Machining Plastic (Centriboard) what bit to use?

[abelloise]

New at this...
Does anyone know what kind of bit, at what speed etc... is best to use when cutting a plastic board (ie centriboard).I have many parts that need to be cut on a regular basis.
Thanks!
Andre

[Geof]

Centriboard is recycled polypropylene with possibly some polyethylene as well. I would expect it to machine similar to polypropylene and HDPE or UHMW polyethylenes. These machine best with a very sharp cutter with good top rake and front clearance, a fairly high speed and a high feed so a healthy chip is formed and the cutter does not dwell in the cut. This way the heat from cutting is carried away by the chip.

Normally HSS tools can have a sharper cutting edge than carbides so the choice would be HSS. However because this material is recycled it would not be surprising to find abrasive material, otherwise known as dust and grit, embedded in it. For this reason it may be best to look into the high helix micrograin carbide tools used for aluminum. There are cutters for woodworking also that have a high helix and also single flute cutters are available, I think, and these provide more clearance for large chips from high feed rates.

As a starting point if the cutter is a 1/2" dia. two flute the speed could be 10,000 rpm, possibly even higher, and the feed maybe 0.02" per tooth. An air blast could be used for some cooling or a mister blowing just a mix of soap and water. (Watch out for rust if this is used.)

An important point is that it is probably flexible like HDPE or UHMW so it may need good clamping at many locations to preventing it lifting into the tool.