# Inch ER40 Collets...What?!



## thestelster (May 11, 2022)

Sometimes, actually often, you don't know what you don't know.  Many years ago I purchased an ER40 collet set to fit my milling machine in NMTB40.  I was thrilled that the set would hold everything from 3mm-26mm.  And since the collets were collapsible by 1mm, I was golden, even if all my cutters were Std shanks.  Through all this time, holding some cutters, I had to really screw the collet nut in quite a bit for it to grab.  I didn't think anything of it.  Then I read this:
By MariTool

It is always the best to use the max size shank tool for the max size collet. For example if you need to hold a .625 endmill it is aways best to use a collet that has a range of .625-.586 which is called a 5/8 collet. You can easily use a 16mm collet which has a .6299-.591 capacity for a 5/8 shank tool. I do it all the time with no problem. I guess you just have to keep in mind the more you compress a collet the less clamping you will have. I would say a 10-15% reduction. Concentricity should be the same.

So I looked around, and sure enough, inch sized collets.  So I ordered a few.  Son of a gun!!  The cutters fit snugly in the collets.  Well, time to order more inch collets.


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## Dabbler (May 11, 2022)

My er40 collet set is inch, but I need to fill in the gaps - about 8 collets.  One day I'll get a full metric set also...


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## thestelster (May 11, 2022)

Dabbler said:


> My er40 collet set is inch, but I need to fill in the gaps - about 8 collets.  One day I'll get a full metric set also...


I even have a 19.5mm collet because the 19mm was just a little too tight for 3/4" cutters.


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