Shanks and holders, Does size matter?

Assuming that you have the same size tool (Ex: 1/4 square endmill or whatever) and the tool holder, shank and taper(if applicable) will not interfere with the work. Does the size of the shank or collet holder matter with respect to rigidity and runout??

Examples: ER 16 Vs ER 32 with the exact same tool?? A 1/8" endmill with a 1/8" shank Vs. 1/4" shank??

In a perfect world, assuming the first sentence, would it be better to get the largest holder you can for the tool or the smallest?? Would it be better to get the largest shank you can or the smallest??

How fast do you need to run it. er16 would be better at higher speeds 20 k+
Larger diameter holder the more rotating mass and more critical the balance would be.
If you are choked up near the flutes the shank size probably wont matter. Sticking out the larger shank would be better.
I don’t have anything that runs over 5k so it really doesn’t affect me.


My machine max is 10K, but it’s just a general question to see what people think. I’m new(I didn’t know what an endmill was 10 months ago) and self teaching so I’m soliciting as many opinions as possible, in multiple places, on a lot of what I call “my dumb questions”. Thanks for the input!

Just a suggestion…download GWizard calculator…as a newbie I learned a lot with his programs, including recommended starting speeds and feeds. Within it you could easily play with most of the parameters you’re asking about (Shank size, stickout, etc.) and see what the effect of those changes had on the suggested speed/feed/HP use/tool deflection.

Thank you Sir! I got a 1 year subscription with my mill purchase. It seems to be pretty good, although finicky at times. The speeds and feeds seem to be mostly dead on for a silent cut and a great finish. The only problem I’ve had was the S&F it gave me for working in low carbon steel. I increased the speed and reduced the feed and got it to work eventually though. I quadruple checked everything in fusion and G-wizard and path pilot after the 1st fail and everything looked good, so I still don’t know why it gave me wonky info. I’m 110% sure it’s something I did without realizing it. The only thing I can think of is that the steel was “low carbon” mystery metal from McMaster-Carr, so I bet if I could figure out precisely what it is other than just generic “low carbon”, the S&F from G-wizard would probably be more accurate. Anyway, thank you for the input, I appreciate it!