Cutting Expanded PVC Sheet Goods on a CNC Router

Advice on bit choice, feed speeds, RPMs, and related issues when machining expanded PVC plastic sheet material on a CNC router. August 5, 2010

Question
I am looking for some feedback on feed rates and tool recommendations for Expanded PVC or Sintra for a job I'm bidding. The part has some pocketing, and regular perimeter cuts through the material. It's 1/4" thick. It looks like I will be using a 1/4" tool, and a 1 1/4" fly cutter. Any info would be appreciated.

Forum Responses
(CNC Forum)
From contributor T:
I work for a plastics company and we cut expanded PVC on a daily basis. It's about the easiest plastic to cut. It doesn't throw a chip, it pulverizes. In general you can cut 150 to 200 ipm at 18000 rpm. You will be amazed at how easy and forgiving it is to work with.



From contributor G:
Are you using a single o-flute? At a 1/8" diameter I was finding significant melt back, and had to drop my rpm's back to 10,000 rpm, with a mere 45 ipm in order to avoid pulling the sheet up (spray adhesive and 10hp vacuum table). I was cutting 5" lettering from a 1/8" sheet, resulting in never reaching full acceleration. I'd love to cut this stuff faster - is the small bit diameter a big factor?


From contributor T:
Yes, the 1/8" diameter can be a problem and you will not get to 200 ipm. We try to go 1/4" to 1/2" diameters when we can. We do a lot of letters and logos. Itís not uncommon for us to be cutting 1/2" Sintra. In those situations we will do a rough cut with a 1/4" bit about .015 over the finished size and come back with an 1/8" to finish it. O-flutes work better on the smaller diameters, but normal straight 2 flute wood bits work fine over 1/4". What is really important is to use a brand new bit. Even just a couple cuts in wood will kill it for plastic. Also try to avoid plunging straight into the material, use a ramped entrance.


From contributor G:
I do ramp into all materials - what ipm on the finishing 1/64th pass with the 1/8" bit?


From contributor T:
It's dependant on the material thickness, but at 1/8" you should be able to run in the 80 ipm range with no problem.