Best material for anti-galling on aluminium thread?

[hobbs101]

Hi. I've got an M40x1 threaded hole in a 12mm plate of aluminium alloy (6082-T6). An threaded adjuster bar sits in the hole. What's the best material to make the bar out of to prevent galling? I'm thinking brass, bronze or aluminium bronze. I am also able to use lubricant e.g. grease.

Hobbs101
Mechanical Design Engineer

 

[drawoh]

hobbs101,

Anodize the aluminium. We have no problem screwing anodized aluminium parts here.

My next choice would be brass or bronze.

--
JHG

 

[Jughandle]

Some anecdotal comments:
I've always preferred ACME class 2G or 3G thread forms (not sure about a metric equivalent); seems like they are less prone to galling. Also the ability to use lube or anti-seize compound I see as a huge plus. Material-wise, I think your choices are OK, even steel (bare or phosphated depending on your particulars).

 

[KENAT]

Don't just use 'lubricant' pick a true anti galling/anti-seize compound stated to work on your selected material combination.

Is the thread heavily loaded, may impact what mating material you can use. I don't think I've ever had an issue with zinc plated steel into aluminum but haven't played with threads that big. Once in a blue moon do have issues with small stainless fasteners seizing (I assume galling but haven't verified) in 6061-T6. Generally impractical to reliably anodize smaller threads. If it's an adjuster that is routinely actuated and heavily loaded I may have some concerns using anodize - wonder if the aluminum oxide layer would tend to wear the mating screw.

A trapezoidal thread does exist for 40 mm

https://mdmetric.com/tech/thddat16.htm

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Tmoose]

Is the adjustment involve rotating equipment?
Is there a jam nut on the M40 adjuster bar.

 

[3DDave]

Kenat - we had a series of problems with stainless. It turns out that surface roughness was the best guide to problems. Rougher screw = more likely to gall.

If anodizing the aluminum, recall that there is a significant change in diametral clearance due to build up. Clearance decreases by at least twice the anodize thickness (i'd have to check again, but it's because the threads are at a 30 degree slope and the radius change is thickness*1/tan(30)

 

[Tuckabag]

If you're considering a coating, have a look at nickle/PTFE coating.
We've used NicoPTFE before on threaded parts and it is tough and very slippery.
Only issue is going to be build up on your M40x1 thread.

 

[drawoh]

3DDave,

The anodize process itself adds material, however, the anodizer usually etches the part to clean it and create a consistent finish. The total anodize process usually (not always) reduces the size a bit.

In any case, your drawings should have a note stating that the dimensions and tolerances apply after finishing.

I have designed lots of lens mounts with M50X0.5 threads, and even larger. The 1mm pitch seems rather large to me. If the same shop does both pieces, they will make them fit.

--
JHG

 

[hobbs101]

Thanks all for your help.

I'm using brass. The ally threads won't be anodised.

I understand with hard anodise the anodise build up is generally half of the anodise thickness.

Hobbs101
Mechanical Design Engineer

 

[mfgenggear]

I would have to repair jigs and fixtures that were made of aluminum tooling plate, the threads would allways strip out. repaired with threaded inserts, aluminum sucks for threaded holes.