Odd Chip Packing

I have been cutting lots of items out of 1/2” hdpe for last few months and updated feed and speeds based on feedback here as well as from Amana and tools today. Everything was working great and then today I started cutting same file same bit etc but you could tell something was running rougher than normal. The first cut looked normal where chips flew out and then when it went for next pass they just starting packing into the tool path. I took some photos of how the pieces looked after and the chips just packed onto piece so tight I had to scrape them off. Any ideas on what could cause this? It it machine related or router or material? Very odd given how nice other pieces have been cutting.

Thanks for any advice in advance.


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semi-dull endmill ? Have you inspected its flutes with a loupe ?

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Tried two different bits. Pretty much brand new same result. O Flute 1/8 Inch Cutter Up Cut Spiral End Mill

I have never cut HDPE but to my inexperienced eye for plastics, those chips look a little small to me. Wispy chips will tend stick together and get stuck down in slots pretty easily. Not sure what tool you are using but when I use my single flutes on delrin I get much larger chips and never have any issues with chip re-cutting. What is your chip load?

Yeah something is up. Going to keep trying to narrow it down.

Is it colder or dryer where you are today than usual?

You know I thought about that but brushed it off. It has been cooler but still in my garage. I messed with my belts the other day trying to tighten them to no avail. Seem pretty tight already.

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How are you doing dust extraction?

When cold & dry the static buildup on small chips on plastic can be very significant. It might be worth hitting pause every few inches and manually clearing the chips to see if it’s just accumulated weight of chips in the slot.

That could be something. I notice I have chips sticking to rails far more than a week or so ago. I just hooked up my old suck it with a little cyclone on Home Depot bucket.

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So I tried new specktra coated Amana bit and same result. Sped up dial on router and slowed it down and same result. Changed feed speed up and down slightly and same result. Grounded machine vac rails etc same result. Ugh this is confusing as it used to cut like butter and leave clean tool path.

Going to contact Amana or tools today and see if an engineer can assist with photos I have and data on feeds etc.

How much faster, can you share your values ?
My motto for HDPE is “when in doubt, feed (much) faster”.

I have only cut hdpe once but could it be heat related?
The chips are heating up to much and slightly melt together before being evacuated out of the cut channel? Any material on the bit after cutting?

Those chips still look really small to me. What is your DOC? If you could share your feeds & speeds it would be really helpful.

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What bit?

Here is feed and speed data

I saw that.
Was the router set at 18k?
What end mill?

I have the dewalt set near the 2 and the end mill is Amana Tool 51446-K Spektra Coated SC Spiral O Single Flute Plastic Cutting 1/8 D x 3/4 CH x 1/4 SHK x 2-1/2 Inch Long Up-Cut CNC Router Bit with Mirror Finish

Try to feed faster. I’d go at least 100in/min. You can reduce the DOC to .0625. If it seems to handle it without issue (I’m guessing you will), increase the DOC some more.
You can also use the feedrate override to increase, but I’d start at 100.


Will give it a shot and report back