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December 04, 2020, 20:45:37 pm

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Making Self Tappers into Plastic Durable to Many Assembly/Disassembly Cycles

Started by e-flite_rules, November 21, 2020, 11:35:20 am

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e-flite_rules

Using self tapping screws to fasten together plastic items typically works fine.  That is until one tries to make and unmake the joint multiple times.  Sooner or later the thread strips and the clamping load drops to zero.  Not good if the joint is holding a wing in place!

I typically avoid this issue by never undoing such joints.  However space limitations in my house mean that all planes now need to be de-rigged for storage. 

So.....

Any ideas as to how to make such joints serviceable?  Typically they are blind so adding a captive nut behind the joint is not an easy option. 

Something like these would seem ideal.  However I only know of a source down to M4.  Need something more like M2.



So any ideas?

THANKS!

e-flite_rules

Maybe take a short countersunk M3 bolt and then drill and tap an M1.6 thread into it coaxial with the main thread?  Epoxy the bolt into an M3 countersunk and tapped hole in the plastic and then use a spring washer, plus plain washer, under an M1.6 bolt to provide a shake proof joint?

Or even use a countersunk #3 or 4 self tapper?  Do such things exist?

What do you think?


pooh

I can't find the item I wanted to show, I've used them in the past for exactly the sort of job you want. The version I have used is a partially split brass cylinder with a rough outside (sharp points) and a female thread ending with a brass disc which is only partially down inside the inner - as you screw into the thread (with a screw!) it pushes the disc further down the inner, which forces the split cylinder to push hard against the plastic hole.

I bought these from one or more of my usual electronics suppliers (my day job is electronics) but I'm blowed if I can find them in RS Components or RapidOnline, largely because I can't work out how to describe them to the search engine!

these guys may be able to help


https://www.insertsdirect.com/acatalog/Small-Quantities-1.html
Confucious he say "more than one aircraft in the same airspace leads to structural failure"

gavin mack

Gravity never loses, The best you can hope for is a draw
It takes 2 years to learn how to talk, and a life time to control your mouth.

e-flite_rules

Quote from: pooh on November 21, 2020, 12:34:50 pmI can't find the item I wanted to show, I've used them in the past for exactly the sort of job you want. The version I have used is a partially split brass cylinder with a rough outside (sharp points) and a female thread ending with a brass disc which is only partially down inside the inner - as you screw into the thread (with a screw!) it pushes the disc further down the inner, which forces the split cylinder to push hard against the plastic hole.

I bought these from one or more of my usual electronics suppliers (my day job is electronics) but I'm blowed if I can find them in RS Components or RapidOnline, largely because I can't work out how to describe them to the search engine!

these guys may be able to help


https://www.insertsdirect.com/acatalog/Small-Quantities-1.html

Thanks!  Just what I need to solve a different problem I have.  RCMF rules!


e-flite_rules