Which grade of Locktite to secure threaded brass to Aluminium?

G'day all. Making steady progress with my rotary fly tying vice.

I have decided on aluminium knobs for the vice with 0 BA and 2 BA brass screwthreads attached (mainly because I have a stash of brass BA screws and a P&N BA tap & die set).

I intend to tap the knobs to the appropriate BA size, screw in the appropriate screw tightly before machining off most of the slotted screw head. So which would be the appropriate grade of Locktite to make a permanent bond?

I have been looking at Loctite 263 but the website is a bit vague. All I learned is that one does not require a primer as brass is involved.

* Danny M *

P.S. Please do not ask for details of the vice as it is an 'on the fly' build (pun intended) but photos might be available if it works out OK

Loctite high strength retainer 638. It's intended for cylindrical fits but I have used it on permanent screwed assemblies. Just screw it together quickly no second chances.

Russell.

I agree with Russell ...

Any of the 'anærobic retainer' grades would probably be entirely adequate, as would 'stud-lock' ... but 638 is the obvious choice for any 'permanent' fix.

It will be a little slower to cure because of the aluminium; but the copper in the brass acts as a catalyst/activator, so yes, you may need to act quickly.

MichaelG.

+1 on the "act quickly" if using a catalyst.

Preferably do a test piece first - identical material, surface treatment, etc. Some years ago I came within an ace of screwing up a mega-expensive job. New bottle of retainer, new activator, and I reckon I had ~10 seconds before it was good-night. I had another three to do, so I made a jig that allowed me get the joint together and adjusted well within that initial cure time. Really worked well, though. The have survived ten years of rugged shipboard and underwater use without even a hint of a problem.

Roger

Thanks for all the advice.

Went into a local hobby shop and found this: **LINK**on the shelf for a few $. A small bottle but it looks good as I rarely require to make 'permanent' bonds and also much cheaper (<1/2) than the local Loctite distributor when I asked for for the similar stuff (on backorder until Feb anyway).

24 hour cure is good, it means that I might be able to screw the parts together in time. I don't mind waiting.

* Danny M *

Edited By Danny M2Z on 21/12/2016 04:31:52

The galvanic potential between brass and aluminium is 0.53 volts. This is a bit high. You may find that the parts will weld themselves together over time and you may not get them apart again - the Loctite may not be necessary!

If the parts are a interference fit, the corrosion may cause swelling of the joint and you could end up with a crack.

If the job is a only a temporary fix then disregard the above.

Alan.

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Danny,

I hope your chosen product will serve your purpose ... But will admit that I am surprised by your choice.

The opening question seemed quite specific [although admittedly I did assume that 'Locktite' was a typo.]

What you have is not a grade of Loctite, nor [perhaps] intended for a permanent bond [in the sense that the 'retainers' are].

MichaelG.

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Edit: Just checked on my memory ... and Yes, it was you that started this thread:

http://www.model-engineer.co.uk/forums/postings.asp?th=118701

Edited By Michael Gilligan on 21/12/2016 08:35:33

Edited By Michael Gilligan on 21/12/2016 08:52:53

Yep, Locktite was a typo for 'Loctite'. My choice was driven by the requirement to secure (permanently) a brass screw into a piece of 2024 aluminium alloy. Normally I would just 'do it up tight' and hope but in this case I decided to try one of the 'modern' adhesives.

Local industrial bearing shop did not have the required grade of Loctite in stock, advised me to wait until February and the cost for a tiny bottle would be $16.95.

So poking around in a local hobby shop I found the 'Zap' stuff for $ 6.50 and decided to give it a go.

As my fly tying vice is not expected to run at more than 60 RPM and be subjected to the torque of fine silk thread I am hoping that Zap Z-71 it is up to the task. Time shall tell!

* Danny M *

Like many topics, this one is a tad short on detail. How deep are the threads to be screwed into? 2mm might require a different approach than if the thread could be 20mm. Are the screws 'bottoming out' in the thread?

Danny,

Your purchasing decision seems quite logical, and I think it reasonable to assume that Zap Z-71 will do what you need.

That said ... I have found no technical datasheet for it, and the link to the MSDS didn't work for me; so I am relying solely on the package 'blurb'. ... It would appear to be broadly equivalent to the heavier-duty thread-lockers from Loctite and others.

When you come to use it; could you please let us know how it performs.

Thanks

MichaelG.

As a twist to this discussion, I feel it's quite pertinent to ask about what materials cannot ​be thread-locked?

I know some plastics fall into this category...

Michael W

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The Loctite anærobic threadlockers and retainers [and presumably those similar products from other manufacturers] are known to cause embrittlement of polycarbonate. ... I seem to recall that Tamiya supplies an alternative which is 'safe'.

Other than that; there may be problems with adhesion to some materials BUT threadlockers work mainly as gap-fillers rather than adhesives, SO with careful joint design, many apparent difficulties can be worked-around.

MichaelG.

Edited By Michael Gilligan on 21/12/2016 14:32:41