Polycarbonate edge finish SO3

HI all,
I’m preparing to cut a dust shoe out of Polycarbonate. I’ve been rehearsing LOL, started with mdf to check for design flaws then switched to test cuts on Poly. It doesn’t seem to matter a lot if I go from feed rate between 80 to 120 IPM with a speed of 1-2 or even 4-5 on the dewalt 611, DOC is .8 to .12, bit is #201 1/4" 3 flute from Carbide. my work is being secured with plenty of the thick 3m heavy duty tape. My edge finish is always the same, poor (in my opinion). here are 2 pictures.

What has been other peoples experience?? Is it my cutter? Will a better edge come with say a “0” flute up cut etc. etc.?
I’m using v-carve pro and my circles look good (not segmented).

P.S. I have tried leaving .010" allowance and doing a full depth finish pass with same results. Material is 1/2" polycarbonate.

Really appreciate all input thanx, Ray

Have you tried leaving the roughing clearance, putting in a new sharp (HSS if possible) bit and then taking the finishing pass in each direction to see which is better?


You should experiment w/ speeds — might want to add cooling.

Also, if the pieces were thinner you could try flame polishing — might want to try that anyway.

Did leave the roughing clearance with no change. Tried 7 different speeds, no change and you can’t flame polish polycarbonate with very good results. Are other people getting better initial results?

There’s a bit on the wiki if you haven’t seen that: http://www.shapeoko.com/wiki/index.php/Materials#Polycarbonate_.28Lexan.29 — this post was the most successful, but the pieces were quite a bit thinner: http://www.shapeoko.com/forum/viewtopic.php?f=7&t=8358&p=65150#p65150 — one link has the person using a Kress which can achieve a much lower RPM

Have you calculated the chip size you’re cutting for each speed you’ve tried? Varied the feed rate in concert to try to maintain chip size?

Hadn’t realized polycarbonate wouldn’t flame polish — my apologies.

No apologies needed. Chip sizes looks great, bit seems to be working well in that regard. Chips well, sounds descent, just seems the finish is not great. Maybe I’m expecting to much ?

Have you tried a Heatgun at High?

I almost want to ask for you to make a video of the cutting… you should be getting cleaner cuts… it’s almost as if something is loose causing the bit to vibrate hitting the edge inconsistently. Have you tried a two flute bit? maybe a 1/8"


After struggling for a long time with pretty surface finish, Jean is spot on with the heat gun idea. I was watching some custom car show and watching a guy on TV who builds plexiglass boxes for a living and he takes a small (harbor freight) torch and lightly puts it on the edges and they shine like the top and bottom surface. I will admit it takes a little practice, but now I could care less about what comes out of the machine.

That doesn’t work for polycarbonate.

You can “chemically polish” polycarbonate.



I get similar results using a 2 flute bit. I just picked up some single flute bits designed for plastic and see if they provide better results.

I was able to flame polish acrylic, but used MAP gas, not propane.

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I’ve run the machine for about a total of 30 mins. just getting to know it! I did go through yesterday and tighten things up (v-wheels) as they had loosened a lot, checked my belts and a fresh bit. Ran another circle and got marginally better results. HOWEVER, I did take some 320 grit paper and then 1000 grit and with a few passes of each was looking shiny new. I may grab a piece of regular acrylic to see if it produces any better results!

Thank you everyone for looking in and offering support, it is much appreciated. I’m still hoping others will look and maybe help with the problem or determine that it is as good as it gets with polycarbonate. Thanks Ray

Since it’s a simple cylinder, have you considered hand-coding a G-code file? That’d eliminate issues w/ the input as a possibility. Sample on the wiki: http://www.shapeoko.com/wiki/index.php/File:Circle-diamond-square-50-45-40mm.txt

Also, try G-Wizard and see what it suggests for feed-speed?

The other thing to do is to check in w/ a local endmill supplier — take some of the material which you have and some which you’ve cut and ask them for their suggestion on what endmill to use.


I have used the above “0” bits for poly and plexi. Very smooth finishes. I’ve used 0.125 & 0.25 bits with equally good results. Hope this helps.


Thank you Tom, I will give the them a shot. The carbide 3d bit will give me no better than what is pictured above. I still used it to cut out my dust shoe (pictures tomorrow). If I wanted to, it wouldn’t take long to sand out the edges and give a quick polish but would really like to find a bit that gives me a better initial finish. Thanks again Ray

I finished my dust shoe finally! I was never able to get a clean edge with my bit and have ordered a couple of the “o” bits.
Learned a lot about feeds and speeds while working with polycarbonate and cant wait to try the new bits. Thank you All, Ray