Cutting PVC - I want snow... all I get is sludge

CNC Machines Shapeoko
1

I find milling plastic’s the worst, I really struggle to make it snow and routinely get mixed results.

I’m using new, 1/8 single flute blades. Cutting 1mm DOC, at 1000mm a min, delay on 2.5.

Is it a case of I’m going too fast? I’m clearly melting the plastic but struggle to find a balance that works?

IMG_7413.jpg3024×4032 1.49 MB

2

By “delay on 2.5” do you mean a Dewalt at 2.5 dial setting?

Per Shapeoko CNC Router, Rigid, Accurate, Reliable, and Affordable that’d be ~18,000 RPM and in a 1/8" endmill, makes for a really fast surface speed (SFM) — 1 would be at least a little bit slower — might be enough.

Unfortunately, increasing the feed rate only helps so much since the machine can only accelerate so quickly — any possibility of a Makita? Its low-end ~10,000 RPM helps a lot for this sort of thing.

Please note that the official suggestion for PVC is:

DOC: 2.29 mm
RPM: 15820 (Dial setting: Dewalt: 1, Makita: 2.75)
Tool: 1/4" #201 square or #202 ball
Feed: 889 mm/min
Plunge: 432 mm/min

3

I am not an expert on the subject but this is what I have done with some success:

  • Lower the speed of the spindle to the lowest possible (this avoid plastic melting). I use 1 in my Dewalt
  • Use high feed rate (this also avoid melting). I know the recommendation is 889 mm/min but I have used 1,200 and higher
  • Hold the plastic piece very well. Not only at the edges. You should hold the whole piece with vacuum if available, double tape or the crazy glue trick to ensure a good holding
  • Eat a little bit per pass. I use 1 mm per pass
  • Make sure the bit is sharped
  • Use a single edge router bit

I hope this helps

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4

I would double DOC, feed rate and you should be fine.
https://youtu.be/jIU-ilbTdm0
Some of these cuts were done at 100 IPM, run it fast. G/L Ray

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5

Thanks guys, I think if I was going to slow the router down past 10,k I’d wire up a proper spindle - an idea I have been toying with. I have tried 10k, but it’s not much better.

Other than my spindle speed I’d say I’m being very conservative with my cuts on this material… Maybe I just give up on plastics again for a while…

6

You are being to conservative. Deeper and faster.

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7

Lets not forget you have a 2.2kw spindle?

I’m only cutting 3mm deep anyway

8

Being conservative in feed rates doesn’t help in plastics — endmill heats up the plastic w/ the results you’ve experienced.

Slow down the router, speed up the cut, if need be, to baby the cut, reduce the depth of cut.

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9

I posted a video a couple post above I was using my dewalt running at 100 Inches per minute with 1/4" bit and 70 Inches per minute with an 1/8" bit . 3 mm with an 1/8" bit should be no more than 2 passes.
On the other hand you could be right and just give up on plastics G/L Ray

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