As commented on on the first page the design was established with a wish to limit
the need for precision. Whilst this has been largely achieved there is a need for
repeatability between parts making the choice of the manufacturing method used an
important one. This is mainly to ensure that the clamping method is capable of securely
holding each holder to the base. The cam action of the locking spindle does of course
provide some room to cope with minor differences.
The semicircular grove (B) in the holder was produced by clamping two holders back
to back and drilling down through the join. I did this with just a drilled hole but
later felt that reaming this prior to separating the parts would have been worthwhile
and would suggest this is dome. Even with this done it is inevitable that there will
be minor differences in the depth of the grove between the two parts and other holders
and subsequent operations have been chosen to cope with these differences.
Having made the Body (1) and fitted to it one Locating Key (6) and one Spacer (7)
this can then be used as a jig for positioning each holder in turn to mark out the
position of hole (C)
Mount the body onto the milling machine table using the central hole and a fixing
stud, then mounting the first holder onto this, clamping it with a toolmakers clamp
of similar. With a centre drill in the machine spindle use the X and Y table movements
to establish the position for the hole to be drilled ensuring the table clamps are
set. With that done, mark out the position of the hole in the first holder using
the centre drill. Then fit and mark out each additional holder in turn ensuring that
the tables are not moved during this process. Adopting this method will compensate
for any variation between holders in the depth of the grove. A 10mm drill can now
be placed in the machine spindle and each holder returned for final drilling, again
without moving the tables.
The Body can also be used as a drilling jig for drilling the 8mm hole in the Operating
Piece (31). Packing, having a suitable thickness, is placed between each flat on
the Clamp Piece (32) and the Body and the whole assembly clamped to permit drilling
to take place. Do ensure that the Clamp Piece is upright before clamping for drilling.
Note the comments in Sk. 2 regarding the position of the hole when choosing the thickness
of the packing pieces.