Clean Grooves in Acrylic

      Advice on machining V grooves into acrylic without re-welding problems. October 28, 2008

Question
We have been offered a job cutting what could be several hundred sheets of 3/16" acrylic. Each 4x8 sheet needs to have a brick pattern cut with a 60 degree v-groove bit. Has anyone tried to profile cut acrylic? We are having issues with re-welding in the v-groove. At the present time, we are running at 225 ipm, and have tried anywhere from 9000 to 18000 rpm, cutting at least twice (some need three passes to clean the groove). Any way I can cut this groove in one pass?

Forum Responses
(CNC Forum)
From contributor W:
We did this often at the sign shop I used to work for. I used an air blower pointed at the bit and never had a re-welding problem. I think it was about 200-250ipm at 18000rpm. I guess the biggest thing for you might be the grade of acrylic they want. We always used cast acrylic (GP) which machines much better than the continuous cast stuff (FF). The FF is cheaper but it doesn't machine as well.



From contributor N:
Also consider using a sign making or engraving bit. A regular v bit goes to a point. There is no cutting speed at the tip of the bit, so it basically burns through the material. An engraving bit has a small flat and a bigger area to evacuate the chips so they won't re-weld.


From contributor M:
Just did some of this a few weeks ago, inscribing circles in acrylic sheet. I wish I had retained the feed and speeds, but I know I used a single flute miterfolding bit, replaceable tip, and had severe re-welding on the first try. Put a fresh sharp knife in, adjusted speeds (again, sorry I don't remember what they were) and used a second very shallow cleaning pass. Results were very good, so it can be done.


From contributor C:
Consider installing a Vortec cold air gun at the spindle nose to chill the acrylic and also blow the chips from the cutting path.


From the original questioner:
Thanks for the advice. I had a talk with my client and we decided to run slower (150 IMP 17000 RPM) and run twice. Client agreed to pay a little extra for a piece he doesn't need to touch.

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