On Thu, 27 Oct 2005 20:23:48 GMT, Jim Flanagan
wrote:

Hello..
I wanted to ask anyone if they have attempted to do this on their
lathe. I only have a metal lathe and want to cut a flat archimedes
spiral onto a 1/8" thick piece of lucite. The spiral, fairly coarse,
would be something on the order of 6 turns/inch. The diameter of the
plastic would be about 3.5".

In any case, I could use some pointers as to how and efficently
accomplish this. Thanks for any advice you may offer.

-jim
It sounds like you want to cut a spiral on the face of a disc. Others
have responded with methods for cutting the OD of the part which would
give you a helix. If you are needing to cut a spiral then a manual
lathe isn't the best way for this because they are set up for
threading parallel with the Z axis, not the X axis. I have cut scrolls
on CNC lathes, but the CNC doesn't care which axis is being geared to
the spindle because it's all done electronically. If your lathe X axis
advances .200 for each revolution of the handle then you would need to
figure out some way to turn the handle 1.666666 revs for each rev of
the spindle. I can think of lots of ways to directly gear the
crosslide (X axis) to the spindle but they all would take a long time
to do. But if you can cut the groove in one pass I have an idea.
Remove the handle from the X axis and tighten the chuck on a drill
motor onto the shaft that the handle mounts on. With the drill motor
spinning at top speed see how long it takes the X axis to traverse the
required distance. Set the spindle speed on your lathe to the rpm that
will give you the pitch you want. Set the tool for the desired depth
of cut but have the tool pretty far in the X plus direction to give
the drill motor time to come up to speed. Start the lathe and then
pull the trigger on the drill motor. Crude, but it may work.
ERS