Fastener locking (again???)

[drawoh]

I am competing the drawings on a panning base with a harmonic drive gearset. The device operates intermittently, so I do not have cooling problems and I can lubricate the thing with grease.

I intend to attach fasteners without threadlocker. I am not sure how well threadlocker operates around grease, and I have some delicate electronics components that will be dissolved by regular threadlockers. I have worked out my screw torques based on unlubricated threads. I want the screws all locked down as tight as possible.

One of the reasons I normally like to specify Loctite 242 and its equivalents is that these are lubricants, at least until they harden. I assume that the thread's behaviour under torque is more consistent than it would be unlubricated.

What would happen if I specified that the screw be greased before assembly? Grease is being used for the assembly anyway, so there is no problem with logistics. Obviously, a greased screw on its own, is more likely to come loose. On the other hand, the greased screw ought to be installed with a more consistent torque, and the high initial torque should prevent loosening.

Any thought?

JHG

 

[MintJulep]

Grease is generally recommended as a lubricant for threaded fasteners. You are correct that a lubricated fastener will reduce the scatter in achieved pre-load if you are using torque to control the tightening. You will need to recalculate the torque for lubricated values. If it is really important you should test to determine the torque vs preload relationship for your specific application rather than rely on published handbook values.

Have you considered either a Nylon patch or pellet in the fastener, or a pre-applied (dry) thread locking agent?

 

[CoryPad]

I agree that grease can be used as a fastener lubricant. I agree that pre-applied thread adhesive should solve your problems. I would avoid polyamide (nylon) patches or pellets - they have poor preload retention performance.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Tofflemire]

Hi Drawoh

Can you use lock washers?

Tofflemire

 

[drawoh]

Tofflemire,

All the literature I have been reading, including the messages in this forum, states that lockwashers make things come loose.

My parts are structurally rigid, and there is not a lot of room. If the parts are clamped solidly, there is no way anything can move.

My assembly strategy is to use as much tighening torque as possible.

JHG