D Murphy wrote:

"Andrew VK3BFA" wrote in
oups.com:


Its got a quarter inch hole in the middle to allow the vernier drive
shaft to pass through to the tuning knob - I cut the head off a bolt
and used this to chuck it to the lathe. Its got a bit of wobble,
probably need to get a straighter bolt - was grabbed out of the junk
box.. Is there a better way of mounting the project?

Words of competence?


As others have said, I would sandwich the acrylic (perspex) between some
wood or aluminum or what have you. That will help with break out at the end
of the cut.

Acrylic has a very high thermal coefficient of expansion. It's better than
six times that of steel and three time that of aluminum. It's also a poor
conductor of heat. To get the best results you need a sharp tool, high
speed and low feed rates. For a HSS tool you should run around 400 SFM and
.001-.005" IPR feed rate.

The tool should have zero top rake and zero back rake. Positive rake tools
will only increase the chipping problem and will try to make the work and
tool suck into each other. However, the tool needs massive amounts of end
and side relief to to the thermal expansion. Around 30 degrees end relief
and around 20 degrees side relief. Hone the cutting edge so that it's very
sharp. Lighter depth of cuts are better than deep cuts. I would take no
more than .04" per pass.

I've heard of guys rigging up shop air (a gentle stream) to help with cooling
when turning plastics.

GWE