"John" wrote in message
...
One word of warning on these centres and it relates to the angle of the
tip. Too Pointy

I had an issue with these when I started pen turning. You wind the tip
into the hole in the end of the mandrel and away you go , for a week or
two, then your stuck.

In some cases the hole in the end of the mandrel is not deep enough or
not wide enough, causing the tip to bottom out, and allowing movement of
the mandrel from side to side ( though not immediately visible). At
first it may not be noticeable but after a while you will find a groove
on the pin, and its all down hill from there. Next time your turning,
your work slips so you assume the problem is caused by the knurled nut
that clamps the tubes in place not being tight enough, so you nip it up
a bit and continue turning, then again its loose so you do it again.

What has been happening is that the bar of the mandrel is being pulled
out of the Morse Taper as the pin in the revolving centre wears (they
are normally are a press fit, though some recent designs are adjustable
so no problems) You will get to a point where it will not come out more
as you get to the width of the hole which matches the revolving centre
pin, but by then the damage is done.

If you can the best solution is a 90 degree revolving centre, and if
you can make a nut which will extend past the end of the mandrel and
provide a good mating surface to the revolving centre.


The end of a pen turning mandrel is drilled with a standard center drill for
use with a 60 degree center in your lathe.