On 16 Apr 2006 06:41:10 -0700, "Andrew VK3BFA"
wrote:

I want to turn up a round perspex piece to fit in a circular hole in
the front panel of a radio I am building. I start with a piece of
perspex 4 inches square, and turn in down to the required fit.

Had one go at it today - interesting. Generates enormous amounts of
swarf - ok, can live with that. Started by using a pointed tool to cut
it to roughly the right diameter - when it broke right through the
piece, it went "whang" and threw a big chunk across the room.
Mmm....not good.

Whats the proper way of doing this without generating missiles of
plastic (or steel, come to think of it.) - what sort of cutting tool
should I be using, and what speed should the lathe be running at, ie
fast or slow (yes, very technical..) Any lubrication required - it was
cool to the touch.

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?

Andrew VK3BFA.

I had to make a hole in my replacement aircraft windscreen for the
fuel filler which was an inch off the side. it was easy in the end.

I would drill the centre hole undersize you you can clean it up after
the process.
use a 1/2" by 1" length of wood just a little longer than the radius.
drill a hole in one end and reverse the drill bit to use the drill
stub as a pivot pin.
cut a slot at the other end to take your favourite perspex lathe bit.
I used a piece of 1/8th square tool steel sharpened at one end.
put a bolt through the end to clamp up the slot and hold the tool.

put the drill stub into the hole into the perspex and pull the tool
around by hand. adjust the angle of cut so that it cuts well. some
negative rake on the tool bit works well. cut in half way.
reverse the perspex and cut in the other half. when you have cut
through and pushed out the centre clean up the last little dags with a
fine file. then drill the centre hole to final size.

when I did my fuel hole in the windscreen it was with some
trepidation. turned out to be really easy and took 5 minutes.
half the trick is to do it by hand so that there is no heat buildup in
the cutting area.

Stealth Pilot