Polycarbonate with Amana plastic bits

CNC Machines Shapeoko
1

I have the Amana plastic cutting bits and I have the S&F dialed in pretty good on the 1/4 bit, but I am having a hell of a time getting the 1/8 bit dialed in. I am getting a good amount of burrs left on the poly, and I have the speed dialed in to be the least terrible it can be.

Here is the 1/4 settings:

  • Stepover - 30%
  • DOC - .02
  • Plunge/Feed - 80 IPM
  • RPM - 11000

I’m using the same settings for the 1/8. If I go faster or slower on the feed the burrs look worse. If I reduce the DOC, it looks worse.

Any idea?

2

Can we get some pictures of your results? Are you climb or conventional milling? Are you doing 2d full width contour cuts or just pocketing?

3

I’m using a pocket and AFAIK, I’m using conventional milling.

Here is the 1/4 cut:

1-4
1-41180×2360 89.1 KB

Here is the least worse 1/8 cut:

1-8
1-81026×2016 63.2 KB

4

What RPM does Amana suggest for the 1/8" ?
That would need twice the RPM of the 1/4" bit to have the same surface speed.

Also, are you running dust extraction? It looks like the bottom of the cut is melting which could be chips re-cutting and getting melted and stirred.

5

I am using dust collection with the sweepy and shop vac. It normally recommends for most plastics 18000 RPM, but the tool has note of:

Use the slowest suggested feed rates and the shortest bits necessary for cutting and routing Lexan.

I’ve seen other recommendations elsewhere for 10-11k RPM. Just tried going at 18-21k RPM and I’m getting the same behavior.

6

I found something that works, but I dont know if it’s correct. I slowed the feed rate down substantially and it seems to leave a smooth cut.

Here are the settings with the 1/8 bit:
Step: 30%
DOC: 0.04
Plunge: 10
Feed: 14
RPM: 10000

7

which Amana endmill is it ?

8

It’s from the plastic cutting kit sold by C3D:

  • #51404-K .25" Single flute up cut
  • #51411-K .125" Single flute up cut
1 Like
9

Here are a few video captures of me using that same 51411-K in acrylic, at 16.000RPM & 54ipm, which translates to 10.000RPM and ~33ipm, and getting half-decent cuts but with some level of chip packing in the slots

14ipm@10000RPM on that single flute is a 0.0014" chipload, which is ok (one can usually pull off several times that in acrylic, but at least it’s not rubbing…)

Are you using dust collection ?

EDIT: Amana says 70 to 110ipm at 18000RPM, so 38 to 60ipm at 10000RPM would be the sweet spot for them

image
image772×785 145 KB

1 Like
10

I think you mean 0.0014"

2 Likes
11

Shoot. Yes I do mean 0.0014", corrected, thanks !

12

For comparison, Amana is recommending a chipload of 0.0039" to 0.0061 at a 1/8" DOC. You are at 0.0014" chipload at only 0.04" DOC. I would be very comfortable cutting at 70 IPM and 18000 RPM at 0.06 DOC and I bet you could go deeper. This is something like 300% faster material removal than what you are doing. I bet you are getting the burr because the plastic is melting a bit. Going fast is almost always the key with plastics.

1 Like
13

That would have been my initial recommendation (“in plastics, when in doubt feed faster”), but he said

which has me puzzled.

14

My guess is that it still wasn’t fast enough. More depth may also help.

2 Likes
15

Plastics like high feed.
Are you trying to get a clean pocket or a profile cut?

1 Like
16

I can’t seem to get more than 20 IPM at 18k RPM with the 1/8” bit. I cut some acrylic over the weekend and tried going faster, 60-70 IPM at 18k, and the cut ended up looking like a snow cone.

17

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