Endmills Creeping Out

Hi, I’ve recently completed construction of the burly mpcnc and until today was having no problems. It works great cutting vinyl and foam, wood not so much. I’ve been trying to run a linear pocketing operation in estlcam to take 3 mm off a sheet of aspen wood. The cuts start great with nice chips but inevitably either the z-axis or the endmill (probably endmill) begins to drop. The dropping accelerates rapidly and within about 15 seconds of it starting the endmill gets stuck deep and yanked out of the chuck. I can now recognize when it begins and stop the cutting in time before things get extreme.

The endmill I am using is the single flute upcut from this set:https://www.amazon.com/gp/product/B07FGFHTG8/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
(I found the fluted section to be 3mm and the shank 3.18 mm)

My machine dimensions are 3’x2’x3’’ and I’ve made sure everything is tight, especially cranking down on the chuck. I’m using the Dewalt 660 router.

These are my latest settings, I’ve also tried at 2mm and 1mm depth per pass with similar results: endmill drops-> chips fail to clear-> endmill gets stuck.

Pictured are some failed 3mm cuts, the gouging sideways only happens when the endmill is barely hanging on to the chuck, the bottom cut was done first.

Frankly, I’m amazed the endmills don’t just snap when this happens but they still seem ‘good’ as new so I’d appreciate any advice you could give me to get things cutting right, thanks.

I run my 2 flute windmills at around 1000mm/s (~16.5mm/s). With a single flute, federates are normally slower as you are taking half as many bites out the material. It’s possible that you are pushing it too hard. Perhaps try flowing the feedrate [F(xy)] down a bit.

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Thanks I will give that a shot

And my endmills too. Autocorrect must think I’m Don Quixote or something.


On my lowrider once the dropped bit happened in the collet it was game over for the collet. I tried a variety of things including tightening the thing as hard as I dared with no change in fortune.

A few seconds into any cutting out popped the bit. This was on the dewalt 611. I used the elaire one from the store. I figure I must have done something to cause the initial issue. New collet solved my issues.


I’ll try out some new ones and see if that does it. At least they’re not very expensive.

Might be worth it to make sure there’s nothing caught in the grooves of the collet itself, maybe blow it out with compressed air. If there’s dust in those channels it can prevent the collet from tightening fully on the shaft of the tool. I also run an old toothbrush around inside the collet holder every once in a while.


Make sure that are not 3mm mills

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That was it. One end of the collet had gotten all torn up when the bit first slipped and the channels were full of metal. While I wait for new ones I’ve cleared the grooves with a shim, flipped the collet, and reduced the stepover. It held on for the 2 hour job after fairly well with no creeping. Thanks to everyone for helping me clear that up.


Check the collet for anti corrosion coating. Some of our collets that come in are coated with a heavy coating that prevents proper tightening and often result in wobbly loose bits.