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Shafts

Materials

Standard potentiometer shafts may be fabricated from stainless steel, brass, or plastic. Materials other than the standard shaft materials can be requested as needed for your customer's specific application.

Diameter

Your customer may need a larger or smaller shaft diameter than the standard sizes. The most cost effective way of increasing the shaft diameter is with a sleeve. Although utilizing a sleeve minimizes modification to the potentiometer, the shaft runout will increase. Avoid over specification and modification of shaft tolerances to obtain the most cost-effective design solution.

Length

The accepted industry standard for measuring shaft length is from the mounting surface (FMS) to the end of the shaft as illustrated in Figure 11.11.


Figure 11.11
Other Shaft Modifications

Unless otherwise specified, Bourns will assume that your application calls for a standard shaft configuration. When specifying custom shaft lengths of standard models, the shaft end feature must be included whether it is a flat, slot, or plain end. Custom flats must have the following specifications:

  • Length (l) of the flat from the end of the shaft, including the tolerance
  • Width (w) of the shaft, including the tolerance
  • Orientation of the flat, if required. For example, the flat orientation may be in relation to the wiper position at a mechanical stop, an end point, or the bridge area. The bridge is the area in a single-turn potentiometer that separates the two ends of the resistance element. Many orientations are determined by the application itself.
Custom shafts with a specified flat will not include a slot unless it is specifically requested.

Holes or other custom features requested must include the same type of detailed dimensions including orientation.

Rear Shafts

The best way to specify rear shaft length is from the mounting surface (1), or as the total shaft length (2) as shown in Figure 11.12. The rear lid can also be used as a reference point (3). However, this method may result in a tolerance build-up (housing and shaft tolerances).
Figure 11.12

Specify the rear shaft diameter along with its length and tolerance. Most standard shafts have the same diameter, front and rear.

Rear shafts are assumed to have a plain end, unless otherwise specified.