End mill holders are designed to hold end mills. Collets are workholding
devices. That said, you can use a collet to hold an end mill. The problem
is that there's no way to lock the end mill in the collet to prevent it from
sucking out while cutting. That could ruin a work piece in which you'd
invested a lot of time. You can probably get away with it indefinitely on
a small machine taking light cuts, but it is something to consider.

Gary


Although there are some collets specifically designed to hold end mills. Don't
know if they are available in R8 or not, but I have a couple of 40 taper collet
chucks for my horizontal mill that take TG100 collets. Most of the collets are
plain, but some are "No Pull" styles which have a plug that locks into the flat
on a Weldon shank. Can't use them on a regular shank, though, unless you
remove the plug.

John Martin