How to use the cutting force and spindle power calculator
When you push cutting conditions, the first limit you hit is usually the machine spindle rather than the insert. Working out required power ahead of time keeps the conditions inside what the machine can actually deliver, and knowing the cutting force also tells you whether the workholding, the part deflection and the toolholder stiffness will cope.
Power is calculated from unit power and metal removal rate: hp = Up × MRR, with MRR = 12 × SFM × feed × depth of cut in in³/min. Unit power falls as the chip gets thicker, so it is corrected with Up = Up0.010 × (feed ÷ 0.010)−mc. Tangential force follows from Fc = 33,000 × hp ÷ SFM. The values listed are at the cutter; figures quoted at the motor are higher because they already include drive efficiency.
Unit power values here are representative of each material group and shift with hardness, heat treatment, tool rake angle and wear. A worn insert can raise cutting force by 20 to 50 %, so leave margin when you check spindle power against the machine rating. This calculator is set up for outside diameter turning.
Frequently asked questions
A thicker chip needs less energy per unit volume removed. For the same removal rate, taking a deeper, heavier cut is therefore more power-efficient than a light, fast one.
Power based on removal rate is broadly comparable, but milling teeth cut intermittently and the average chip thickness differs. Treat this tool as a turning calculation and size milling cuts with a milling-specific method.