Not every 1/4 inch endmill is a 1/4 inch

LowRider CNC Advice
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It seems some endmill makers use ‘guy inches’ when they make their tools. I have a brand new endmill, carbide coated, blessed by the pope on high and next in line for the throne in england… that I’ve been saving for a while. Just because what I had was good enough, but I had a couple good projects in the works and decided to switch over. Only to see it drop out part way through a cut. Fortunately I was there, heard the pitch change and shut things down before it did too much damage, so I salvaged the project.

Investigating the issue, once the collet got hot, out she came. I had to heat things up and then really crank things down to keep the bit working. I thought my collet was shot, got a new one, same issue. So I swapped back to a different bit, no issue.

So out with the calipers, and sure enough it’s .23" Good enough for a drill style chuck, but not a collet. And also explains the extra bit of hand work I’ve had to do in order to get parts to fit.

I’ve had this on my shelf for months, don’t remember where I got it. So it’s in my junk pile, lesson learned. Calipers on every new bit before it enters rotation.

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I wonder if this is really a 6mm bit, which would measure 0.236". If so, a 6mm collet would work.

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hi, there are end mills where the shank is slightly smaller than the cutting edge. One reason for this is so that if you want to cut deep, the shank doesn’t “hit” the walls. There are also collet’s available with a diameter of 5-6 mm so it will fit better for those “undersized” shank’s than basic 6mm collet

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That’s almost certainly a 6mm endmill.
6mm = 0.2362"

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More than likely it is a 6mm, they’re selling them as 1/4 inch though. Those sneaky bastards…

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Get a 6mm collet. i have mostly 6mm but a few 1/4 and always use a 6mm collet for the 6 mm just for the reason you found :wink:

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closing old topic to help fight spambots