Quick acrylic edge clean/polish.

[kiwichris]

Did some experimenting...

End result: I just need to put up with what I'm doing till I've got my better machine...

I did a bunch of test cuts at 300, 500 and 900mm/min (Flat out for my current machine). I did them at different revs to compare results....

I also got out my laser tach and discovered that the Dremel was going a lot faster off-load than I thought, and at low speed the revs really drop fast under load. No surprises there really... Top speed is 35k rpm. The lowest setting, which I'd always assumed was 10k, and about 7k loaded it was still 13k rpm but dives to 6k when cutting 1mm into the acrylic.

So.. The best cut was 900mm/min at the lowest revs. No surprises there either, that's what was suggested here, and I've read that same advise a few times on this site and elsewhere when it comes to plastic cutting.

I then tried to cut a profile at that feed & revs.. You can see the result in the first pic. It's the the partially complete rounded off rectangle that goes from left to right and then stops as it starts to arc downwards.

Just about there the revs dropped massively after the change of direction and the dremel stalled, leading to my first tool crash in a while. Pity I didn't have the camera running really. I e-stopped the rig and started to back out the Z manually by turning the lead screw which was about when the wee end mill decided it had had enough and shattered with a loud 'PING'. :-)

Anyway, pics attached of some of the cuts, if only to validate what everyone seems to know already about cutting acrylic. The second engraved cut doesn't look that 'dusty' in reality, I fiddled with contrast and brightness of the photo a bit to show the cut detail. Black on black plastic does not make very interesting photos otherwise!

Two of the pics nicely validate that conventional milling gives a better surface than climb, which is machine cutting 101, but it's nice to see that empirically.

Cheers, Chris H.

[RomanLini]

Thanks for the photos! It looks like a worst case scenario, you are running a real deep cut at full tool width (full WOC) with a less than rigid spindle, and probably poor chip extraction and too-high RPM thrown in!

When cutting out a keyring (say an oval shape) try cutting around the outside exactly 0.5mm too large on all sides. Cut down in much smaller depths of cut, like 0.5mm or 0.75mm DOC each pass. Definitely keep it under 1mm DOC.

Keep running at 900 mm/min as above. Go down to about 0.3 above from the table, which will leave a "skin" easily strong enough to hold the part in place for the final operation.

Then for a final outer cut, cut at the proper size which will be a 0.5mm width of cut. Conventional or climb, whichever seems to work better with your tool. Come down at 1mm DOC per pass, but stop at about 0.15mm above the table, this should leave a "breakout" skin and 0.15mm works pretty good for small parts in acrylic.

Also you might want to try a mister bottle like those small handheld misters you get in the supermarket, people use them to mist plants. Just plain water and a very fine puff of spray every now and then when it's cutting. Combined with the lighter DOC this should end all your melt problems.

Here's a build thread of my DIY plastics mill, it gets a lot fo acrylic use;
DIY hobby small plastics mill/router

[kiwichris]

Hi-ho,

Sorry, I am cutting at 0.5mm DOC, I might have typo'd that somewhere.

But you're right on the other issues, but then I like a challenge. :-)

I'll have a play later in the week with using multiple passes for the profile cut and see if I can bust another end mill.

Cheers, Me.