[qwertysimo]

Hi,

I have problems cutting acrylic - melting and wrong chip formation. Used acrylic is extruded acrylic (Evonik brand). Used cutter is CMT 188.050.51 (5 mm (0.2") single flute solid carbide upcut bit for plastic and aluminium, not listed in CMT catalog any more).



Based on materials I read I started on the bottom of chipload range I hoped that should work but the results are bad. Pictures description:

The first picture - below the black line, actual results of slotting. Above the black line - slots with chips removed. Individual slots:
A - 12.000 RPM, depth of cut 2.5 mm (0.1", half the diameter), chipload 0.1 mm (0.0039"), feed rate 1.200 mm/min (47 IPM)
B - chipload 0.11 mm (0.0043"), feed rate 1.320 mm/min (52 IPM)
C - chipload 0.12 mm (0.0047"), feed rate 1.440 mm/min (57 IPM)
D - chipload 0.13 mm (0.0051"), feed rate 1.560 mm/min (61 IPM)
E - chipload 0.14 mm (0.0055"), feed rate 1.680 mm/min (66 IPM)
F - chipload 0.15 mm (0.0059"), feed rate 1.800 mm/min (71 IPM)

G - 8.000 RPM, depth of cut 2.5 mm (0.1", half the diameter), chipload 0.1 mm (0.0039"), feed rate 800 mm/min (31 IPM)
H - chipload 0.12 mm (0.0047"), feed rate 960 mm/min (38 IPM)

I - 18.000 RPM, depth of cut 2.5 mm (0.1", half the diameter), chipload 0.1 mm (0.0039"), feed rate 1.800 mm/min (71 IPM)

The second picture - details of A - I slots.

The third picture - cleaned slots. I noticed that chips are melted to the left side of the slot (cut direction left to right on the picture). Right side of the slot looks better than the left side.


Can you advice what to try next? Looking at the second picture, it seems to me that chips are not extracted at all from the tool thus recutted and melted.

Am I using incorrect tool? This one is recommended for plastic. Tools is new, sharp.
Should I increase the chipload? I did not like sound of cutting now already and I am afraid to push it more. Or, are chips too large and stuck in the tool?
Should I use different depth of cut? Most of the advisors online suggest to start even with 1xD depth (like Onsrud cutting data sheet for similiar tool).
Should I blow air on tool to support chip extraction? Unfortunately I do not have any air compressor, only a vac with ability to reverse air flow.

I tried to use this tool for full depth finishing pass on one of the edges of the acrylic piece and the result was very good. Produced chips were nice - uniform, no melting observed. It was outside profiling with no obstacles for exiting chips in contrast to slotting described above.

Thanks.

[Andreiir]

Try with 3000 -4000 rpm for spindle .

[ger21]

If the slot width = tool width, then you will have problems, as you need to get the chips out of the cut. Blowing air would help, as would shallower depth of cut to help get the chips out. If possible, go back and take a full depth cleanup pass. A slightly smaller tool, cutting a pcoket, with a full cleanup pass will help to get the chips out.
Also, extruded acrylic is more prone to melting than cast acrylic.

If the machine is rigid enough, a higher chip load may also help.

[nlancaster]

I cut acrylic with an Onsrud 65-25 Single O-flute upcut bit. 24,000RPM at 120IPM, vacuum dust show gets all the chips. Slotting will always leave a few chips behind but not much, and no melting.

Cutting extruded acrylic you will always end up with some chips stuck in the cut. Normally I just scrape them out. Cast acrylic is the way to go! No chips left behind.

Also you could try some pledge furniture polish, it can help with reweld of chips as it will be a lubricant.

[qwertysimo]

Try with 3000 -4000 rpm for spindle .

I have 2.2 kW chinese water cooled spindle that does no have enough torque below 6000 rpm, from what I read. 8k rpm seems to work fine.

If the slot width = tool width, then you will have problems, as you need to get the chips out of the cut. Blowing air would help, as would shallower depth of cut to help get the chips out. If possible, go back and take a full depth cleanup pass. A slightly smaller tool, cutting a pcoket, with a full cleanup pass will help to get the chips out.
Also, extruded acrylic is more prone to melting than cast acrylic.
If the machine is rigid enough, a higher chip load may also help.

Yes, that is was my case, slot width = tool width, slotting. OK, I will try smaller DOC and to blow the air. I will try pocketing with multiple roughing passes and full depth finish pass as well.

Extruded vs cast acrylic - I want to flame polish edges and it works nice with extruded acrylic. While the cast acrylic has higher melting temperature and thus cuts better, what about flame polishing it? I have never used one. Probably a good reason to get sheet of cast acrylic and play with it.

I have a build log opened here. My machine is still not fully completed, but reasonably rigid so far. (I have cut aluminium already.) Higher chipload, hm, I will get a spare bit and try that.

I cut acrylic with an Onsrud 65-25 Single O-flute upcut bit. 24,000RPM at 120IPM, vacuum dust show gets all the chips. Slotting will always leave a few chips behind but not much, and no melting.

Cutting extruded acrylic you will always end up with some chips stuck in the cut. Normally I just scrape them out. Cast acrylic is the way to go! No chips left behind.

Also you could try some pledge furniture polish, it can help with reweld of chips as it will be a lubricant.

I cannot find Onsrud 65-25. Do you mean 65-025? If so, I use very similiar bit and in fact I grabbed recommended chipload data from Onsrud cutting data sheet for 65-000 series.
OK, I will try cast acrylic.

I forgot. I tried to spread little of washing detergent on acrylic before cutting. It might helped a bit, not as much as I hoped.


Thank you all.

[beone]

You need a lube-coolant. Try a 50-50 mix of dish detergent with water. Slather on the acrylic before cut, keeping it wet it will make a world of difference
Dave

[qwertysimo]

You need a lube-coolant. Try a 50-50 mix of dish detergent with water. Slather on the acrylic before cut, keeping it wet it will make a world of difference
Dave

I definitely prefer dry processing, but out of curiosity I will give it a try.


Meanwhile I found information that for extruded acrylic there are single tooth cutters with polished flute with lower risk of clogging. Some have 25 deg lead angle compared to traditional 30 deg, for faster chip extraction I guess.

[awerby]

If you want to cut acrylic dry, get a vortex air chiller: http://www.vortexair.biz/product-cat...cold-air-guns/

[nlancaster]

I rarely use lube, and never use a vortex air chiller. I do not get reweld on my acrylic cutting.

1/4inch Onsrud 65-025 or 65-026, 24000rpm, at 120IPM

90degree vbit at 24000RPM at 100IPM with pledge table cleaner as a lube.

[qwertysimo]

awerby, that vortex air chiller is realy nice!
nlancaster, thanks for your specific info. So your chipload is 0.127 mm (0.005"), all right.

I bought single tooth cutter with polished edge designed specificaly for extruded acrylic.
I set 18.000 rpm with 1.800 mm/min (70 IPM) feed rate, that gives chipload 0.1 mm (0.004"). Shop vac set to minimum power. Roughing and finishing pass (0.15 mm (0.006")). No melting, no smell. The very first cut is just perfect:



Later I will play with chipload to find optimal setting between 0.1 - 0.15 mm (0.004 - 0.006").

Thank you.