1/4" Down cut end mill pulling router down?

Thats impossible right?

Ive been carving some valet trays using a 1/4" Down cut 2 flute endmill. 3 times I had issues where I thought the bit was slipping out of the collet and cutting all the way through the material. I had to hit the stop button, the noise was terrible. The last time I ran it, i made sure it was extremely tight. It happened again, but I couldn’t tell that the end mill actually moved in the collet.

My question is, the bit cant grab and pull the router down can it? I have little experience with down cutting but I wouldn’t think the end mill could pull itself down into the material against the will of the Nema 23 on the Z axis.

I thought maybe my collet was bad, but I can run other 1/4" bits just fine. So its either the endmill itself, (I should mic it and verify the OD tonight) or what I described above, if that is even possible.

Any ideas? Im just wondering if anyone else has experience this or something similar

Yeah I would mic it and see. The downcut would actually want to push the endmill upwards into the collet. And upcut would do the opposite and either want to pull the material UP (which is why an upcut leaves a not so desired top finish and frays) or yank the endmill down out of your collet.

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paul Another thing to try is to remove the collet nut and THROUGHLY clean the collet, the area where the collet fits in the router, and take some mineral spirits or denatured alcohol and and clean the shaft of the bit. Then reinstall the bit, tighten it down securely and give it a try on some scrap. Another thing that might be causing the problem is taking too deep of a cut per pass. Might want to check that. Hope this helps.

Thanks Paul, I 100% of the time remove the collet and nut and blow it off with air. But I have never cleaned up into the router spindle itself. That is a good point, I’ll do that tonight.

Thanks for the comments, everyone

Have you checked your router speed control??? When mine made a “terrible” noise it was because the speed control wheel went all the way to the highest number.