How to use this calculator
- Enter work diameter and speed. Use the work diameter at the cutting edge and the planned surface speed.
- Enter feed and depth. Use feed per revolution and radial depth of cut for the turning pass.
- Enter kc and efficiency. Use a specific cutting force for the material/tool condition and a machine efficiency allowance.
- Check spindle load. Compare required power and torque with the spindle curve and machine load meter.
How it works
Turning starts by converting surface speed and work diameter into spindle RPM:
n = Vc x 1000 / (pi x D)
The uncut chip area is feed per revolution times radial depth of cut. Material removal rate follows from that chip area and cutting speed:
A_c = fn x ap
Q = Vc x 1000 x fn x ap
With kc in N/mm^2 and Q in
mm^3/min, cutting power is:
Pcut(kW) = kc x Q / 60,000,000
Pspindle = Pcut / eta
T = 9550 x Pspindle / n
Worked example
Verified against the live calculator
A 50 mm work diameter at 180 m/min gives about
1146 rpm. With 0.20 mm/rev feed and a
2 mm radial depth of cut, MRR is 72 cm^3/min.
At kc = 1500 N/mm^2, cutting power is 1.8 kW;
with 80% efficiency, required spindle power is
2.25 kW.
Frequently asked questions
How do you calculate turning horsepower?
For turning, material removal rate is cutting speed times feed per revolution times depth of cut. Cutting power is estimated from specific cutting force and MRR, then divided by machine efficiency to get required spindle power.
How is turning RPM calculated from cutting speed?
RPM = Vc x 1000 / (pi x D) when Vc is in m/min and diameter is in mm. In imperial units this is the same SFM-to-RPM relation used by the surface speed calculator.
What is specific cutting force?
Specific cutting force kc is a material and tool-condition coefficient. It changes with insert geometry, chip thickness, lead angle, wear, coating and coolant, so toolmaker data is better than a generic value.
Is this a feeds and speeds calculator?
No. This checks spindle load after you choose a turning speed, feed and depth of cut. Use the cutting-speed and surface-finish calculators for adjacent setup checks.
Method & assumptions
- Uses orthogonal turning MRR: cutting speed x feed per revolution x depth of cut.
- Specific cutting force is user-entered; use insert/toolmaker data or observed machine load when possible.
- Does not model lead angle chip thinning, interrupted cuts, tool wear, work hardening, chatter, coolant, acceleration or spindle power-curve limits.
- Use surface feet per minute, cutting speed, turning surface finish and machining time for adjacent checks.