Bits for cutting ABS/PC plastic at 1/8 inch thickness

I plan to use the Makita RT0701C spindle for my MPCNC. The CNC will be 1’x1’ with steel piping so it should be fairly sturdy.

What bits do you reckon will work with the plastic of this thickness.

Will 1/32 inch or 1mm be too small to realistically cut plastic? What is the smallest bit I can use, and what is the smallest V bit I can use (The ones that are like v carvers and drill bits at the same time)

Plastic is hard. It can start to melt and that’s the end of your cut. You’ll need plenty of air to keep the cut cool, and blow the chips out. Smallest I’ve done so far is 1/8th inch.

Interesting question. I haven’t read much about cutting plastic, but a smaller mill will have a lower surface speed (tangential speed) for a given rpm. That COULD translate into less heat. I’d also expect smaller mills to have smaller flutes, which increases the likelihood of chip-packing. That COULD translate into more heat.

It still wont be as bad as a laser right?

I have no idea what “bad as a laser” means. When I suggested you post your bit issues as a separate question, I was hoping someone with extensive plastic milling experience would respond. I’m confident you can find a recipe and bit combo that would cut your material down to 1.5mm, and it possible you can go smaller. You may need a specialty plastics bit, but I would start with standard flat endmills with 1 or 2 flutes, and I would try some burr engraving bits as well. Based on some acrylics cutting done by others on the Shapeoko, I’d start with this recipe:

  • 1 or 2 flute endmills
  • 1.0 to 1.5 (8,500 rpm to 10,000 rpm) setting on the Makita
  • Cutting feedrate of 1100 to 1800 mm/min
  • Start with 0.5 mm depth of cut

V-bits are a different item. The angle of the v-bits and the depth it cuts determines the top width of the cut. You can make fine shallow lines with high-quality large v-bits as long as you have your machine and spoil board tuned so that the depth of the cut remains constant. Without knowing what you are trying to make with your MPCNC, it is hard to make specific v-bit recommendations.

I’m curious enough about cutting plastic that when my current project is off the machine (likely tomorrow) , I’ll toss a piece of extruded scrap acrylic on the machine and try to machine it with some smaller bits. It won’t be your specific plastic, but it will give you and idea.

You want spiral endmills. The flat ones will clog and fuse pretty much instantly.

So the project I was cutting failed and there was not enough time to start over, so I ran a couple of tests. The only bits I had that were worth testing in the sizes you are looking for were a 2mm single flute ball nose endmill, a 1.5mm burr/engraving endmill, and a 60 degree v-bit. I ran the test using the Makita setting of 1.5 and a feedrate of 1100 mm/min. I used a scrap of extruded acrylic 2.8mm thick and a 0.5mm depth of cut.

The single flute endmill cut well, nice large chips, no melting. Edge finish varied from pretty nice on straight cuts to somewhat rough on curves. I did not run a finishing pass.

The burr/engraving bit did not do well. Even at the specified feedrate, some plastic was melted to the bit by the time I finished a single straight cut.

The v-bit did okay. All the lines were “etched” correctly, but there was dust left in the cut. I cleaned some of it out. Looking at the bottom of the ‘o’ and ‘v’ and the connection to the ‘e’, you can see how fine a line can be etched using a v-bit.

I mean heat wise. The laser was really hot and melted my plastic. Is a CNC less hot I assume?

I’ve been given a piece of some kind of sheet plastic that was cut on a glow forge and the edges look very good and I don’t see any signs of burning like on laser cut wood.

I am guessing the key is to vaporize the plastic instead of melting it. So you need a lot more heat than just to melt it.

Yes, though in the case of ABS, when you reach the heat to vaporize it, it burns, so its sort of a game getting the right speed and intensity with the laser to try not to burn it and not to melt it.

Never laser ABS! The chlorine gas it releases is bad for you, and worse for the laser’s optics.

You really want single flute so the chips are larger. You also want to run as quick as you can.

Try: .25 endmill, single flute
Rpm: 12500
Doc: max .4

And keep it cool and clean.

My good friend its not chlorine gas with ABS, it Hydrogen Cyanide (HCN). Cl is not present in Acrylonitrile butadiene styrene. The chemical formula for Acrylonitrile has a CN in it. Which if anything is much worse than chlorine gas for health, not sure about laser optics

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Ahh, yea, that’s it. Still bad for the optics.

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Also a question of the beam’s shape along it’s path through the material. It mostly starts with people setting the depth of maximal heat just to the surface (on wood), being deceived by the nice narrow spot / line when zeroing Z. The maximum heat, i.e. the narrowest focal spot should be deep enough under the surface, so that the cone on the beam’s entering side still is hot enough to vaporize the material. The same applies to the outgoing / lower side. If you can’t reach the lower surface in one pass, you’ll have to add more.
Jeff, wood gets also vaporized, but the beam has an energy gradient over it’s radius. From a certain distance from the center, the energy is not enough to vaporize the solid parts, that’s where the charcoal generation starts. BTW, a very bad surface for later glueing. Sandblasting or sanding it off is tedious but helps.
Spraying coolants on to our modern sintered bits is not the best idea, that can lead to microfissures. Lots of air are fine, except for the proliferation of dust in all directions. A powerful directed air stream combined with an effective dust vac is optimal, but not that easy to achieve.

I don’t think our bits are sintered and I don’t think coolant is bad for them.

All carbide is sintered, but I don’t think coolant will hurt them unless you get them hot, then start spraying coolant.


See here. Or just googoolate ‘milling bits vhm sintered’.

Sure. But you won’t try to cool a not-hot bit. If it needs cooling to work (or not), it’s hot by its own measure, I think. Or the measure of the heated operator.

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Unless you were cooling it from the start, right?