I recently used a metric 3-4 mm collet for holding a 1/8" carbide endmill (couldn't quite jam it in a 2-3mm one).
From the off, despite my best efforts it proved to be very difficult to lock into position. The first endmill just about stood up to it and after some use blunted and eventually broke. My second endmill lasted a matter of minutes before breaking on the edge of the material. I surmised that as it engaged the edge it got pulled downward from the collet which increased the depth of cut overloading and breaking the part.
I had the forsight to know I was likely to have issues and had already ordered a 1/8" collet for that purpose. It arrived this morning with the obvious benefit of only having to tighten with reasonable force. The unobvious benefit was the significant improvement in a mirror like surface finish.
So I guess the moral is just cos it says 3-4 mm on the collet doesn't mean you should believe it - especially for the very small sizes.
Hope this is of some benefit.. .
picclock
From the off, despite my best efforts it proved to be very difficult to lock into position. The first endmill just about stood up to it and after some use blunted and eventually broke. My second endmill lasted a matter of minutes before breaking on the edge of the material. I surmised that as it engaged the edge it got pulled downward from the collet which increased the depth of cut overloading and breaking the part.
I had the forsight to know I was likely to have issues and had already ordered a 1/8" collet for that purpose. It arrived this morning with the obvious benefit of only having to tighten with reasonable force. The unobvious benefit was the significant improvement in a mirror like surface finish.
So I guess the moral is just cos it says 3-4 mm on the collet doesn't mean you should believe it - especially for the very small sizes.
Hope this is of some benefit.. .
picclock