Back in HSS days endmill shanks were rarely below 3/8" no matter the cutter diameter. With carbide endmills the shank diameter are usually the same as the cutter diameter (until you get to 1/8" or 1mm). We were curious, what would be the impact if you used a larger shank with a smaller cutter diameter. In figure 1, we used RCSA to model three different tool designs of a 3/8" endmill. You can see the results for yourself. This was not a definitive study, just an exercise because we were curious.
In figure 2, the change is subtle, using a 5/8" shank instead of a 1/2". In this one example (again, not a definitive study), the larger shank produced a higher speed lobe and significantly greater metal removal rate.
Our takeaway is if you are concerned with metal removal rate or having stability issues, perhaps a larger shank will help.
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