to enter and if too short the
pressure applied by the user will tend to clamp the spindle in place. Whilst worth
aiming for this is just a nicety and not essential. However, the following is the
method to attempt to achieve this.
I would suggest a suitable spring would be in the order of 8mm diameter and wound
with a wire in the order of 0.9mm diameter though these values are far from critical,
it does though need to be a rather strong spring. With that size spring in mind
cut four complete turns and lightly grind both ends flat. Do not try to hold the
spring in ones fingers or even a pair of pliers but use the following method which
is perfectly safe.
Chose a drill whose shank is just too large to enter the spring freely but with a
screwing action that will lightly unwind the spring the shank will enter the spring
which will be firmly held, the spring can then be applied to the grinding wheel perfectly
safely. To remove, hold the outer turn with a pair of long nose pliers and with an
unwinding action the spring will be removed easily. Keep repeating the action until
the spindle just passes through when the spring is fully compressed. If you do not
have a suitable size drill then turn a length of steel to do the job.
Normally the large gauge would be used but the smaller will be useful where space
is very limited, Photograph 4 shows one assembled and the smaller dismantled.