Hi, folks. Does anybody know the SFPM for calculating speeds and feeds for machining acrylic? I need to drill some #6-32 and #10-32 thru-holes, and do a little lathe turning on some 1/4" material. thanks!
All I found was this: http://www.plasticsmag.com/features.asp?fIssue=Sep/Oct-01 Most of my plastics work is by my rule of thumb... play with a bit and see...
For speeds, use anything that is reasonable, it's plastic, it really doesn't matter too much. For small holes like that, I'd probably just run it about 1000 RPM, and try to keep a little bit of a spray of coolant on it, even if you have to use a spray bottle or the like. Yes, you could go way way faster, but since you're not doing production, it really isn't going to increase production much, and if you run too many more RPM it will just make a mess with the coolant. If you follow just one piece of advice from the page Greg posted.... make sure to BACK UP THE SHEET with something or it will definitly crack when the bit breaks through!![] Instead of going through all of the trouble shapening the drill bits as suggested, you might try to just put a small flat on the leading edge of the drill bit to keep it from digging in so much. don't create a rounded or dull edge, just a small flat so that the leading edge of the bit is at about 90 degrees or less to the workpiece, and comes to a crisp corner at the point that it contacts the workpiece. Then try it on a scrap piece until you get the desired effect. Other than the drills, make sure to use sharp tools, especially when turning!
Without coolant, get the slowest speed you can manage... otherwise deal with melting issues. For the through holes... very fine (slow) speed near breakthrough. It seems to me that twist drills like to push out a burr, and then grab the burr upon exit, this shatters acrylic. A step drill works wonders for riser holes btw If you don't like coolant... try compressed air. Should help a bit Mike
