Design Guidelines for Ball Plungers

In order to calculate the side force, Fs, necessary to disengage a ball plunger from the detent hole you need to know the end force of the ball, FE, the resultant force, FR and the countersink angle. See the diagram below for reference. Since FR is perpendicular to the contact surface, use the following equation to solve for FS:


Starting and final end forces for each ball plunger are given in the ball plunger tables. Typically the midpoint of these values is used in solving the above equation.

Calculation Example

bp_diagramFor P/N SW10-5B the starting and final end forces are 4 and 9 lbs, respectively, so we would use a midpoint value of 6.5. If the countersink angle is 90°, the equation is solved as follows:

FE = 6.5 lb
0 = 90°
FS = 6.5 / tan (90°/2) = 6.5 lb

In this example it will take a side force of 6.5 lbs to disengage the ball plunger from the detent. The shallower the detent angle (larger 0) the less force will be required to disengage the ball from the detent.

Installing A Spring Loaded Plunger

It is usually best to countersink the tapped installation hole to ensure correct alignment and to engage the nylon patch properly. Use a 90° countersink slightly larger than the thread diameter. Make sure that the threaded hole has enough complete threads to accommodate the entire length of the plunger. Use a bottom tap or tap all the way through the hole. Spring loaded devices are hollow so care must be taken not to over-torque when installing.