KEVOS® MAKEOS · Manufacturing
Grinding Force, Torque and Power from Equivalent Chip Thickness
For my equivalent chip thickness, width of cut and specific grinding force, what tangential and normal grinding forces act on the wheel, and what torque and power does the wheel spindle need?
Grinding forces as the handbook works them: chip area = ECT × CEL, tangential force Fc = Kc × ECT × CEL with the specific grinding force Kc you enter (around 30 to 40 times the turning values), normal force FH = (FH ÷ FC) × Fc with the force ratio you enter (generally 2 to 4), and the wheel torque Fc × D ÷ 2 and power Fc × V ÷ 60,000, compared with the spindle power available.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Equivalent chip thickness ECT | mm | Equivalent chip thickness of the grinding cut. |
| Cutting edge length (width of cut) CEL | mm | Length of the cutting edge in contact, the width of cut. |
| Specific grinding force Kc | N/mm² | Specific grinding force for the work material and ECT, from data or tests. |
| Normal to tangential force ratio FH ÷ FC | Ratio of the normal to the tangential grinding force, from data or tests. | |
| Wheel speed V | m/min | Peripheral speed of the wheel. |
| Wheel diameter | mm | Diameter of the grinding wheel. |
| Spindle power available (0 = no check) | kW | Power available at the wheel spindle, if you want it checked. |
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: Equivalent chip thickness ECT
- What it is
- Average chip thickness along the cutting edge, the equivalent chip thickness.
- Units and format
- Enter a number in mm: millimetres. The form accepts 1e-7 mm to 0.1 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.00017 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The forces rise in proportion.
- Get it right
- In grinding it is about the work speed times the depth of cut divided by the wheel speed.
What this means: Cutting edge length (width of cut) CEL
- What it is
- Length of the wheel edge in contact with the work, the width of cut.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The forces rise in proportion.
- Get it right
- Use the contact width of the wheel face on the work.
What this means: Specific grinding force Kc
- What it is
- Force per unit chip area for this work material and wheel at your ECT.
- Units and format
- Enter a number in N/mm²: newtons per square millimetre (equal to MPa). The form accepts 0.000001 N/mm² to 1000000 N/mm². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150000 N/mm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The tangential force rises in proportion.
- Get it right
- Take it from grinding force data or a test; it is far higher than in turning.
What this means: Normal to tangential force ratio FH ÷ FC
- What it is
- How many times larger the normal force is than the tangential force.
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 to 20. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2.5 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the normal force on the work.
- Get it right
- Take it from grinding data or a test; the handbook gives about 2 to 4.
What this means: Wheel speed V
- What it is
- Peripheral speed of the grinding wheel surface.
- Units and format
- Enter a number in m/min: metres per minute. The form accepts 0.000001 m/min to 20000 m/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2000 m/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The power rises in proportion.
- Get it right
- V = π D n ÷ 1000 with D in mm and n in rpm.
What this means: Wheel diameter
- What it is
- Outside diameter of the grinding wheel at present.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 3000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the torque at the wheel spindle.
- Get it right
- Use the current diameter; it shrinks as the wheel is dressed.
What this means: Spindle power available (0 = no check)
- What it is
- Power the wheel spindle can deliver to the cut.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0 kW to 1000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Compared with the power the cut needs.
- Get it right
- Use the motor rating times the drive efficiency, or 0 to skip the check.
Method and formulas
- Chip area = ECT × CEL.
- Tangential force Fc = Kc × chip area; normal force FH = (FH ÷ FC) × Fc.
- Torque = Fc × D ÷ 2; power = Fc × V ÷ 60,000 kW (V in m/min).
- Example: the tangential force is 255 N and the wheel needs 8.5 kW.
Limitations
- Kc and the force ratio depend on the work material, wheel, ECT and speed; enter values from data or tests.
- The power is at the wheel; allow for the drive losses of the machine.
- Forces rise as the wheel dulls; use values for a worn wheel when sizing the machine.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check the spindle power for a grinding cut
- Estimate the normal force on the work and fixture
- Compare grinding forces at different ECT
Who it is for
- Manufacturing engineers
- Grinding machinists
- Fixture designers
What you get
- Chip area
- Tangential and normal grinding forces
- Wheel torque and power
- Whether the spindle power is enough
Interpreting the result
- Kc for grinding is much higher than for turning because the ECT is very small and the grits cut with large negative rake.
- The normal force is the larger one and sets the deflection of the work and the spark-out time.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1203–1204. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These KEVOS® Library readings explain the method this tool uses, with worked examples.
Useful alongside · KEVOS® original book
Cutting force, power and torque
What it covers: Estimate specific cutting force from chip thickness, calculate cutting force, power and spindle torque, and check planned cuts against a machine's power and torque curve.
KEVOS® tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
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