Machining Acrylic on the CNC

Advice on the fine points of cutting acrylic. February 12, 2010

Question
What spindle speed and feed rate is the best for 1/4" Acrylic using a 1/4" O flute? Any input is appreciated.

Question
(CNC Forum)
From contributor G:
Well, I believe it depends on the rigidity of the machine and hold down, HP of router and how it is programmed, but we use about 150ipm for what it is worth with a spiral Onsrud 1/4" bit. I am sure that we could go faster, an sometimes we do, but that speed gives a reasonable finish without a finish pass and with our aluminum (CNT) machine and Regen blower vacuum setup. We are shop doing lots of small jobs, so slow and steady wins the race. Production jobs get the tweaking.



From contributor G:
Sorry: 16-18K rpm on an HSD spindle.


From contributor P:
Try using a Misenhemer 570-0540 - they work great.


From contributor K:
One other thing you need to worry about when machining acrylic is what type it is. Is it cast or extruded? Is it FF, SG, MC, or etc? This does make a difference. Some acrylics you need to climb mill and others you need conventional mill. My suggestion is to use a 1/4" O flute with finishers, rpm 15,000-18,000, feed rate around 150-200 ipm. Thatís how I cut acrylic. Keep in mind this is just a starting point for you. Every machine is different as well as every machine handles tooling different. Also try using an air blower. You donít want to keep the chips in the groove. Hope this helps.


From contributor B:
With a quarter inch bit you want to run your CNC around 20K. I tend to agree with the other person who recommended to run at 150 ipm. You may even go as low as 75 to 100 ipm. Now you have to consider that acrylic has a very low melt point (around 300 degrees F). If you are making cuts deep in the inside of your blank or sheet, you may have to do a finish pass. Also if you can use coolant it helps a lot.

I know it takes more time but I would suggest that you make a rough pass with a bigger radius bit and trim with your O-flute bit. (I would tend to use a 1/2" bit for all cuts unless this going to screw up your nesting arrangement. You would be able to roughly double your feed rate with a 1/2" bit and it will be able to take a larger chip load). This will give you the best finish. If you can run coolant also, you can make the cut glass smooth without flaming the edge of the acrylic.