KEVOS® MAKEOS · Manufacturing
Trepanning Plan (Ring Cut Power, Torque, Time and Core against Solid Drilling)
Should a large hole be trepanned or drilled solid: what power, torque and time does each need, how much metal does trepanning leave as a usable core, and can the machine do it?
Plan for cutting a large hole by trepanning, which removes only a ring and leaves a solid core, compared with drilling it solid: the spindle speed, the cutting power and torque for the ring from the kerf width, feed, mean cutting speed and specific cutting force, the motor power against the spindle power, the cutting time, the volume removed and the core diameter, mass and value, and the same speed and power for a solid drill of the hole size (as the drilling cycle planner tool).
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Hole | ||
| Hole diameter | mm | Diameter of the hole to be made. |
| Hole depth | mm | Depth of the hole (the length of the core for a through hole). |
| Trepanning kerf width (radial) | mm | Radial width of the groove the trepanning tool cuts, from the tool maker; the core diameter is the hole diameter less twice this. |
| Approach and breakthrough clearance | mm | Extra travel before and after the cut. |
| Cut | ||
| Cutting speed at the hole diameter | m/min | Cutting speed at the outside of the hole for the tool material and work, from the tool maker or cutting data. |
| Trepanning feed per revolution | mm/rev | Feed per revolution for the trepanning tool. |
| Solid drilling feed per revolution | mm/rev | Feed per revolution a solid drill of this size would use, for the comparison. |
| Solid drill point angle | ° | Point angle of the solid drill, for its travel. |
| Specific cutting force | N/mm² | Specific cutting force for the work material at this chip thickness, from the tool maker or a cutting data handbook. |
| Machine efficiency | % | Share of motor power that reaches the spindle. |
| Spindle power available | kW | Spindle (motor) power the machine can deliver at this speed. |
| Core | ||
| Work material density | kg/m³ | Density of the work material (steel about 7,850 kg/m³). |
| Value of the recovered core | A$/kg | What the core is worth: its value as bar stock or scrap, per kilogram. |
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.
Hole
What this means: Hole diameter
- What it is
- The finished diameter of the large hole, which is the outside diameter of the ring the trepanning tool cuts.
- 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 60 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 spindle speed and, with the kerf, the core size; solid drilling power rises in proportion.
- Get it right
- Trepanning suits holes from about 50 mm upwards; below that, a solid drill is usually simpler.
What this means: Hole depth
- What it is
- The depth of the hole, which for a through hole is also the length of the core that comes out.
- 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 150 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Time, volume removed and core mass rise in proportion.
- Get it right
- Use the full material thickness for a through hole.
What this means: Trepanning kerf width (radial)
- What it is
- The radial width of the groove the trepanning tool cuts, the only part of the hole turned into chips.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 200 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 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 in proportion; a wider kerf leaves a smaller core.
- Get it right
- Take it from the trepanning head or insert maker; narrow kerfs need less power but are harder to clear of chips.
What this means: Approach and breakthrough clearance
- What it is
- The extra travel before the tool reaches the work and after it breaks through, cut at feed rate.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 200 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
- Adds to the cutting time of both methods.
- Get it right
- A few millimetres is usual; more if the surface is uneven.
Cut
What this means: Cutting speed at the hole diameter
- What it is
- The surface speed of the cutting edge at the outside of the hole, which sets the spindle speed.
- 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 both powers and shortens both times in proportion.
- Get it right
- Take it from the tool maker for the insert grade and work material; the same speed is used for the solid drill comparison.
What this means: Trepanning feed per revolution
- What it is
- How far the trepanning tool advances along the hole for each revolution, which with the kerf width sets the chip area.
- 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 0.12 mm/rev as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Trepanning power rises and time falls in proportion.
- Get it right
- Use the tool maker’s feed; trepanning feeds are usually lighter than solid drill feeds.
What this means: Solid drilling feed per revolution
- What it is
- The feed per revolution a solid drill of this diameter would use, for comparing its power and time with trepanning.
- 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
- Changes only the solid drilling comparison.
- Get it right
- Use the drill maker’s feed for this size and material.
What this means: Solid drill point angle
- What it is
- The point angle of the solid drill in the comparison, which sets how far its point travels past the depth.
- 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 smaller angle lengthens the solid drill’s travel slightly.
- Get it right
- 118° is common on general-purpose drills; large indexable drills are often flatter.
What this means: Specific cutting force
- What it is
- The specific cutting force of the work material: the cutting force per square millimetre of chip cross-section.
- 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
- Both powers and the torque rise in proportion.
- Get it right
- Take it from the tool maker’s data for the material group and chip thickness.
What this means: Machine efficiency
- What it is
- The share of the motor’s power that reaches the spindle after losses in belts, gears and bearings.
- 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 needed.
- Get it right
- About 75 to 90 % is usual; use the machine maker’s figure if known.
What this means: Spindle power available
- What it is
- The power the machine’s spindle drive can deliver at the speed used, checked against the motor power each method needs.
- 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 11 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 line.
- Get it right
- Read the spindle power curve at this speed; many spindles give less than their rated power at low speed.
Core
What this means: Work material density
- What it is
- The density of the work material, used to turn the core volume into a mass.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 100 kg/m³ to 25000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7850 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Core mass and value rise in proportion.
- Get it right
- Steel is about 7,850 kg/m³, aluminium about 2,700 kg/m³.
What this means: Value of the recovered core
- What it is
- What the solid core left by trepanning is worth per kilogram, as usable bar stock or as clean scrap.
- Units and format
- Enter a number in A$/kg: A$/kg. The form accepts 0 A$/kg to 100000 A$/kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.5 A$/kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Core value rises in proportion.
- Get it right
- Use the scrap price if the core will not be reused; enter 0 to ignore its value.
Method and formulas
- Spindle speed n = 1000 v_c ÷ (π D); mean cutting speed of the ring v_m = v_c (D − w) ÷ D.
- Trepanning cutting power P = k_c w f v_m ÷ 60,000 kW; motor power P ÷ η; torque = P × 30,000 ÷ (π n) N·m; time = (depth + clearance) ÷ (n f).
- Core diameter D_c = D − 2w; volume removed = π ÷ 4 (D² − D_c²) L; core mass = ρ π D_c² L ÷ 4.
- Solid drill (as the drilling cycle planner tool): P = f_D v_c D k_c ÷ 240,000 kW, time = (depth + point length + clearance) ÷ (n f_D).
- Example: trepanning a 60 mm hole needs 2.16 kW at the motor and 3.0041 min, leaving a 48 mm core of 2.1308 kg; a solid drill needs 12.5 kW.
Limitations
- Unit-power estimate of the cutting power; feed force, chip evacuation and the stiffness of the long tool are not checked.
- The solid drill is taken at the same cutting speed; large drills often run slower, so check its own data.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Decide between trepanning and solid drilling for a large hole
- Check that the machine has the power for the cut
- Value the core trepanning leaves
Who it is for
- Machinists
- Process planners
- Manufacturing engineers
What you get
- Spindle speed and mean cutting speed
- Trepanning power, motor power, torque and time
- Volume removed, core diameter, mass and value
- Solid drilling power and time for comparison
Interpreting the result
- Trepanning removes only the ring, so it needs a fraction of the power of solid drilling and leaves a core worth keeping; it is often the only way to make a large, deep hole on a machine of modest power.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1077–1081, 1084–1092. 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.
Open the Trepanning Plan (Ring Cut Power, Torque, Time and Core against Solid Drilling) calculator