KEVOS® 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. |
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
