BIZOMAT MAKEOS · Manufacturing
Turning Cutting Force and Power
What cutting force, power and torque does this turning cut need, and can the machine deliver it?
Cutting force, cutting power, spindle motor power, torque and metal removal rate for a turning cut from specific cutting force, compared with the available machine power.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Cutting speed | m/min | Cutting speed from the tooling recommendation. |
| Feed | mm/rev | Feed per revolution. |
| Depth of cut | mm | Radial depth of cut. |
| Workpiece diameter | mm | Workpiece diameter at the cut. |
| Specific cutting force kc | N/mm² | Specific cutting force for the work material at your chip thickness, from the tool supplier’s data (e.g. about 1500–2100 N/mm² for steels, 500–800 N/mm² for aluminium alloys). |
| Machine efficiency | % | Overall machine efficiency from spindle motor to cutting edge (often 70–85%); check the machine manual. |
| Available spindle power | kW | Rated spindle power at the speed you will run, from the machine power–speed chart. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Cutting speed
- What it is
- The surface speed of the workpiece past the cutting edge, measured at the diameter being cut. It usually comes from the insert supplier’s recommendation for the grade and work material.
- Units and format
- Enter a number in m/min: metres per minute. The form accepts 0.000001 m/min to 5000 m/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 m/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Cutting power and removal rate rise in direct proportion; cutting force does not change.
- Get it right
- This is surface speed in metres per minute, not spindle rpm; the tool works out rpm from it and the diameter.
What this means: Feed
- What it is
- How far the tool advances along the work for each turn of the spindle, as programmed or set on the lathe feed box.
- Units and format
- Enter a number in mm/rev: millimetres per revolution. The form accepts 0.000001 mm/rev to 10 mm/rev. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.3 mm/rev as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Cutting force, power and removal rate all rise in direct proportion.
- Get it right
- Use feed per revolution; if your program gives mm/min, divide by the spindle rpm first.
What this means: Depth of cut
- What it is
- How deep the tool cuts into the work on one side, measured radially from the uncut surface to the cut surface.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Cutting force, power and removal rate all rise in direct proportion.
- Get it right
- Depth of cut is per side: reducing the diameter by 6 mm is a 3 mm depth of cut.
What this means: Workpiece diameter
- What it is
- The diameter of the workpiece where the tool is cutting. The tool uses it for spindle speed and for the torque the force creates at that radius.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger diameter lowers spindle speed and raises torque; force and power do not change.
- Get it right
- Use the diameter at the cut, not the bar stock size if the part has already been reduced.
What this means: Specific cutting force kc
- What it is
- The force needed to cut a chip of one square millimetre cross-section in this work material. It depends on the material, the chip thickness and the tool geometry, and comes from the tool supplier’s cutting data.
- Units and format
- Enter a number in N/mm²: newtons per square millimetre (equal to MPa). The form accepts 0.000001 N/mm² to 10000 N/mm². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2000 N/mm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Cutting force and power rise in direct proportion.
- Get it right
- Pick the kc for your actual chip thickness; thin chips need a higher kc, and a worn tool raises the real value.
What this means: Machine efficiency
- What it is
- The share of the spindle motor’s electrical power that actually reaches the cutting edge after losses in belts, gears and bearings, from the machine manual or maker.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 1% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A lower efficiency raises the motor power required; cutting power does not change.
- Get it right
- Type the percentage itself, not a fraction.
What this means: Available spindle power
- What it is
- The power the spindle motor can deliver at the speed this cut runs, read from the machine’s power and speed chart rather than the nameplate maximum.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0.000001 kW to 10000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only moves the pass or fail line; the power required does not change.
- Get it right
- Many lathes give full power only above a base speed; check the chart at the calculated rpm.
Method and formulas
- Cutting force Fc = kc × ap × f.
- Cutting power Pc = Fc × vc ÷ 60 000 (kW); motor power = Pc ÷ η.
- Spindle speed n = 1000 vc ÷ πD; torque = Fc × D ÷ 2000 (N·m).
- Removal rate Q = vc × ap × f (cm³/min).
- Example: 3 mm × 0.3 mm/rev at 200 m/min in kc 2000 steel needs 7.5 kW at the motor.
Limitations
- kc depends on chip thickness, rake angle and tool wear; a worn tool can raise force by 30% or more.
- Power available falls at low spindle speeds on most machines; use the power–speed curve.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a roughing cut against machine power
- Find the depth of cut a lathe can take
- Estimate spindle torque at low speed
Who it is for
- Machinists
- CNC programmers
- Manufacturing engineers
What you get
- Cutting force
- Cutting power and motor power
- Spindle speed and torque
- Metal removal rate
Interpreting the result
- Keep a margin below the available power for tool wear and hard spots.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1084–1101. Topic reference; no source tables or recommended settings are reproduced.
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