Turning the casting through 90 Degrees and holding it on the two machined faces one
of the two remaining long faces will be against the chuck body. Having a taper, and
being much wider than the depth of the jaws, this can take over the positioning of
the casting, see Sk. 2. Use a square off the chucks face to check that this has not
happened. Machine the third side and then similarly the fourth.
Now having four machined surfaces for the chuck to grip, the ends can be machined
as in Photograph 3. With the degree of uncertainty regarding the positioning of the
part in the chuck so far it is unlikely all corners will be sufficiently close to
90 degrees, I hesitate to use the word, exactly. Therefore, skim over all six faces
once more using the following sequence, do still use the copper pads under the jaws
both to protect the machined faces and to increase the gripped area.
Set up the part in the chuck, again as in photograph 2 and give the top a finishing
cut. This time rotate the casting by 90 degrees and again tighten chuck and give
this second face a finishing cut. However, do not rely on the machined surfaces automatically
positioning the casting, but check with a square that the face just machined is square
to the chucks face. Repeat the process for faces three and four after which check
that the desired result has been achieved, that is, all four corners 90 degrees.
Now again set up the casting as in photograph 3 and skim the end. This time it will
be necessary to check two adjacent faces against the chuck with a square, Repeat
for the other end and you have the six faces finally machined. The overall dimensions
are quite unimportant so do not spend time attempting to arrive at a particular dimension.
In any case the drawings quote these dimensions as nominal.
Mark out the position for the jig fixing hole and centre punch. Set up casting, again
as in photograph 2 and set the centre punch mark to run nominally true, checking
it against the tailstock centre will suffice, though you could use a centre finder
if you possess one. This will though result in a very out of balance set up so now
wind back the one jaw and insert a substantial block of steel to improve the situation,
do ensure that the chuck is very firmly tightened again, we do not want this to fly
out when the lathe is up to speed. It will in any case be necessary to run the lathe
at a quite low speed as even a near perfect balance is unlikely to be achieved. Drill
to suit the diameter of the tool post on the lathe on which it is to be used.
Mark out, drill and tap the three 1/4" BSF holes.