Machining Acrylic

      Bit selection, feed rates, and other advice for cutting acrylic on a CNC router. March 1, 2006

We have some acrylic signage to do on 6mm sheet. We are using a 90 degree conic bit that we use for our mdf cuts normally.What should the speed and feeds be for acrylic? At the present time the cuts are very rough on the inside edge, and we canít seem to get a smooth cut edge using a spindle speed 8000rpm over all feed rates. Please advise if you can.

Forum Responses
(CNC Forum)
From contributor A:
If you can get a proper O flute acrylic bit, that will work best. Conventional cutting at 150-180 IPM, 18000 RPM, and 1/4" diameter bit works for me. If not, I used to use two flute carbide end mills at lower feed rates and, while it melts more, if you have the time to do a finish pass at full depth (taking about .020" off maybe), it should turn out OK. By the way, this is for extruded acrylic, but cast usually cuts nicer anyway.

From contributor B:
Solid carbide or carbide tipped tools are a must. For a .236" acrylic sheet you can use a 1/4" diameter bit but 3/8" or 1/2" would be better. We run feed rates at about 250 IPM and 18000 RPM. You can run faster or slower than this but this gives us the best cut. Another thing worth mentioning is that if you've cut wood with this bit since the last sharpening, the edge quality of acrylic will be crappy. You must use a cutter that has not touched wood. My favorite is an Onsrud 52-638 for a high quality edge.

From contributor C:
How large are the parts you are cutting from this sheet of 6mm? Make sure that the sheet is not shaking - stop the vibration and you will improve the finished edge.

From contributor D:
One more tip - don't use any cutter that has already been used on MDF or timber. You'll get better results with either a brand new cutter, or at least one that has been resharpened

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