BIZOMAT MAKEOS · Manufacturing
Spade Drilling Power and Thrust
What power and thrust does this spade drilling operation need?
Power at the cutter and at the motor, and the thrust force, for spade drilling by the handbook formulas from drill diameter, feed, speed and the unit power of the work material, with an allowance for tool wear.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Drill diameter | mm | Diameter of the spade drill. |
| Feed per revolution | mm/rev | Feed per revolution. |
| Spindle speed | rpm | Spindle speed. |
| Unit power of the material | kW per cm³/min | Unit power for spade drilling the work material (from tooling or handbook data for the material and hardness). |
| Machine mechanical efficiency | Mechanical efficiency of the machine drive (about 0.9 belt direct drive, 0.75 back gear, 0.7–0.8 geared head). | |
| Allowance for tool wear | % | Increase for a dulling tool (the handbook suggests 25–50% for a dull tool). |
| Motor power available | kW | Rated motor power of the machine. |
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 diameter of the spade drill blade, which is the diameter of the hole it cuts.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 300 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Power rises with the square of the diameter; thrust rises in direct proportion to it.
What this means: Feed per revolution
- What it is
- How far the drill advances along its axis in one spindle revolution.
- 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 0.3 mm/rev as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Power and thrust both rise in direct proportion to the feed.
- Get it right
- Per revolution, not per cutting lip and not per minute.
What this means: Spindle speed
- What it is
- The speed of the spindle turning the drill while it cuts.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 100000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Power rises in proportion to speed; thrust does not depend on it.
- Get it right
- Spindle rpm, not cutting speed in m/min; convert with n = 1000 V ÷ (π D).
What this means: Unit power of the material
- What it is
- The power needed to remove one cubic centimetre of the work material per minute by spade drilling. It depends on the material and its hardness.
- Units and format
- Enter a number in kW per cm³/min: kW per cm³/min. The form accepts 0.000001 kW per cm³/min to 1 kW per cm³/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.0359 kW per cm³/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Power and thrust are both directly proportional to the unit power.
- Get it right
- Take it from tooling or handbook data for the material and hardness; data in hp per in³/min must first be converted to kW per cm³/min.
What this means: Machine mechanical efficiency
- What it is
- The share of motor power that reaches the spindle after losses in belts, gears and bearings, written as a decimal fraction.
- Units and format
- Enter a plain number with no unit. The form accepts 0.3 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.8 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Motor power is cutter power divided by this efficiency, so a lower value needs more motor power.
- Get it right
- Type a fraction (0.85 for 85 %), not a percentage.
What this means: Allowance for tool wear
- What it is
- The extra power and thrust allowed for the drill losing its edge during the cut, added as a percentage to the sharp-tool values.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Power and thrust are both multiplied by (1 + allowance ÷ 100).
- Get it right
- Enter 0 for sharp-tool values; the allowance applies to both power and thrust.
What this means: Motor power available
- What it is
- The rated power of the machine’s spindle motor, which the motor power needed is compared with.
- 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
- It does not change the power needed; it sets the utilisation and the pass or fail verdict.
- Get it right
- If the maker states a lower power for the speed range you use, enter that instead of the nameplate rating.
Method and formulas
- Power at the cutter kW_c = ukw × (π D² ÷ 4) × f × N ÷ 1000.
- Thrust B_s = 22,500 × ukw × f × D newtons (US form 148,500 uhp f D pounds).
- Motor power = kW_c ÷ e_m; wear allowance applied to both power and thrust.
- Example: a 40 mm spade drill at 0.3 mm/rev and 300 rpm needs 6.3441 kW at the motor.
Limitations
- Values for sharp tools; dull tools raise power and thrust 25–50%.
- Unit power varies with hardness and tool geometry.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check whether a machine can drive a large spade drill
- Size fixturing against drilling thrust
- Compare feeds for power and thrust
Who it is for
- Machinists
- Toolmakers
- Manufacturing engineers
What you get
- Power at the cutter and motor
- Thrust force
- Machine utilisation
Interpreting the result
- Reduce feed before speed if thrust is the limit; reduce speed if power is.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1077–1079. Topic reference; no source tables or recommended settings are reproduced.
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