You may ask why if the error was 0.001in. on diameter was the adjustment not only
0.0005 in.. The reason being because the change of angle will have an effect on the
smaller diameter also, this assuming the top slide is well extended and that both
flanges are in advance of the top slide's pivot axis.
If the error in the difference is larger than required, again leave the tip of the
tool in contact with the larger diameter having made the test cut, but this time,
after loosening the top slide, wind out the cross slide and then wind it back in
stopping 0.001in short of its previous reading. The top slide, then being rotated
so that the tool again touches the test piece, this setting it to a shallower angle.
Skim over the test piece once more and again measure, repeat the process until the
desired result is achieved. I can guarantee that the process is easier to carry out
than to describe.
I realise that the values I have quoted in the table are given to one tenth of one
thou and this is beyond the level of precision that will be available in the home
workshop. However, giving the values that precise will arm the user with the knowledge
that, for example, for number One Morse taper, just under 0.802 is preferable to
just over, if I had however rounded the value in the list to 0.802” then the user
would be unaware of this fact and may accept a slightly higher value. Do not expect
to arrive at precisely the value given but aim to get within half of one thou, that
should easily be achieved, which will still result in an adequate fit.
The difference value though is more critical so aim to be as precise as possible
though again absolute precision cannot be expected. With that accepted it is preferable
for the taper to be such that the angle is steeper so that the taper is tightest
at the larger end, for obvious reasons.
When used a second time the top slide can first be set to just touch each flange
but as the chuck may not be holding the test piece exactly as when used previously
it will still be necessary to skim the flanges and check the diameters. It will though
enable the slide to be set initially very close to required angle thereby reducing
the set up time appreciably.
Having set the top slide to the required angle the process now consists of straight
forward outside diameter turning. One aspect though of turning longer tapers is
that the travel of the top slide may be insufficient to finish the taper at one pass.
This will be no problem at the roughing stage but can cause a small step in the taper
when finishing off.
To minimise the effect use the following process. First, finish the smaller end leaving
the larger end unfinished over a length that the slide will cover at one pass. This
ensures that if there is a step it is furthest from the working end of the taper
though the following will virtually eliminate the possibility.