Ball End mill speeds Practical Machinist
Dec 29, 2009· I took a series of machining classes at a community college in CA years ago. The simple guidance given for cutting steel with HSS was 100sfm at the largest diameter. Approximating pi allows the simple formula of 4 x cutting speed (sfm) / diameter (inches). For form cutters like your ball endmill, the recommendation was to cut that rpm in half.