Cutting Polycarbonate

[kyle]

I am new to machining plastics, I would greatly appreciate anyones help with speeds and feeds, type of cutter to use, depth cuts and stepovers.

Thanks in advance.

[Rekd™]

Hey kyle

 

Polycarb (lexan) is tricky some times. It will chip when you break out of walls, so try to always cut into the material. Speeds/Feeds are fairly high, as well as DOC and step over. Try around 400-600 SF and a .003 to .005 chip load. Keep it flooded, it will melt, especially if you're not feeding it hard enough. (I had a guy rapid a fly cutter .100 deep into a piece of poly, all the way across. The chip load was .12 as measured by my calipeters. It made it thru, didn't waste the cutter or the part. Trevor may remember him.. I won't mention any names, but his initials are Steve Johnson.)

 

For drilling, use 135° deg tips, not the standard 118°. It helps prevent chipping on the back side of the hole.

 

It's not bad stuff to machine as long as you follow these basic rules.

 

'Rekd teh almost rum thirty

[skeetboy25]

what rekd said, if you can flood this stuff do it. In my experience polycarb behaves best when you dont exceed 1/2 cutter width (on an endmill) on your passes, If you go too deep even with coolant you will get this weird ball of molten plastic on you end mill that WILL ruin the finish on your side walls.

 

If this is for optical and you are woried about staining it with coolant don't exceed 4000 rpms and slow down your feed. This turns cutting into a sort of precision chipping exercise that works surprisingly well.

 

Remember, this stuff is chemically identical to bullet proof glass, so you have a little more licence to abuse it than you would acrylic.

[George_Gerhard]

Polycarbonate

I have many customers machining this material. You can machine 3/8 thick poly with an 1/4 dia. Onsrud cutter #63-725 at 18,000 rpm and 275 ipm, and no coolant.

[kyle]

thx for the help guys...one limitation we have is no coolant, we will be cutting on a bostomatic graphite mill, plus have to go down a 1/64 for some small corners. Again thx for the help and the quick respones.

[Kevangel]

If you are fly-cutting, use LOTS of positive rake to keep from getting chipping action, hard to explain, but you want to cut material not chip it off. Coolant really helps, if only from a cheap spray bottle. Also more expensive end mills seem to cut more uniformly if optical clarity is an issue. If optical clarity is an issue,Mcmaster-Carr (on internet) sells plastic polish to remove scratches(in old days we use to vapor polish before knew un- healthy). Polishing with wet and dry 600 grit before polish and you can make part clear in a hurry, especially if polishing with orbital car polisher (new pad).

[Rekd™]

You can also polish with an oxy-helium flame. Similar to Oxy-acetalyne, but you get the bennies of doing the high pitched voices like with inhaling helium baloons...

 

'Rekd teh 38 going on 13

[MACHINEMASTERG]

ive got one thing to add we cut alot of this stuff... climb mill and then conventional mill back makes for a reel nice finish also abs primer wiped on the surface cleans up and unwanted marks ...

[Harryman]

Use super sharp cutters.

 

This is probably obvious, but I've seen guys reach for the dull ones when cutting plastic.