Self locking screw?

[logbook]

The task is mechanically mounting an electrical circuit board (pcb). The mechanical engineer on the job prefers to use a stud into the chassis and a Nyloc nut. The Nyloc won’t come undone with vibration. I would prefer to use a screw as it takes up less board space. The Nyloc needs a big clearance for the nut spinner and is therefore non-ideal.

I don’t particularly like shakeproof washers or threadlock, and in any case the shakeproof only works until the screw becomes loose. A Nyloc is tight even after it is undone a little bit.

Is there such a thing as a self-locking screw with the excellent characteristics of a Nyloc? (Screws with captive shakeproofs (SEMs?) would not count as a Nyloc replacement).

 

[drawoh]

logbook,

You can get screws with nylon plugs in them that work sort of like Nyloc nuts. There are a number of suppliers, including W.M Berg, Nordic and Stock Drive Products. These are nowhere near as reliable as the Nyloc nuts.

You can get screws with deformed threads. These cause damage to your tapped holes. These holes probably are in something much more expensive than your screws.

The MS21043 ring based hex nuts are self locking and tiny and will occupy less real estate on your PCB, but they still damage the studs you screw them down onto. Can the stud be made replaceable?

Do not use the regular Loctites such as 242 on PCBs. They dissolve a lot of electronic components.

Lately, I have been specifying the torques on the screws on my PCBs. If you have enough screws, they are tightened down properly, you have a rigid base and nothing can wiggle about, they should stay tight.

JHG

 

[sreid]

Depending on the application these plastic snap on stand offs are easy to use.

http://www.keyelco.com/kec/standpro/prodcopy/prod15.htm

 

[MintJulep]

In addition to the Nylon plug or patch screws, there are a number of pre-applied "loctite-like" chemicals that can be applied to the screws. Since they are pre-applied, they are not messy like liquid thread lockers.

 

[CoryPad]

My recommendations in order of best performance:

1) Proper preload from a regular screw + nut to avoid any loads applied, including vibration

2) Pre-applied thread adhesive (3M Scotcg-Grip products are great)

3) Thread forming screw into unthreaded hole (try Taptite or Plastite, or maybe a PT screw.

Regards,

Cory

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

 

[yates]

Cory's got it right again ! there is no substitute for correct preload on a nut/bolt. There are various patented 'plastic patch' type locking devices on screws (Wedglock, Eslok...)but their performance would be between 2 and 3 on the Cory scale.

 

[CoryPad]

[blue]yates[/blue] - thanks.

I misspelled the 3M adhesive - it is supposed to be Scotch-Grip.

Regards,

Cory

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

 

[logbook]

Thanks to all respondents for some interesting thoughts.