Suggestions for Bits to Use on Plastic

[buddym]

I am cutting some 3/16" plastic, I thinks its PVC or ABS... it seems kind of hard for PVC..... When cut with a 2 flute 1/16" end mill the bit ends up getting some buildup and then gets warm enough to melt/distort the work a little bit. I have read of up-spiral bits that do a better job of clearing the chips from the bit/work........ do you think this will help with issue, or am I going to need coolant? At this point my spindle speed and feed rate are pretty much fixed, so faster feeds or slower spindle speeds are not an easy option.

Thanks,
Buddy

[Fixittt]

different plastics require different speeds. most all of them have a low melting point. The idea is to have the spindle speed and feedrate set to where as the chip gets cut it pulls the heat away. Your spindle speed maybe to high and the rubbing of the flutes in introducing heat to the plastic. Eventually it will gum up and create even more problems. Very sharp cutters is also a must. I would highly recommend some type of coolant to help keep heat down to a minimum. I have machines all sorts of plastics and coolant was needed because my spindle motor didnt have enough torque to keep the rpms at a certain range. Due to your fixed spindle RPM you might want to play around with feedrates. go a little higher if you can, but coolant is the best remedy here.

[stevespo]

I have mainly cut Lexan, acrylics and HDPE, using 2 flute spiral upcut (1/4") bits. Melting/fusing has always been an issue, but it is definitely helpful to reduce the cutter RPM and increase the feedrate.

Recently I cut some Lexan with a 2 flute, straight cutter (1/4") and had better results than the spiral bits. 10,000 RPM (my minimum router speed) and 40-60 IPM produced decent results. I've been told that the single flute bits work even better for plastics, but have not tried them myself.

If you can run a little mist of water at the cutter, that would be great. I can't really do that because my work surface is MDF. Compressed air may help a little, but didn't do too much for me.

Good luck, let us know what works for you.

Steve

[edmond]

Try the "O" flute up spiral single flute cutters, these work like a charm.
Onsrud cutter have a wide variety of O flute cutters specifically designed for hard and soft plastics check them out at www.onsrud.com under the plastics cutter section.
We typically run these cutters at 18000 rpm on the cnc at work
I would second the idea of using a slight water mist, helps keep the cutter cool we do this at work on our Multicam CNC Router.

[Fixittt]

i tend to do things on a very small scale. I cut this in acrylic. Used some way lube as it cut to keep things cool and lubed. No melt back.
Rough in was a 1/16th ballnose 2 flute. Finish pass was a 15 degree .005 tapered 2 flute endmill. High RPMs, SLOW feedrate due to the model flexing.

This was a test cut for a minitech minimill 3 pro that I have been working on for a client.

[stevespo]

Edmond, thanks for the advice, I will look at those cutters. The only downside (for me) of running spiral upcut is that I tend to use heavy double-sided tape to hold down the plastic parts, and the upcut tends to lift them off the table. When I can screw then down, that works great. I do occasionally vacuum small parts down, but only for multiples with dedicated fixturing.

Fixitt, that is a great looking carving. You must have micro-meshed and buffed it clean?

Steve

[edmond]

We have a vacum table on the CNC at work but the upcut spiral O cutters can have a tendency to lift thin flexible materials. For cutting thin materials I would try using a straight O flut single flute cutters, I have tried using downcut spiral O cutters they work well pushing the material down but the finish is not that good due to the downward chip flow, sorry I didnt notice the material was so thin you were cutting.
Hope that helps

[Fixittt]

Steve,
the first picture is of the rough in with a 1/16th ballnose
the second pic is after the finish pass with a 15 degree tapered ballnose endmill tip .005 the finish on the finished piece is untouched. That is exactly how it came off of the machine.

[buddym]

thanks for all the advice, I ordered 1 of the single flute upcut bits from onsrud, the part number is 63-750. It's 1/16" with a 1/4" shank. Will let you know once I test it.

Buddy

[buddym]

Hi All,

The Onsrud bit worked great, cut the material like butter....until I snapped it after cutting one sheet of parts. I wasn't even running a cut, I was clear some stuck chips from it with the spindle and table paused!!! Man, I was SO dissapointed in myself. $24.50 plus $10 shipping..... gone after one great cut..... oh well, live and learn.... 1/16" is very easy to break... Does anyone know of similar bits that don't cost quite as much?


Buddy

[edmond]

Sorry to hear about that, I dont know of any cheaper O flute cutters though.
Try use a air nozzle directed at the cutter to help clear the chips while cutting, this really helps.just be ultra careful next time these small cutters break very easy