Locking mechanisms

[mit227]

I will be using a plastic screw and a rubber washer to mount an electronic board. This board will have to undergo small amounts of vibration that i feel might affect the screw.
Any ideas of how to keep the screws from backing out. i may not use any metals!
thank you in advance
WJM

 

[mullins]

Loctite. (

http://www.loctite.com)

Apply a little to the male threads and bolt it down.

Taking the science out of rocket science...One step at a time.

 

[drawoh]

mit227,

Use really cheap, low quality screws with misaligned threads and flash from die casting.

Watch out for Loctite. Depending on the plastic and the Loctite, either it will dissolve the plastic or it will not adhere to the plastic. Loctite 242 dissolves all sorts of things on PCBs that you should not dissolve. I see testing in your future.

Is there any chance you can use ceramic screws? These will be expensive, but they will allow you to use more torque.

JHG

 

[mit227]

Loctite would not help us much. we use it quite a bit over here but in this situation it is infeasible.

Ceramic screws was an idea someone brought up at a meeting, but was never fully looked into. I guess now is a better time than ever.

i appreciate the interest. Any further ideas?

 

[KENAT]

Can you get those nylon patches for the plastic screws, I'm thinking there may be problems but it's an idea.

Otherwise, if made of a suitable plastic, why not have slightly deformed screws (or the female thread if it's plastic) to do the same job as the nylon patch (as drawoh kind of says)?

KENAT, probably the least qualified checker you'll ever meet...

 

[dgowans]

Do you have the flexibility in your design at this point to use a snap-in standoff? What are you mounting into?

 

[Screwman]

Use a heat treated steel screw and a nylon insert locknut. If you are having vibration I would worry about the nylon screw failing before I would worry about loosening. Nylon screws are terrible for fatigue properties.

 

[MiketheEngineer]

How about a drop of Epoxy or Super Glue??

If it works - you probably will never get it apart w/o destroying the screw --- but so what??

 

[Tmoose]

http://www.suspension.com/9-4102.jpg

You want rubber on both sides of the board and maybe even controlled crush to provide vibration isolation.