Stripped aluminum threads. Now what?

[brucemc777Participant @brucemc777]

The help i am getting from this board is truly amazing, especially in that the first board i posted to a week prior to posting here has yet to have one response!

First i should mention that no dogs were hurt in the making of this question… i’ll note so much as that she ripped the bench up and several feet from where it was, all she wanted was for me to throw her dang ball to play fetch. She’s rather “high energy” and i often think i should have named her “Stitch” from the 2002 movie-

One of the few pictures i saw for Rivnuts looked like the item had some depth and would grip by expansion. I appreciate the caution and am rather glad as i now have a solution for when those circumstances dictate.

Coils from Amazon arrive today! Fortunately or unfortunately, i work from home and do need to work (did so long before COVID-19 made it a fad), hope to install an a/c compressor and drier, evacuate and recharge the system in a daughter’s car today which is to be hot and awful humid (Portsmouth, Virginia, USA), so i will just have to play it a step at a time and see how it goes-but i do intend to post a picture (after i take it…) of the work to be done.

Thank you everyone for being there to help; i truly appreciate it!

-Bruce

[old martParticipant @oldmart]

For really desperate repairs in hollow sections, it might be possible to fit a close fitting solid piece of metal inside the damaged area. That would allow much longer threaded holes for strength.

Aircraft don’t use rivnuts very often, there are superior systems out there, but at a high price.

[brucemc777Participant @brucemc777]

It is a sealed area, though it wouldn’t take much for it to become unsealed and adapt for a bolt or the like.

Now, what really surprised me was the depth of the metal. I took an auto brake pad measuring tool out there and i was exactly right! 8mm. That doesn’t happen very often-

And… about the closest this thing came to being an airplane was when it flew when Daisy had taken it for a run.

 

I’ll probably go with long studs so they top out at the upper part of the inside space, figuring that little extra should give it a little extra support.

 

[bernard towersParticipant @bernardtowers37738]

Helicoil or double threaded bush and bobs your!!!

[Bill PhinnParticipant @billphinn90025]

Good to see what we’re dealing with, Bruce. It looks like the manufacturer cheaped out on fasteners that weren’t exterior grade. It might be worth replacing them with stainless. Use some grease or anti-seize when assembling to prevent galvanic corrosion between the aluminium and steel. And then perhaps paint over the finished assembly.

A wire thread insert or bushing, as Bernard suggests, should put things right with the damaged hole.

[brucemc777Participant @brucemc777]

My apologies to any ladies out there, this is NOT a sexist comment, just one particular to an individual: My wife doesn’t know the difference between black walnut and mdf (particle board), and i can’t explain it to her for two reasons: 1) She gets all upset that i think she bought trash, and 2) within a week she’s forgotten. Oh, and a possible third – after 30 years of marriage and four daughters i’d like to avoid a divorce-

[rjenkinsgbParticipant @rjenkinsgb]

I’ve used this type of thing – thread reducers:

You can use a standard tap of a larger size then just loctite the reducer in, to get a new thread of the wanted size. No special taps or kits required. Not appropriate for every situation, but a simple fix for some problems such as the OPs.

(They are also useful in smaller sizes when you need a small very deep thread in metal that does not clear easily – eg. you can use an M6 tap rather than M4, and then a reducer).

Edit – I forgot this site does not work with amazon links.

[old martParticipant @oldmart]

The area around the stripped hole looks plenty deep enough to drill close to breaking through and then accept a common 1 1/2 D length coil. You could practice by drilling and tapping a spare bit of metal right through. Then fit the coil, and you can then wind it right through and reuse it. If the coil you fit ends up with some still sticking out of the blind hole, you can cut off the surplace with a Dremel. Dont forget to use a little lubricant when drilling and tapping. A common fault with beginners is to push down on the fitting tool,very little force is needed, too much and the tang will break off prematurely.

[brucemc777Participant @brucemc777]

OK, so it’s held for two days now!

[jimmy b]

On jimmy b Said:

On howardb Said:

On jimmy b Said:

Rivnut sounds most promising to me

 

Jimb

Rivnuts are not a thread repair system, they are a means to achieve a threaded attachment point in a sheet metal assembly, such as an aircraft wing skin.

Agreed, in principle, not sure about aircraft wings though….but the question was about a suitable thread repair. From the sound of it I would give it a go.

 

Jimb

The first rivet nut was created by BF Goodrich in the 1930s, and sold under the trademark RIVNUT®. It was first used to mount rubber de-icing boots to aircraft wings.

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