Molten hdpe, help a noob

Wondered what I can do better working with hdpe. First attempt at cutting plastics ended in molten goo stuck to the bit. Here is my feeds and speeds:

Feed: 400 mm per minute
Depth per pass: 1mm
Bit: 1/8th’ upcut flat end mill
Spindle Rpm: 12,000 (2 on makita router)

I figured that was plenty slow RPM wise. Do I just need to feed alot faster? It also cut the same small area multiple times trying to cut out a 1.5’ cylinder. Wonder if that was just heat build up.

Well, the feeds and speeds chart: (EDIT: Note that that URL no longer works, use: instead) suggests:


Feed: 2032 mm (80" / min.)
Depth per pass: 3.18 mm (0.125")
(these are for a 1/4" endmill)
RPM: 21,500 (4 on a Makita)

More on it at:

It sounds as if you’re very close to the very conservative specs on the wiki — also check your belt tension and pulley set screws, they’re a frequent cause of early difficulties, see: — it could be that the system got bogged down due to the stuff melting, but I’d suspect more likely that it was a lost step resulting in a too small a pass being made which resulted in things gumming up.

Wow thats quite a bit different. You are correct. I was going off the materials wiki, there was a conservative feed and speed. I didn’t realize that chart existed though. I will try that next.

I will take a look at my belts as well. The cut itself however turned out very well. I measured the circle to exactly 1.5’. just the top edge of the cut melted and made an umbrella around the endmill

The top of that page notes:

The values below may be used in configuring milling operations when using a CAM program to generate G-code to make a cut, but unless your machine is essentially identical to the machine which they were used on, can be considered as only very general guidelines. All values should be verified and tested on a scrap of material first, then one should adjust to match desired chip size and surface finish and time required for completion.

and that chart is copied in there, converted to metric at: thanks to @markwal

Please note however that there seem to be some oddities in the chart in terms of RPM and settings for the various routers — opened up a ticket w/ @ApolloCrowe but still waiting on things to get sorted out.

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I recomend using the .25" cutter and the feeds and speeds chart mentioned by @WillAdams above:

This is what cutting HDPE with the 3 flute .25" cutter looks like:

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Wow, that chip removal tho :+1: . All i wanna do now is make it snow. Excited to give that a try when I get home.

That said, I have done a fair bit of cutting with the less than optimal speeds w/ a 1/8" endmill — curious what G-wizard would suggest, and really would like to see a version of the Carbide 3D chart for 1/8" endmills in an SO3.

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Can we kickstart a set of feeds/speeds charts for all the cutters Carbide3D sells, for both platforms?


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Well, that’s sort of what we’ve been trying to do on the Materials page on the wiki — I’ve been thinking that over a bit, and I think I’ve got a layout / format which we can use to help make this a bit more workable and tidy up the page a bit.

I’d like to get the numbers for the 1/4" endmills cleaned up first though.

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The first thing I ever cut on my XXL was HDPE…it’ll make snow…and if you don’t vacuum it up you will find snow in the Summer months, in places you didn’t even know existed in your shop. It’s really awesome to watch it cut that stuff!


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I’ve been having a go doing this recently and had the same issue - I found when using a 1/8 bit It quickly gooped up. I was conservative like yourself and went slower and also shallower but to not much avail.

After changing speeds and settings I had almost given up, that was until I tried a proper cutting bit for plastics - a single fluted bit - I tell you what it worked like magic - cut clean and gave a great finish like in the video.

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I cut plastics almost exclusively. Here is a great guide.

My setup is SO3, Dewalt 611 router, KENT CNC Mini Shoe, Shop Vac. I engrave with a 0.010 endmill and profile with a 0.312 endmill. Router set to 1 (Lowest setting)

RPM x # of Flutes x diameter of bit x chip load (.03-.04 for plastics)

My feed Rates
16,000 x 2 x 0.010 x 0.03 = 9.6 IPM for the 0.010 endmill
16,000 x 2 x 0.312 x 0.04 = 29.95 IPM for the 0.0312 endmill