Re: Engraving and engine turning

David,

I have done a bit of thinking on this subject (depth of cut when engraving
that is). I have a New Hermes pantograph that has a rub collar on the
bottom of the spindle. This "nose" is polished so that it won't mar the
work piece. You can set your depth by zeroing the cutter, then advancing
the nose up a few thousandths. Even though it's smooth, I don't like it
because metal shavings can get under it and scratch the piece. This is bad
when the piece is buffed and ready to send to the plating shop. What I
do now, (on my CNC mill) for engraving brass is to use a diamond drag
approach- dragging a cutter that has a diamond tip through the work piece.
This type of cutter can be bought from engraving supply houses and MSC for
that matter. It has a 120 degree angle on the end of it that prevents the
diamond from going in too far. My axis drive for Z also has a bit of play
in it- about 0.005" backlash, which I don't mind, because gravity takes
care of it- which for my setup is fine. So, I'm dragging the diamond
around on brass plate that I have just buffed, and the plate is stuck down
to the fixture with double stick carpet tape. If there is a slight low
spot in the brass where I have sanded it with 400 grit and buffed it hard,
the diamond seems to ride through the material consistantly. I used to use
rotary cutting tools- but never again on this project.

For your application- you could set up a servo or stepper to rotate the
spindle in the direction of cut, I'm not sure how you would set up the code
generator for this. On the depth of cut, you might use a follower nose, or
something similar. It would be nice to be able to use a pressure
transducer to tell the controller when to move the spindle up and down-
without the use of a follower. If you were using a rotary cutter, like a
normal V bit, maybe in theory the controller could read the current draw on
the motor and move up and down. My dream solution would be to digitize the
surface and run the tool path accordinly.
How wavy are the clock faces?

Dan Falck