KEVOS® MAKEOS · Manufacturing
Taper Shank Holding Check (Drilling Torque, Thrust, Taper Friction Torque, Self-Holding)
When a taper-shank drill cuts, can the friction in the taper alone carry the drilling torque, or does the tool need its tang or a drawbar, and is the taper self-holding?
Check of a taper-shank tool in its socket while drilling: the spindle speed, cutting power, torque and approximate thrust of the drill (as the drilling cycle planner tool), the normal force the thrust develops on a taper of the given rate, the friction torque the taper can carry from it at the mean engaged diameter, the ratio of that capacity to the drilling torque against your safety factor, and whether the taper angle is small enough to be self-holding for the friction coefficient you enter.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Drill and cut | ||
| Drill diameter | mm | Diameter of the drill. |
| Cutting speed | m/min | Cutting speed for this drill and material, from the tool maker or cutting data. |
| Feed per revolution | mm/rev | Feed per revolution. |
| Specific cutting force | N/mm² | Specific cutting force for the work material, from the tool maker or a cutting data handbook. |
| Point angle | ° | Point angle of the drill. |
| Taper | ||
| Large diameter of the taper at the gauge line | mm | Diameter of the taper at its large end where it engages the socket, from the taper standard or the tool drawing. |
| Taper on diameter per unit length | Taper rate: change in diameter per unit length (Morse tapers are close to 1 in 20, about 0.05; steep spindle tapers are much larger). | |
| Engaged length of the taper | mm | Length of taper actually in contact with the socket. |
| Friction coefficient in the taper | Coefficient of friction between clean, dry steel taper surfaces; oil or dirt lowers it sharply. Use a cautious value. | |
| Required ratio of taper capacity to drilling torque | Margin you require between the taper's friction torque and the drilling torque. | |
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.
Drill and cut
What this means: Drill diameter
- What it is
- The diameter of the taper-shank drill, which with the feed and cutting force sets the torque and thrust it puts on its socket.
- 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 20 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Torque rises roughly with the square of the diameter, thrust in proportion to it.
- Get it right
- Use the drill’s nominal size.
What this means: Cutting speed
- What it is
- The surface speed at the outside of the drill, which with the diameter sets the spindle speed and the cutting power.
- Units and format
- Enter a number in m/min: metres per minute. The form accepts 0.000001 m/min to 1000 m/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25 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 the power and spindle speed but not the torque, which depends on the chip load.
- Get it right
- Take it from the drill maker for the drill type and work material.
What this means: Feed per revolution
- What it is
- How far the drill advances for each revolution of the spindle, which with the diameter sets the chip load and so the torque and thrust.
- 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
- Torque and thrust rise in proportion, so their ratio, and the holding margin, stay much the same.
- Get it right
- Use the programmed feed; a heavier feed raises the thrust that seats the taper as well as the torque.
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
- Torque and thrust rise in proportion.
- Get it right
- Take it from the tool maker’s data for the material group.
What this means: Point angle
- What it is
- The included angle of the drill point, which affects how much of the cutting force acts along the axis as thrust.
- 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 thrust in this estimate and so the holding torque.
- Get it right
- 118° is common on general-purpose drills.
Taper
What this means: Large diameter of the taper at the gauge line
- What it is
- The diameter of the tool’s taper at its large end where it seats in the socket, the gauge-line diameter of the taper size.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 500 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 24 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 taper gives a larger mean diameter and more holding torque.
- Get it right
- Take it from the taper standard for the taper number, or measure the shank.
What this means: Taper on diameter per unit length
- What it is
- The taper rate: how much the diameter changes per unit of length along the shank, which sets the taper’s half-angle.
- Units and format
- Enter a plain number with no unit. The form accepts 0.0001 to 2. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.05 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A gentler taper multiplies the thrust into a larger normal force and more holding torque.
- Get it right
- Morse tapers are close to 1 in 20 on diameter (about 0.05); steep self-releasing spindle tapers are several times larger.
What this means: Engaged length of the taper
- What it is
- The length of the taper actually in contact with the socket, used to find the mean diameter of the contact.
- 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 75 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A longer engagement lowers the mean diameter slightly in this model.
- Get it right
- Use the length of the shank that seats in the socket, less any length of a worn or damaged mouth that does not touch.
What this means: Friction coefficient in the taper
- What it is
- The coefficient of friction between the shank and the socket, which turns the normal force into resistance to turning and decides whether the taper is self-holding.
- Units and format
- Enter a plain number with no unit. The form accepts 0.01 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Holding torque rises in proportion; the taper is self-holding only while tan α is below it.
- Get it right
- Clean, dry steel tapers grip far better than oily or dirty ones; use a cautious value and clean both tapers before fitting.
What this means: Required ratio of taper capacity to drilling to…
- What it is
- The margin you require between the friction torque the taper can carry and the torque the drill needs, to allow for variation in friction and cutting force.
- Units and format
- Enter a plain number with no unit. The form accepts 0.1 to 20. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 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
- Choose it from your own practice; a dull drill can need much more torque than a sharp one.
Method and formulas
- Drilling (as the drilling cycle planner tool): n = 1000 v_c ÷ (π D); P_c = f v_c D k_c ÷ 240,000 kW; torque = P_c × 30,000 ÷ (π n) N·m; thrust ≈ 0.5 k_c (D ÷ 2) f sin(point ÷ 2).
- Taper half-angle α = atan(c ÷ 2); mean engaged diameter D_m = D_l − c L_e ÷ 2.
- Normal force from the thrust while seating: N = F_a ÷ (sin α + μ cos α); friction torque capacity T = μ N D_m ÷ 2.
- Self-holding when tan α < μ: the taper then stays seated without thrust; otherwise it is self-releasing and needs a drawbar.
- Example: the drill needs 25 N·m; 2,142.9 N of thrust lets the taper carry 18.971 N·m, a ratio of 0.75883.
Limitations
- Friction depends heavily on cleanliness and lubrication; the result is an estimate of the order of the holding torque, not a rating.
- Uses the cutting thrust as the only seating force and treats the taper as fully in contact; a worn or damaged socket contacts only in places.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check whether a taper-shank drill will slip in its socket
- Decide whether a tang or drawbar is needed
- Compare a self-holding taper with a steep self-releasing one
Who it is for
- Machinists
- Tooling engineers
- Manufacturing engineers
What you get
- Spindle speed, cutting power, drilling torque and thrust
- Taper half-angle and mean engaged diameter
- Normal force and friction torque capacity of the taper
- Capacity ratio and whether the taper is self-holding
Interpreting the result
- A self-holding taper grips because its angle is small, but the torque it carries still depends on the thrust pushing it in; a large drill at a light feed can spin in its socket, which is what the tang is there to prevent.
- Never rely on a tang to drive in normal cutting: a tang that is doing the work shows the taper is dirty, damaged or too lightly seated.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 948–959, 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.
Explains the concept · Library collection
Workholding and toolholding: vices, chucks, zero-point systems, tapers and holders
What it covers: How standard workholding and toolholding choices affect accuracy, tool life, set-up time and safety, from vices and chucks to zero-point pallets, spindle tapers, collets and shrink-fit holders.
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.