"You can't get there from here"
Let's take a 1/4" endmill in a 10,000 RPM machining center. The endmill's recommended surface speed is 2000 SFM. To reach that you would have to run the tool at 30,558 RPM (SFM x (12/π)/Diameter = RPM). Because the largest and deepest stability lobes are at the fastest speeds, with only 10K RPM you are not going to get there. Endmills smaller than 1/4" and the lack of speed capacity gets magnified. At lower speeds, the cutting action of the endmill is compromised. A spindle speeder like the Colibri Spindles or an air spindle are a solution. It also makes me wonder if going back in time and using small cobalt endmills might be a forgiving alternative.
Another limiting issue is cost. Small carbide endmills are inexpensive. For example a ¼” endmill from one manufacturer sells online for $22.50, their ½” is $60.73 and their ¾” is $218.84. It it tough justify a lot of effort that yields little cost avoidance. Break and replace becomes a strategy.
Small endmills are VERY flexible (until they break) so very susceptible to forced (runout, unbalance) and self-excited vibration (dynamics).
In the next post, we will (finally) offer some suggestions to improve small endmill performance.
Sharing information about high performance milling technologies, the result of 30 years of research.