Three things are of importance when setting up a workpiece for machining on the rotary
table. 1. The position of the workpiece on the table. 2. The position of the table
in relation to the machine spindle. 3. And finally, the position of the cutter relative
to the workpiece.
Without doubt, number one is the most critical as if incorrect no amount of adjustment
of the milling machine table will compensate for this. What then are the requirements?
In all cases the required position of the workpiece will be relative to the rotary
table's centre. Unfortunately, herein lies what at first would appear to be a difficult
problem as all rotary tables have a substantial hole in their centre and the user
is therefore attempting to determine a point to measure from that exists in fresh
air. This though is not as difficult as may first appear, certainly not in the case
of the shop made tables that have a parallel bore in the centre of the table. The
commercial tables do though have a Morse taper in the centre of the table that for
me places an added complication. I will though first give my suggestions in relation
to the parallel bore and later add my comments as to how this can be overcome in
the case of a table having a Morse taper.
Let us then discuss two simple applications. First, a very frequent requirement,
adding a radius to each end of a link as shown in Sk 1. This would appear to be
a very simple task but unless the end of the link is placed exactly on the centre
of the rotary table then that shown in Sk. 2 will result. In this case, no amount
of adjustment to the X and Y axis of the machine will correct it.
How then do we get the hole in the link exactly on centre, the answer is to use a
locating spigot as shown in Photograph 5. This is made a close fit in the tables
bore and with a short extension that is a close fit within the hole on the end of
the link being radiused. For this to work though the pre drilled hole must also be
central in the link else the result will again be as Sk. 2. Photograph 6 shows an
extreme example where a deep radius is being made on a narrow and very short workpiece,
(part seen on the table in photograph 5). Locating such a workpiece by any other
means would be quite difficult.
Sketch 3 shows a rather more complex requirement, placing a radius on the ends of
a crank arm and along its length. Photograph 7 shows the second end being radiused,
much like that in photograph 6 except that it is being made over an angle greater
than 90°. The result of machining the first end can be seen on the right of the photograph.
This is an example of a process where end stops would be very useful.