part off tools for plexi/PC

[ratindahat]

Hey all,

So i am having some issues parting off some acrylic and polycarbonate parts. I'm just curious what tools or inserts you all are using. The rod i am parting off is ~3/8" - 1/2" diameter. This is on a CNC lathe, so it isn't being fed by hand.

The acrylic seems to want to grab and makes nice noises when it does so. The final part ends up being chipped out.

Thanks for the suggestions.

[Geof]

There are two potential problems parting acrylic. One is that if the tool has any top rake it will tend to dig in, actually on small diameters to acrylic will tend to climb up onto the tool. The second problem is the chips getting stuck in the groove, getting hot and soft and tending to weld back onto the sides of the groov again causing it to ride up. The welding effect is exacerbated with extruded acrylic.

Try using a freshly sharpened HSS parting tool with zero top rake, even a little bit of negative rake and lubricate it with a bit of soap solution.

[RomanLini]

You might be able to improve it with some changes to the tool path? I'm not a machinist but I do mess with machining plastics and some difficult materials.

For some difficult parting I have found a good result was to add some left-right movement to the process so the cut was 1.5x the width of the tool. This gives room room for chip evacuation and you can run an angled or v-toothed profile on the parting tool and use more rake as the sideways movement (and the tool shape) makes the chips much smaller than a flat parting tool just plunging in.

The good thing about acrylic is that tool wear is not really an issue so you can mess with tool shape and likewise it's a soft material so you can add the extra sideways movement without really increasing job time.