Advice on machining plastic

[3dlow]

Hey guys,

Figured I might get a good advice from someone on this forum. I'm try to get a good 3d surface finish on some test parts I made. Material is 3D printed PETG which should be similar to machining ABS. I'm using a 2 flute 1/4 ball mill amorphous diamond coated from Harvey. Stepover of the pattern is 0.5mm but i feel i could go a bit higher and not have a scalloping effect. I don't have air cooling at the moment (compressor is defective) but i might try this. It feels like it's re-cutting chips. See pictures ... any advices?

 

[machinedude]

when your 3d milling its a toss up between how fast you want to generate your profile and surface finish quality. if you want a better finish a general rule of thumb would be the slower the feed rate and finer the step over the better the finish you will get. I would slow the feed down first then possible try a finer step over if it's still not giving you a good finish. getting some mist or coolant would help too. cutting dry is not ideal by any means.

 

[jtknives]

When ever I would cut plastic (Delrin and Teflon) on the cnc mill I used 2 or 3 flute super sharp high speed steel endmills. You can also use a shop vac to suck away the chips as thy are cut.

 

[machinedude]

looks like you have an adaptive clearing path to get the bulk of the stock removed that's fine. another thing to would be to leave a small amount of stock for a finish pass with your ball nose. keep what you have for a roughing tool pass and leave maybe .005 or less for the final finish pass at a much slower finish feed rate. you should be able to set stock to be left easy enough with fusion 360 in the radial and axial section of stock to leave.

a shop vac is not a bad idea either as suggested above to keep things clear. chips being recut will never help the situation.