the Endmill will tend to pull itself out of the collet, especially light duty collets like are on a router...CNC machine tools use havvy duty collets that have much more clamping ability...but they stiill can pull out...so most of the time it is a good idea to use a set screw tool holder or a collet wit han indexing lug...I do realize this may not be possible on a CNC router tho..
