BIZOMAT MAKEOS · Springs
Ball Detent Check (Spring Preload, Release Force, Spring Stress at Full Rise)
For a spring-loaded ball detent or plunger, what force does it take to push it out of its notch, and is the spring stressed within limits when the ball rides up?
Check of a spring-loaded ball or plunger detent: the spring rate, preload at the fitted length and stress (as the compression spring tool), the force along the sliding direction to push the ball out of a vee notch from the preload, flank angle and friction (as the wedge force tool with the friction on one face), the spring load and stress when the ball has risen out of the notch, and the clearance to solid, against the release force range you want and the allowable stress.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Notch flank angle from the sliding direction | ° | Angle of the notch flank measured from the direction of sliding (45° for a 90° vee). |
| Friction at the ball contact | Friction between the ball and the notch flank. | |
| Ball rise out of the notch | mm | How far the ball moves back into its bore to clear the notch. |
| Least release force wanted | N | Least force that should be needed to move out of the detent position. |
| Largest release force wanted | N | Most force that should be needed. |
| Spring | ||
| Wire diameter | mm | Spring wire diameter. |
| Mean coil diameter | mm | Mean coil diameter. |
| Active coils | coils | Active coils. |
| End type | choice | End type of the spring. |
| Shear modulus | GPa | Shear modulus. |
| Unloaded length | mm | Length of the spring with no load. |
| Fitted length (ball in the notch) | mm | Spring length with the ball seated in the notch. |
| Allowable shear stress | MPa | Allowable shear stress. |
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: Notch flank angle from the sliding direction
- What it is
- The slope of the notch side the ball rides up, measured from the direction the part slides. It sets how much spring force turns into resistance to sliding.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 1° to 80°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 45° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A steeper flank raises the release force.
- Get it right
- Measure from the sliding direction, not from the ball bore axis: the two angles add up to 90°.
What this means: Friction at the ball contact
- What it is
- The friction coefficient where the ball touches the notch flank.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.15 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Higher friction raises the release force.
- Get it right
- Use a value for the actual materials and lubrication; dry hardened steel and greased contacts differ.
What this means: Ball rise out of the notch
- What it is
- How far the ball is pushed back into its bore to climb out of the notch, which compresses the spring further.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Measure along the ball bore axis, from seated in the notch to riding on the flat.
What this means: Least release force wanted
- What it is
- The least sliding force at which the detent should let go, so it holds firmly in normal use.
- Units and format
- Enter a number in N: newtons. The form accepts 0 N to 1000000 N. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15 N as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- It must not exceed the largest release force.
What this means: Largest release force wanted
- What it is
- The largest sliding force the detent may need to release, so it is not too hard to move by hand or drive.
- Units and format
- Enter a number in N: newtons. The form accepts 0.000001 N to 1000000 N. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 N as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Set it from the operating force your design allows.
Spring
What this means: Wire diameter
- What it is
- The diameter of the wire the detent spring is wound from.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Spring rate grows with the fourth power of wire diameter, so small changes move the force a lot.
- Get it right
- Measure the wire with a micrometer; small errors matter.
What this means: Mean coil diameter
- What it is
- The mean diameter of the spring coils, measured to the centre of the wire: outside diameter minus one wire diameter.
- 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 6 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Spring rate falls with the cube of the mean diameter.
- Get it right
- Do not enter the outside diameter; subtract one wire diameter from it.
What this means: Active coils
- What it is
- The number of coils that are free to deflect, excluding closed end coils that sit against each other.
- Units and format
- Enter a number in coils: a number of coils. The form accepts 0.5 coils to 10000 coils. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 coils as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More active coils make a softer spring.
- Get it right
- Count only working coils; total coils include the ends.
What this means: End type
- What it is
- How the spring ends are finished. It sets the number of inactive coils and so the solid length the tool checks at full rise.
- Units and format
- Choose one of 4 options from the list: Closed and ground (squared and ground); Closed, not ground; Plain and ground; Plain (open).
- Example
- The form opens with “Closed and ground (squared and ground)” selected as a worked example. Choose the option that matches your case.
- Get it right
- Check whether the ends are closed (coils touching) and whether they are ground flat.
What this means: Shear modulus
- What it is
- The shear modulus of the spring wire material, which sets the spring rate.
- Units and format
- Enter a number in GPa: gigapascals (1 GPa = 1000 MPa). The form accepts 0.000001 GPa to 500 GPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 79.3 GPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter it in GPa, not MPa; take it from the wire supplier or spring standard.
What this means: Unloaded length
- What it is
- The length of the spring standing free with no load on it.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Measure it before fitting, as springs can set slightly in service.
What this means: Fitted length (ball in the notch)
- What it is
- The length the spring is squeezed to when fitted with the ball seated in the notch. The difference from the free length gives the preload.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 12 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A shorter fitted length raises preload and release force.
- Get it right
- It must not exceed the free length; measure from the bore bottom to the ball seat.
What this means: Allowable shear stress
- What it is
- The highest corrected shear stress you allow in the spring wire, checked at full rise where the spring is shortest.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 100000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 700 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from the wire supplier or a spring design standard for the material and duty.
Method and formulas
- k = G d⁴ ÷ (8 D³ N_a); preload = k (L₀ − L_w); stress with the Wahl factor (as the compression spring tool).
- Release force = preload × tan (α + φ) with tan φ = μ (as the wedge force tool with friction on the ball face only).
- At full rise the spring is at L_w − rise; its load and stress are checked and the length kept above solid.
- Example: 17.209 N preload; 23.283 N to release; 439.11 MPa in the spring at full rise.
Limitations
- Release force at the start of the movement; once the ball rides up, the spring load rises and the angle changes.
- Ball contact on the flank, not the edge, of the notch.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set the holding force of an indexing detent
- Choose a spring for a ball plunger
- Check a detent that slips or is too stiff
Who it is for
- Design engineers
- Toolmakers
- Product designers
What you get
- Spring rate, preload and stress
- Release force
- Spring load and stress at full rise
Interpreting the result
- A steeper notch flank raises the release force far faster than a stiffer spring does.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 304–324, 169–171. Topic reference; no source tables or recommended settings are reproduced.
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Open the Ball Detent Check (Spring Preload, Release Force, Spring Stress at Full Rise) calculator