Harold Hall


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.


Workshop Projects

Cross Drilling Jig, making