It's very important to ensure that the end mill is inserted into the collet at the proper depth. The flutes must be completely exposed to avoid clogging, but the shaft must have the maximum possible length inserted into the collet to avoid dislodging
To insert a tool, first insert the collet into the collet nut, then screw it onto the spindle end a couple of turns. Don't go too tight or it will be to hard to get an end mill inserted. Next, insert the end mill to the proper depth, then tighten the nut against the spindle. Don't go too tight! If the collet it too tight you risk damaging the spindle threads and making it very difficult to remove the nut later.
End mill bits
A roughing operation is used to remove large amounts of material rapidly and to produce a part geometry close to the desired shape. A finishing operation follows roughing and is used to achieve the final geometry and surface finish