Acrylic Cutting Help

[Tenson]

Hi Jonathan,

I had it pretty well clamped I think. Please remember the roughness doesn't seems recessed from the rest of the cut, so possibly not just re-cut chips embedded in it?

I was using:

700mm/min
11,000RPM
2 flute 3.17mm cutter
1mm multiple passes
0.3mm finishing pass

I'm not sure how it would have lost position at such a low feedrate. I guess I might need to check the rotating ballnuts to make sure the cogs aren't working loose.

By the way I got my vacuum extraction working just the other day.

[m.marino]

Increase feed rate a bit. With that type of pass in acrylic you want to be getting chips that are quasi snowflakes to proper chip form. Dust is a sign that you are cutting to slow and you will deal with melt and it will cause problems. Next is this cast or extruded acrylic (easiest way to tell that I know of is almost all extruded has a translucent protective covering and cast is white) When I am surfacing 1212 I am going between .75 to 1.5 mm deep with a 3 flue TCT MG end mill and running it at about 14K and 2.3 m/min and getting rather nice finish. Acrylic is a problem child in that it will melt easily IF F & S is to slow (even cast will start too but requires really slow).

Cutting plastics requires testing and learning what works, due to large number of variables that are out there. Type of plastic, type of end mill, S & F's; these all play a part then add how rigid is the machine and things get interesting.

Michael

PS From everything I have seen I agree with ADCNC that is redeposit of plastic on passes after the original cut due to too slow of feed rate.

[Tenson]

I don't think it is just the feed and speed, since the X axis direction is fine at the same speeds. I suppose increasing feedrate might reduce the need for better extraction though? If I push feedrate too high without increasing RPM of course the bit will deflect or break, it is only 3mm dia.

I can probably improve dust extraction (for one, I emptied my vacuum!). I'll have a play and let you guys know how I get on.

[Tom J]

Just broke last carbide single flute 1/8" 3.175mm bit doing 700mm/min at 10.000 rpm, 600mm/min was ok but still poor finish.

[Rye]

I usually cut acrylic with 1 mm passes using a 3.175mm single-flute @ 1050 mm/min - somewhere between 10000-13000 rpm (i think). Will be cutting some tomorrow. Will post RPM here.

[Tom J]

I usually cut acrylic with 1 mm passes using a 3.175mm single-flute @ 1050 mm/min - somewhere between 10000-13000 rpm (i think). Will be cutting some tomorrow. Will post RPM here.

I follow 50%+ rule of DOC which was 2mm in for 1/8" will try less. Going to buy decent Trend bit 1/4" 6.35mm

[Rye]

I follow 50%+ rule of DOC which was 2mm in for 1/8" will try less. Going to buy decent Trend bit 1/4" 6.35mm

Cut some 4mm acrylic today using a 4mm shank/3 mm dia cut single-flute shop-apt bit. Did two passes @ just under 2mm on each with a finish pass. Feed rate 1200 mm/min with spindle speed around 13200 rpm (220 hz). Cut fine leaving a nice finish (just a couple of tool marks on one side.) Not saying that's the correct or optimal speed, but it worked for me. Usually I stick to smaller passes because I have a habit of not properly sticking/securing the acrylic to the spoil; and there's nothing worse than spending ages engraving acrylic just to have it lift from the table when cutting :)

[magicniner]

Several mentions of "Climb V Conventional" in this thread.
If you are cutting a slot when profile cutting a part there is no climb and conventional, the cut direction only affects the deflection direction toward or away from the part, the cutter is cutting both climb and conventional in alternate halves of it's rotation.
Climb V Conventional only comes in when the cutter is engaging less than 100% of it's width in material,

- Nick

[Tenson]

Okay well I actually found that my entire Z axis was loose from the X axis. Strangely though I'd have expected that to make the X axis cut poor but that one was great, lol. Still it couldn't have helped matters. I've also made a modification to improve dust extraction. I haven't tried another cut yet, I'll do that tomorrow.

I'm also considering getting a more suitable tool for cutting plastics. Looking at the Cutwell Tools site.. what do you think is better for acrylic they have 45deg Helix flutes (do these extract the chips better?) plus some YG single flute HSSE and some Karnasch cutters. Are the Karnasch worth the extra money?

[JAZZCNC]

Are the Karnasch worth the extra money?

Never used any to cut plastics but have in Ali and they are excellent cutters. Best finish I've had from any brand cutter so far.