Aluminum adhesive

[Peter Simpson 3Participant @petersimpson3]

I need to drill out some worn threads in aluminum, then insert an oversized blank. I will then retap the treads back on to the blank. The blank will need gluing into position before drilling and tapping. Tap size is M4 the blank is 6mm diameter. What is best adhesive for the job? There is very little load on the threads

[Clive FosterParticipant @clivefoster55965]

I find high strength loctite satisfactory for such jobs, the green bearing retainer stuff ‘cos I have it in stock.

As far as I know none that I’ve done, both for myself and other folk, have failed.

Where possible I like to leave a small plain rim on the bush screwing down into a matching counterbore. Bit more gluing area and I like to think that positive location from the top is more secure than simply running down a threaded hole. Figure there is reason why Timesert thread repair inserts are made that way.

Clive

[not done it yetParticipant @notdoneityet]

If you can thread the over-sized hole, a threaded insert would need just a dash of loctite-anything to secure it.

[Andrew EntwistleParticipant @andrewentwistle]

+1 for Loctite 638 or similar for this job

[bernard towersParticipant @bernardtowers37738]

I’m with NDIY

[James AParticipant @jamesalford67616]

I had a similar problem with a thin web on a motorbike crankcase. I drilled out the original thread and made an insert of exactly the same size as the hole. I roughened the outer surface of the insert (I have no knurling tool) and warmed the case enough to expand the hole for the insert to fit. I coated it with Loctite and pressed the insert in.

It is still holding firmly after several years.

James.

[not done it yet]

On not done it yet Said:

If you can thread the over-sized hole, a threaded insert…

In the situation described, the insert is 6mm dia., so presumably M6 thread and 5mm tapping drill. The other component has an M4 thread. That leaves a 0.5mm wall thickness.

Using M6 x 0.5 thread on the insert improves the situation. Using loctite and no thread at all improves it further.

[noel shelleyParticipant @noelshelley55608]

A rivnut is available and can be set by squeezing in a vice if no other tools are available.  Rivnuta are made in numerous metals to suit the job.   Noel.

[MacolmParticipant @macolm]

Wire thread inserts are another repair possibility if the worn hole is not too bad. A good indication is that there remains a slight witness of the original thread. Of course you need to buy or borrow the kit. The resultant threads are accurate, strong, and very durable if made of hard drawn stainless wire. Another benefit is that this needs the the least diameter increase for the repair.

[Phil super7Participant @philsuper7]

I would suggest using a helicoil these are made for such a job

[Nigel Graham 2Participant @nigelgraham2]

Phil – that’s what Malcolm suggests, “Helicoil” being simply a brand.

Be careful though if the finished work has to withstand corrosive conditions such as damp ground or salty water. Stainless steel in intimate contact with aluminium can result in the aluminum disappearing while the insert stays pristine.

Even mild-steel can have similar effects.

 

(I’ve sometimes wondered this in the case of miniature ground-level railways using aluminium rail and steel, especially stainless-steel, fishplate bolts.)

[MacolmParticipant @macolm]

Well yes, if conditions are seriously corrosive, the screws will also need carefull selection.

[Author]

Posts