Cutting 2" cast acrylic

[routski]

I am cutting 2" clear cast acrylic. I'm looking for any insight or tips on which bits produce the best results.

Thanks
Larry

[Geof]

Lathe or mill?

I have machined a lot of cast acrylic. Actually I started a thread showing some parts I made years ago: http://www.cnczone.com/forums/showthread.php?t=46464

I found HSS tooling best because you can grind a very keen edge on it. Twenty or more years ago it was not possible to get micrograin carbide that can be sharpened to a razor edge.

These days if you are milling you could probably get the micrograin carbide tools made for aluminum. These should give you a very good finish but you would have to make sure everything was very well clamped. These tools have a high helix and top rake so on acrylic they would grab if there was any flexibility in your setup. I would be very careful trying the mill the perimeter of cast sheet. Regarding speeds I kept down around the sfm you would use for brass; you do not want too much speed because you can get melting of the chips. Feed for milling maybe 0.001 per tooth or less for turning 0.005 per rev or less. With experience you might find you can crank these up.

[ImanCarrot]

Oh, don't clean acrylic with Acetone or Trichloroethane- it'll melt it.

Cast acrylic I find better than extruded- the flaws or impurities in cast all fall to the bottom, but in extruded they're all over the substrate.

Note that if you do see impurities inside sometimes they can be eliminated by annealing the component. I use 80 deg C for 24 hours.

Here's the finish I get on acrylic straight off the diamond turning lathe:

[routski]

I'm cutting acrylic on a MultiCam Router. After more research, and trail & error, a 1/4 dia bit with a 2 1/14 cutting edge will break every time. I'm using a 3/8 & 1/2 dia bit now.

Any suggestions on bits? (straight flute, low helix, 3 flute, etc...) It can get pretty confusing to a rookie!

Larry

[ImanCarrot]

The main problem with acrylic is that it melts if you ramp the RPM up. A two flute end mill is better than a four cos the material is not getting whacked all the time, wind the RPM down and you'll be surprised at the difference (I know it goes against the grain, but it works).

Chip extraction- just use an air hose to get rid of the swarf. If you're para bout not using coolant then lightly spray with WD40/ water mix (50/50) but remember the coolant will react with the material if it's high 'nuff temperature at the cutting face. If you're only using air to get rid of chips make sure you got ventilation- some plastics contain toxic stuff which when vaporised (ie being cut) which can be dodgy- you'll smell it and it smells like a circuit board that's burned out (proly arsenic or something bi-phenol or summit).

If the chips are coming off the machine all melted together then you got the wrong RPM/ Feed Rate- they should be independent chips, not melted together. [edit] What I mean is they should be like fingernail clippings, not welded together in little gnarly clumps... dunno if that makes sense [/edit]

Think of machining plasticine or putty