ABS plastic case and screws vibration issue!

[var10]

Hello again!

I am trying to hold two ABS plastic cases together with a M2 mild or stainless steel (pan head) screws. The problem here is vibrations during usage, though they are not very high I don't want loose back case during normal operations by customers.

I thought of using Thread locker loctite and they don't work on plastic.

I want them to be easily removed during repairs but prevent vibrations, so I thought of using spring washers between a flat and screw or a earth washer which probably digs in the plastic.

Or even i could just paint the screw heads which could potentially prevent vibrations.

Do you think any of the above might work or any other better suggestions please share.

Any help is appreciated.

Thanks

 

[SceneryDriver]

Loctite DOES make a "plastic compatible" thread locker, but it's really little more than a pricy bottle of Super Glue, near as I could tell. Can you through-bolt and use a ny-lok nut?



SceneryDriver

 

[var10]

Yes they make plastic compatible adhesives. These will permanent which I do not want. I spoke with a henkel rep and he said there is no thread lockers for bonding between plastic and metal screws.

Major design change - I am trying to hold an aluminium and abs part together.

I am seriously considering through bolt and nylock nut but space is a problem.

I don't know how good it will be during vibrations if i use a taptite screw through al.

 

[TVP]

I suggest investigating some thread forming fasteners or Spiralock threads. Here are some links for more information:

http://www.ejot.com/ejot.de/Product_Range--4800.htm

http://www.sfsintec.biz/internet/sfsinten.nsf/PageID/thread_forming_plastics

http://www.emhartamericas.com/brands/spiralock/technology

 

[CoryPad]

Based on your description, I think the best solution is a metallic threaded insert in one piece and a metallic compression limiter in the other piece, both connected with a screw (no washers) that is pretensioned properly to prevent loosening.

 

[racookpe1978]

I like the idea of threaded insert: a little higher price, but much more durable. Can you go to a larger screw? M2 is very, very tiny.

 

[var10]

No has to be M2 due to space constraints. I have decided use a torque driver with a specified preload and we will experiment.

 

[racookpe1978]

M2 screws make the term "fingertip pressure" very relevant. Its a good question - I've never considered having to control or measure very, very tiny torques. 8<) Hundreds of foot-pounds is more often my concern.

 

[var10]

According to my calculations I get a torque value of 35N.cm using so many approximations.

 

[racookpe1978]

35 N-cm's = 1/2 foot-lb? Sounds like too much to me.