BIZOMAT MAKEOS · Manufacturing
Drilling Power, Torque and Thrust
What power, torque and thrust does this drill need?
Spindle speed, feed rate, cutting power, motor power, torque and approximate thrust for a solid twist drill from the specific cutting force.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Drill diameter | mm | Drill diameter. |
| Cutting speed | m/min | Cutting speed at the drill periphery. |
| Feed | mm/rev | Feed per revolution. |
| 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). |
| Point angle | ° | Drill point angle (118° and 140° are common). |
| Machine efficiency | % | Overall machine efficiency from spindle motor to cutting edge (often 70–85%); check the machine manual. |
| Available spindle power | kW | Spindle power at this speed from the machine 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: Drill diameter
- What it is
- The cutting diameter of the twist drill, which is also the diameter of the hole it makes in solid material.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 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 drill lowers spindle speed at the same cutting speed and raises torque and thrust.
- Get it right
- This tool assumes drilling into solid metal; it does not cover opening out an existing hole.
What this means: Cutting speed
- What it is
- The surface speed of the drill’s outer corners, where speed is highest, from the drill supplier’s recommendation.
- Units and format
- Enter a number in m/min: metres per minute. The form accepts 0.000001 m/min to 2000 m/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80 m/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises spindle speed and cutting power in proportion; torque and thrust do not change.
- Get it right
- Enter surface speed, not rpm; the tool calculates rpm from it and the drill diameter.
What this means: Feed
- What it is
- How far the drill advances into the work for each revolution of the spindle.
- Units and format
- Enter a number in mm/rev: millimetres per revolution. The form accepts 0.000001 mm/rev to 5 mm/rev. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.25 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 power, torque and thrust all rise in direct proportion.
- Get it right
- Use feed per revolution for the whole drill, not per cutting lip.
What this means: Specific cutting force kc
- What it is
- The force needed to remove a chip of one square millimetre cross-section in this work material at the drill’s chip thickness, from the tool supplier’s 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 power, torque and thrust rise in direct proportion.
- Get it right
- Use a kc for drilling conditions where available; the chisel edge thrust is not included in this tool.
What this means: Point angle
- What it is
- The included angle between the two cutting lips at the tip of the drill, from the drill catalogue or by measuring the ground point.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 60° to 180°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 118° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger point angle raises the estimated thrust; power and torque do not change.
- Get it right
- This is the full included angle across both lips, not the angle of one lip from the axis.
What this means: Machine efficiency
- What it is
- The share of spindle motor power that reaches the drill point after drive losses, from the machine manual.
- 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.
- Get it right
- Type the percentage itself, not a fraction.
What this means: Available spindle power
- What it is
- The power the drilling spindle can deliver at the calculated spindle speed, from the machine’s power and speed chart.
- 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 7.5 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
- Read the chart at the calculated rpm; small drills run fast, large drills may be below base speed.
Method and formulas
- n = 1000 vc ÷ π D; feed rate = f × n.
- Cutting power Pc = f × vc × D × kc ÷ 240 000 (kW); motor power = Pc ÷ η.
- Torque = Pc × 30 000 ÷ (π n); thrust ≈ 0.5 × kc × (D ÷ 2) × f × sin(point angle ÷ 2).
- Example: a 20 mm drill at 80 m/min and 0.25 mm/rev needs 4.1667 kW and 25 N·m.
Limitations
- The thrust estimate ignores the chisel edge, which can double thrust on drills without point thinning.
- Hole depth, chip evacuation and coolant pressure are not considered.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a large drill against machine power and torque
- Size workholding for drilling thrust
- Compare feed options
Who it is for
- Machinists
- CNC programmers
- Manufacturing engineers
What you get
- Spindle speed and feed rate
- Cutting power and motor power
- Torque
- Approximate thrust force
Interpreting the result
- Clamp the work for the thrust with your safety factor, and support thin parts under the drill.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1089–1093. Topic reference; no source tables or recommended settings are reproduced.
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