How to use this calculator
- Enter cut engagement. Enter radial width of cut and axial depth of cut.
- Enter feed and RPM. Use the planned table feed, spindle speed and flute count.
- Enter cutting-force data. Use a specific cutting force for the material/tool condition and a machine efficiency.
- Check power and torque. Compare required spindle power and torque with the machine spindle curve.
How it works
Milling material removal rate is the product of radial engagement, axial depth and programmed feed:
Q = ae x ap x Vf
With kc in N/mm² and Q in
mm³/min, cutting power is:
Pcut(kW) = kc x Q / 60,000,000
Required spindle power divides by the entered efficiency, and spindle torque comes from power and RPM:
Pspindle = Pcut / eta
T = 9550 x Pspindle / n
Worked example
Verified against the live calculator
A cut with 10 mm width, 2 mm depth and
600 mm/min feed removes 12,000 mm³/min, or
12 cm³/min. With kc = 1500 N/mm², cutting power is
0.30 kW. At 80% efficiency the spindle needs
0.375 kW, and at 6000 rpm that is about
0.60 N·m.
Frequently asked questions
How do you calculate milling horsepower?
First calculate material removal rate Q = ae x ap x Vf. Cutting power is approximately kc x Q / 60,000,000 when kc is N/mm² and Q is mm³/min. Required spindle power divides that by machine efficiency.
What is specific cutting force?
Specific cutting force kc is a material and cutting-condition coefficient. It changes with material, tool geometry, chip thickness, coating, wear and coolant, so use a toolmaker value when available.
How is spindle torque calculated?
Torque comes from power and RPM: T = 9550 x P(kW) / RPM. Low RPM cuts can require high torque even when horsepower is modest.
Is this the same as a feeds and speeds calculator?
No. This checks MRR, spindle power and torque after you have a feed and cut engagement. Use the CNC speeds and feeds calculator first to choose RPM and feed.
Method & assumptions
- Uses rectangular engagement: material removal rate = width of cut x depth of cut x feed rate.
- Specific cutting force is user-entered. Toolmaker data or machine load observations are better than generic values.
- Does not model entry/exit angle, radial chip thinning, interrupted cuts, tool wear, chatter, coolant, machine acceleration or spindle power curve limits.
- Use CNC speeds and feeds and chip load before checking power, then send cycle time to the machining time calculator.