Which fit is the right one?

Correct torque application to the transducer is crucial for measuring torque. It is the only way to obtain precise and reliable measurement results. Torque is applied mainly via flanges using a friction joint, a method that has proven its worth a thousand times over with torque flanges, for example T12. Here a choice has to be made between ease of mounting through loose running fits or small unbalance through minimal clearance. In many cases, no flange is available at the customer side, but instead a shaft stub. In this case, choosing the right fit is extremely important. It is the only way to ensure correct torque introduction with dynamic processes, too.

DIN 7151 [3] or ISO 286 provide basic information for selecting the right fit. Figure 2 gives a first overview.

Choosing the right fit depends on the mounting and dismounting options at the user's site. In general, the user can choose freely to ensure correct torque application in all conditions of use. However, the user has sole responsibility for obtaining correct measurement results. Application examples and types of fits are specified in [4]. Fig. 3 shows an excerpt.

There are various possibilities for connecting shafts with holes. Be it interference and transitions fits, clearance fits, clamping connections or feather keys - the right manufacturing tolerance is crucial to the quality of measurement. HBM offers extensive support. Our tip: Do not refer to the data sheet only in the design, use the mounting instructions, too. Documentation for all torque products can be downloaded from HBM's web site at any time. In addition, the technical articles about frequently asked questions, available on the Internet, are very useful.