I’ve had my PRO4896 for several years now, and up until recently, I’ve never broken a 1/4" endmill. Recently, the Porter Cable 7518 that I had on the machine died, so I replaced it with a Triton 3.25HP router. Same horsepower, same dimensions as far as I can tell. Since then, I’ve been snapping endm…

I would suspect a bad collet, maybe some burs on the inside, right at the edge.

Those are light cuts, I would think it is a tool holding issue. Can you tell if the tool is slipping before it breaks? Is it breaking at the collet?

It’s reliably breaking right at the collet. No slipping as far as I can tell.

No, it doesn’t happen immediately, it’s not super predictable. Could break in 30 seconds, could break in 15min. I haven’t re-trammed, but I didn’t touch the router mount since swapping out the router, but before that it was within a thousandth. I guess I’ll check that again tomorrow but I have a har…

[image] shopratsneedshopcats: cutting plywood at 40ipm, 0.166" I suspect this is the problem. This is a very slow move speed. I bet you’re cooking the bits and snapping them that way. I’d increase move speed to at a MINIMUM of 150 IPM at about 12-14k RPM with a minimum DOC of .25. You have t…

I think Eric is exactly right. I had this happen to me a few years ago before I fully committed to learning about feeds and speeds. It’s counterintuitive and can be scary, but faster is sometimes better. The other thing to consider is the router’s torque curve. When you reduce the speed on a rou…

Usual preface: I’m with PreciseBits, so while I try to only post general information take everything I say with the understanding that I have a bias. It’s almost certainly a bad or wrong collet. Barring edge cases like a large amount of runout on a very long tool breaking at the collet face is in o…

I tip my hat to you sir, once again an excellent and thorough response!

[image] jjneeb: I would suspect a bad collet, maybe some burs on the inside, right at the edge. As usual, I think you’re right. I polished/burnished the inner lip of the collet, and haven’t had issues since. Thanks everyone for the advice!

I had one a couple weeks ago that couldn’t hang on to a half inch end mill. I looked inside and it had a couple of burs. Not sure how they got there, but I tossed it and got a new one. Problem solved.

Breaking endmills

pketcham March 4, 2024, 3:28am 4

can you give us more details? Does it happen immediately? In a corner? Etc. did you re-tram your spindle when you made the change?

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Breaking endmills

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