Swapping steel washer for aluminium bracket

[DaveJFT]

Hi folks,

I currently have a bolted joint closing 2 aluminium housings using short steel studs, 1.5mm thk steel washers and Kaynuts. On two of the studs I need to replace the steel washers with an aluminium bracket (also 1.5mm thick) but there is not enough thread length on the studs to retain the steel washers in the joint. Are there any mitigations I need to make to accommodate this change?

Many thanks,

Dave

 

[Tmoose]

k nut =

https://k-nuts.com/wp-content/uploads/2012/09/ecrou-aviation-hexagonal.png

??

what does the bracket do?
What do the studs secure?
Is it a gasketed joint , with no limits on gasket compression when tightened?
Do you mind if the nuts embed into the bracket and the joint becomes loose?

 

[MikeHalloran]

Throw away the aluminium bracket.
Replace it with a steel bracket.



Mike Halloran
Pembroke Pines, FL, USA

 

[DaveJFT]

Thanks for the replies guys.

Steel would be the easy option. Unfortunately, being an aero application, weight is critical so steel is out unless Al is proven to be unacceptable. It would be carbon fibre if it could be.

The bracket supports a carbon fibre box of wires so there's no real weight in it and the joint is RTV sealed. As with most joints, it kind of is a bit of an isssue if the joint comes loose.

 

[Tmoose]

" weight is critical so steel is out "

How ornate is this aluminum wire-supporting bracket ?
Please post a picture.

===========================

I wonder which of these is lighter.

http://i39.photobucket.com/albums/e156/n1smo/Mazda3Speed/DSC_0487.jpg

===================

https://thumbs.dreamstime.com/z/jet-engine-12655594.jpg

 

[IFRs]

Can you use aluminum or SS nuts ?

 

[SnTMan]

Longer studs?

What's in the housing? What happens if two studs loosen due to embedment of the nuts in the bracket?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[tbuelna]

First, it's good that you are even asking this type of question. Even in the aerospace industry, many designers don't appreciate the importance of paying attention to details of something simple like a threaded fastener installation tolerance stack-up. One task I usually had to do for every threaded fastener installation used on an aircraft product was a tolerance stack-up at MMC/LMC. With the stud/kaynut installation described, the stud should have sufficient complete thread length to prevent the nut from "bottoming out" before the mating parts are fully clamped. The stud thread length should also be sufficient to allow at least 2 full thread pitches visible beyond the kaynut locking feature after installation, which is a typical QA requirement in aerospace.

With the example described in the OP involving an aircraft product, where weight is more important than cost, the correct approach would be to install slightly longer studs at the two locations where the bracket tabs are clamped, so that a washer can be used. Washers are typically used under the flange face of the fastener element being turned, which in this case is the kaynut. The washer protects the substrate surface from scuffing damage.