In the beginning there were end mill holders.  They might have been on a   v- flange (cat 40 or 50 taper) or R-8 holder,  but they simply had a hole in the end with a set screw on the side to lock down on the end mill.  While this was ok for high Speed end mills, it was detrimental to carbide end mills. 

Then came the “DA” collet holder.  It was a little better but was used mainly for drilling and reaming.  The side wall of the holder was too thin for heavy side loads generated in milling applications.

Now that high speed milling is all the rage,  there are better ways to hold carbide end mills.  ER collet chucks, TG collet chucks, Milling chucks, hydraulic holders, heat shrink, and 3 point contact holders are some of the more common ways.

At first Carbide end mill manufacturers did not put weldon flats on carbide end mills because they wanted them held accurately, and that was not accomplished thru the use of an end mill holder.  The problem with end mill holders is they “push”, the cutter slightly off center so that one of the flutes takes more of a cut than the other flutes.  This results in a high degree of corner chipping.

With any of the other type holders, they tend to hold the cutters on center so that the flutes are running concentric with the spindle of the machine.

Holding power aside, the concentricity of a carbide end mill needs to be true.  TIR is very important with these tools.  Therefore the ER, TG, Straight, shrink and 3 point  holders are best way to hold the carbide end mills.

When it comes to solid carbide end milling,  a sharp corner on the end of the cutting tool is usually the first thing to chip or break off.  It’s like when you were a child in grammar school and you always wanted a sharp pencil point to start with when writing a new paper.  When the point was new, it was fragile and therefore you learned to be gentile with it.  Then as the writing progressed, the point would become dull ( or rounded) on the end.  This actually made the pencil stronger and you became less gentile and more “bearing” on the point.

The same principle is applied with a solid carbide end mill.  If we start the tool with a corner radius, even one as small as .010″ ,  the edge strength ( or corner) becomes stronger.  The larger the radius the stronger the corner.  This makes the end mill last longer and give more rigidity to the cutting edge.

While some part prints call for sharp corners on a part,  a majority of the work can usually be done first with a tool that has some radius on it.  Then switching to a sharp corner tool to finish the part.