Questions about milling Acetal and FR4

I plan to use #102 and #282 end mills to machine Acetal and FR4 (in the future, will probably machine polycarbonate). The material will have a thickness of around 2-2.5mm, but I plan to use a surfacing finish to bring it down to 1.6mm or 1.5mm. The materials will be mounted on MDF board that’s 1/4" thick with double-sided tape.

I noticed the depth per pass for the #102 is 1.27mm and 0.610mm for the #282 however. Is it ok to make the depth per pass 2.5mm? That would cut down on the machining time significantly, but I’m not sure if it will break the end mills.

If anyone has a simple table of all the recommended settings for all materials based on the end mill being used, that would be helpful as well.

The feeds/speeds on the wiki/chart/Carbide Create are a bit on the conservative side. You could probably ramp up the DOC, but maybe go a bit slower on the feed rate to get a similar chip removal rate.
You may break endmills, but that’s how we learn. Grab some cheapo ones from online to learn with.

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General rule for low melting point plastics is to keep your feed rate high to avoid local heating and melting, use dust extraction to get the static-cling chips away too. Start with low depth of cut going fast (1500mm/min or more) and slowly increase the DoC based on how it sounds.

On the FR4, if that’s the glass fibre PCB material I believe that the dust from this can be very very bad for you, see this thread


Oh, I’m aware about the dust. My vacuum has a HEPA filter and I have N95 masks. I plan to buy a reusable mask with replaceable filters once I have the money.

I bought single sided and double sided FR1 boards so I wouldn’t have to deal with the fiberglass.

Unfortunately, in the 5 years I’ve had them, I haven’t used them yet. :confused:. But they look nice.

For what it’s worth I have a nomad 3 (which I understand is a good bit more rigid than a shapeoko)

But I just did a quick test cutting natural delrin(a bit stiffer than regular acetal). I ran the shapeoko acrylic presets for the 102 and cut 3 lines at various DOC: 1.143mm, 1.75mm, and 2.5mm.

They all cut just fine but the machine did sound a bit angry at 2.5mm. All this is to say that I don’t know enough about the differences in the machines to say this was a “good” test…but it does indicate that you shouldn’t be too scared of trying stuff out. I think you can probably hone in on a recipe that works well for you without being too concerned with catastrophic failure :slightly_smiling_face:

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Thanks for the feedback everyone! I’ll definitely tinker with the settings a bit.

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