v carving and routing incised letters in plastic sheets

[Rocco.G]

Hi all

i've been playing around with doing some v-carving in left over plexiglass that i have around the shop. I do a lot of electrical signs and often have cut-offs that never seem to get used up. I'm considering making some "business cards" out of leftover 3/16" white plexiglass. As a test i got clipart of a ship and then put lettering above and below it. I kept the lettering as a bold gothic font since it was small.

i did a test cut and after playing around a bit, one run came out great. then I ran another a few minutes later and the bit started to melt the plastic chips which stuck to the bit and ruined the cuts. The bit ( a 1/32" ball nose in this case) was so hot that it burnt my thumb when i took it out of the spindle motor to clean off the stuck on plastic.

A small v bit worked well enough but it doesn't give the look I'm after for small lettering (say 0.3" tall) set into the plexiglass. Do I need to cut the feed rate waaaay down or are there better bits just for plastics? Maybe a small end mill instead of the ballnose? Or even an aluminum cutting bit perhaps? I don't have small enough endmills but can get some if that's better. Anyone have specific suggestions?

i also tried the same design in serveral differet types of wood (pine, poplar and maple, plus plywood). In larger sizes (about 8" x 10") it all looked fine but when i got down to the small letters, the edges were always fuzzy. Anyone have suggestiosn for small lettering in wood as well. Again the text is as small as .3". i can go bigger but don't want it to be larger than a cell phone. I'm figuring that most business cards are tossed but soemthing that's cool looking might be kept, even if many people are going electronic for business cards.

I can post the file (assuming that's allowed) if that would be helpful.

Thanks!

[coryatjohn]

Melting plastic typically indicates the speeds are too slow and the RPM's are too high. Lower the RPM's to the minimum and increase the speed. The problem with small bits and plastic is the chips, which carry away the heat, aren't ejected efficiently. That leads to melting.

[Rocco.G]

Ah, just the opposite of what I would have done. i'll give it a try.

Thanks!!!