Thread Galling

[rckendall]

This is a metallurgical question probably, but I figured this was the best area to post my question.

I threaded a fixture from aluminum with a tap, then a couple weeks later threaded the shaft, also from aluminum with a die. They fit perfectly together and I was happy. I cleaned the cutting oil from both pieces with Brake Clean in preparation for final assembly using locktite. Just to double check everything, I assembled the pieces together dry and while unscrewing them, they locked up and I was not able to get them apart. In the end they are ruined and I will need to remake them.

Being self taught in most things, I accept failures as a price I must pay, but I want to learn from my failures. I've known of SS threads having a tendency to gall, but is it any like materials or?????

Thanks for any wisdom offered,
Richard

 

[rr2030]

They are the same material ? Did they thread together easily ? One or two assemble-disassemble should not have caused galling if the threads fit correctly. Usually some movement over time is necessary for galling IE: thermo-cycling, vibration, etc.

If you were goin to loc-tite them any way, why are they ruined ?

 

[Gottschall]

use kerosene with alu. threads

 

[gunsandgunsmithing]

Likely a bit of debris remained somewhere after the brake clean wash or was displaced while assembly/disassembly and found its way to where it could create interference and hence, a gall.
Virtually anything can gall, especially dry. It only takes a speck of debris or a tiny burr.

 

[rckendall]

They are the same material ? Did they thread together easily ? One or two assemble-disassemble should not have caused galling if the threads fit correctly. Usually some movement over time is necessary for galling IE: thermo-cycling, vibration, etc.

If you were goin to loc-tite them any way, why are they ruined ?

I can't recall very many details, as everything was going as I expected. I will note that the male threads were up against a shoulder, and I had turned the die around backwards in order to get the threads to full depth in that area. I also made a small undercut at the shoulder.

Even while dry they went together well, but as I backed off a few turns, things turned wrong, and now they are locked up several turns from "home".

I think I would have been fine if I had just applied the locktite after cleaning and put them together.

Richard

 

[Alex Wheeler]

If you want to seize 2 parts together, use brake clean. It works very well.

 

[deanq]

They are the same material ? Did they thread together easily ? One or two assemble-disassemble should not have caused galling if the threads fit correctly. Usually some movement over time is necessary for galling IE: thermo-cycling, vibration, etc.

This is so NOT true! Two same metal components can gall anytime. Stainless is very susceptible as are many aluminum alloys. Your threaded parts galled. lubricate until your final fit, clean and then apply thread locker and then thread/torque.

 

[rr2030]

This is so NOT true! Two same metal components can gall anytime. Stainless is very susceptible as are many aluminum alloys. Your threaded parts galled. lubricate until your final fit, clean and then apply thread locker and then thread/torque.

Uh where in my post did I state same metals don't gall?? We are speaking galling not electrolytic action correct?

 

[Cloudrepair]

I can't recall very many details, as everything was going as I expected. I will note that the male threads were up against a shoulder, and I had turned the die around backwards in order to get the threads to full depth in that area. I also made a small undercut at the shoulder.

Even while dry they went together well, but as I backed off a few turns, things turned wrong, and now they are locked up several turns from "home".

I think I would have been fine if I had just applied the locktite after cleaning and put them together.

Richard

You could try freezing them and adding a couple dropes of oil and try blowing it into the joint then remove.
if you can fit them in a freezer?

 

[savagedasher]

This is a metallurgical question probably, but I figured this was the best area to post my question.

I threaded a fixture from aluminum with a tap, then a couple weeks later threaded the shaft, also from aluminum with a die. They fit perfectly together and I was happy. I cleaned the cutting oil from both pieces with Brake Clean in preparation for final assembly using locktite. Just to double check everything, I assembled the pieces together dry and while unscrewing them, they locked up and I was not able to get them apart. In the end they are ruined and I will need to remake them.

Being self taught in most things, I accept failures as a price I must pay, but I want to learn from my failures. I've known of SS threads having a tendency to gall, but is it any like materials or?????

Thanks for any wisdom offered,
Richard

Sounds like you’re using a starting tap

 

[paperpuncher]

I my experience aluminum and brake clean = no bueno. I dont have a scientific explanation but when using brake clean on aluminum have had some strange things occur

 

[Alex Wheeler]

I will share a method I have found to save you butt if you start to feel a gall. Stop before you make it worse and get some moly D tapping fluid. Warm the joint with a propane torch and drip the moly D into the thread. The heat will pull it in and the part will come apart with little damage.

 

[gunsandgunsmithing]

I will share a method I have found to save you butt if you start to feel a gall. Stop before you make it worse and get some moly D tapping fluid. Warm the joint with a propane torch and drip the moly D into the thread. The heat will pull it in and the part will come apart with little damage.

Good advice. Thread cutting oil is maybe the best lube for the job but as you said, stopping BEFORE you make it worse, is the real key here.

 

[Alex Wheeler]

Moly D is the key. Its great stuff. Also the best I found for tapping 8-40 threads in actions.

 

[tomswede]

There is probably a good answer, but why aluminum male threads? Aluminum usually calls for threaded inserts but aluminum make threads are really not used many places for good reasons.

 

[gunsandgunsmithing]

Moly D is the key. Its great stuff. Also the best I found for tapping 8-40 threads in actions.

Moly D is good. I have my own concoction that I've found to be even better for threading and chambering but my point was, greases and anti-seize is greatly overrated in this application, where many consider them to be superior. The real trick to any gall is to not force it...one finger tight can be too tight. It really depends on one's level of experience with feeling a problem. It's very hard to quantify feel, in this regard. By definition, a gall is created by friction and adhesion. Heat can be of help but it's likely too late for grease or anti seizes once a gall occurs. Kroil can even work but I agree that a good thread cutting oil is best if you can get it where it matters.

I find that a lot of times galls are self inflicted by not having a proper flat on the top of v threads....particularly with a tight fit. Virtually every thread should have a flat on top. There is absolutely nothing gained by a v thread that doesn't have the crest knocked down and the flat width is specified for each thread pitch.

 

[rckendall]

I find that a lot of times galls are self inflicted by not having a proper flat on the top of v threads....particularly with a tight fit. Virtually every thread should have a flat on top. There is absolutely nothing gained by a v thread that doesn't have the crest knocked down and the flat width is specified for each thread pitch.

These were small, 5/16" threads and I only know that I was under the nominal for the male thread and I don't remember the details of the female thread, but I will keep this in mind in the future.

Thanks to everyone for the help.

Richard