The Experts: Can Nord-Lock be used on inclined contact surfaces?

Q: Normally a mating surface is flat but sometimes it can be slightly inclined. What is the maximal angle of surface inclination where the Nord-Lock wedge-locking system can still work successfully?

A: In order to ensure that the bolted assembly is safely secured by Nord-Lock washers, the incline of the mating surface should not exceed 2.5°. It’s important to remember that tightening a bolt on an inclined surface introduces bending and increases the equivalent stress in the fastener. It may therefore yield at a lower preload than expected.

Due to the uneven load distribution when tightening against an inclined surface, the thread jams will increase friction and reduce clamp load as a result. This means that the full capacity of the bolt cannot be utilised no matter what locking system is being used.