Bearing Clamping Force
All high precision bearings must be locked in place during installation. Generally, a threading component, like a precision nut or bolt, is used.
Whatever threading method you choose, it needs to have one goal: to keep the bearings tightly mounted on the shaft when installed.
This article outlines the steps you need to take before and during installation to ensure the proper clamping force is applied to the bearing.
Before getting started, locate this information:
- GMN max clamping forces for each type of bearing (our bearing catalog will help)
- What amount of clamping force is needed to get proper engagement
- Your application’s tolerance guide
Best Practice for Clamping & Securing Bearings
First lightly oil the precision nut or bolt threading. FYI: Thread locker is considered the same as ‘oil’ when applied to thread.
Make sure the thread isn’t 100% covered with oil before moving on to the next step.
Second, install the clamping component by hand and then use an accurate torque wrench to tighten the nut 2-3 times past the goal torque. Then back the nut off and tighten to the goal torque.
Note that the 2-3 times tightening ensures proper seating of the clamping component. This part of the procedure will make sure that if there are any thread imperfections it won’t hinder the proper clamping force.
Download our PDF guide on recommended clamping forces. Please note: These torque recommendations in the table are specifically for the nuts called out in the table. If a different nut is used the torque will have to be calculated from the clamping force. These forces are based on a safety factor below the plastic deformation of the bearing race cross section of the AISI 52100 bearing material.
These numbers may seem high, but they should be used as a guide for max force, remember that a clamping force that is too low can be just as harmful to bearing life as force that’s too high.
Clamping force that is too low is defined as being close to the factory preload of the bearing (i.e. L/M/S Newton values).
Clamping Force for Proper Engagement
Each application may have its own specifics that will affect the required clamping force. Using the GMN recommended clamping forces will remove most of these variables. However, a heavy press fit, differing materials, special coatings, etc. should be taken into account.
The clamping force and clamping apparatus needs to achieve a fully seated bearing. This is the goal, but it can be achieved in various ways.
A properly seated bearing is contacting all of the mating abutments and the races are axially aligned.
Tolerancing of all surfaces that influence the bearings is very important.
An incorrect tolerance stack up could:
- Fully seat a bearing without helping to preload it
- Overload the bearing
Both of these scenarios can reduce bearing life by a lot. A thorough axial tolerance stack up is required for all applications to ensure proper bearing preload (i.e. MMC/LMC analysis).
A spring preload does allow more tolerance flexibility, but be sure to not change the target force with too large tolerance window(s).