Cutting Techniques for PVC Board

A fabricating shop has problems working with expanded PVC foam board. Colleagues share advice on cutter choice, feed rate, and more. July 11, 2005

Does anyone have experience cutting Sintra on their CNC router? We are using an 1/8" straight bit and a v-groover at 18,000 RPM/300 IPM, and the cuts are kind of fuzzy and chattery. We are cutting well face down, but the up-cutting bit seems to pull the material off the table. Any suggestions would be appreciated.

Forum Responses
(CNC Forum)
From contributor F:
I have used 3/16" up and down geometries with an O flute design with success.

From contributor A:
O-flute is good choice if the rpms are too fast and/or the feed rate is to slow.

From contributor P:
What kind of machine and what spindle are you using?

From contributor S:
I've used a 1/4" down shear with rough and finish passes leaving a skin. Ive been able to cut at 800 in/min with good edge quality. An O flute is a good choice also.

From contributor G:
We cut Sintra day in and day out. When its done right, it cuts like butter. The diameter cutter that you are using should be fine, but if you could go to a bigger one, it would be better. 1/4" diameter at 550 inches per minute should be good. Solid carbide cutters or carbide tipped on plastic is needed.

The cutters that you are using shouldn't touch wood. Even cutting your spoil board with the production cutters should be avoided. The dullness of your cutters could be causing the fuzziness and also could account for your parts being lifted from the vacuum table.

Vibration by lack of vacuum could also be the culprit of chattered edges. I should also ask what thickness material are you cutting? The info above will work for materials 6 mm (1/4") or less. Thicker material should warrant larger cutter diameters.

From the original questioner:
The Sintra we are cutting is 1/4" thick. We are using brand new cutters, the 1/8" because we want a sharp inside corner, and were using the v-groover because we are folding the stuff into boxes. I'll try picking up the speed - should that help? Surprisingly, the vacuum doesn't seem to hold this stuff very well, and we are putting screws in the corners. Also, what is an O flute?

From contributor S:
The O flute is just one flute, producing rapid chip removal. It works very well on acrylics also. Instead of screwing it down, spray a little contact adhesive on the corners, or use masking tape to tape the edges down. I thought it was pretty funny until I tried it. It ran the miter folding bit slow without any chatter.