Galled Stainless Steel machinist jack??

[ChazzC]

I whipped up a machinist jack the other day. I used a piece of stainless steel that I had laying around, it machines beautifully.
It came out great except it felt like there was some grit in the bore.
I placed both pieces in my ultra sonic cleaner.
When it was finished I screwed the pieces together. It got tighter and tighter. Maybe because the pieces expanded in the heat?
Now it’s ruined. I can’t budge it. It’s completely stuck. Scrap pile!!
I used a commercial tap and die to produce the threads.

What the heck happened??
Have you ever experienced this??

Don’t laugh at my knurling

Had that happen on a fabricated SS part for a BioChem project (on the day that we had a Big Wig tour coming in). The department machinist who made the part was off that day, so took it to the main machine shop: they were able to get the relatively cause threaded pieces apart using a six-jaw and 3-jaw of the two ends to apply torque with final surface finish damage, then relieved the external threads (single-pointed) and advised a light coating of pharmaceutical-grade anti-sieze. Didn't have any issues after this.

Couldn't use anything other than SS in the part due to the application, and it took the better part of a week to make it so it was a good thing they got it apart.

 

[Ischgl99]

So ya'lll don't think that freezing the screw with dry ice and heating the base with a torch would yield any result? Is galling really welding?

Galling is cold welding, material from both pieces fuses together from the friction caused by the parts rubbing. Once it galls solid, it’s not likely coming apart. With stainless on stainless, it is very important to stop what you are doing if you feel more resistance than you expect, especially if it progressively gets worse. If what happened here is galling, then heating and cooling probably won’t do anything, but it is worth the try in case the cause is something else.

Followup question: Does passivation help prevent galling?

It can, the oxide layer does not gall, the metal below it does, so passivating it might help. What’s more important is preventing any high spots in thread or sliding surfaces that will cause high friction, that will wear through the oxide layer in no time. And use a good thread lubricant, stainless threads should never be assembled dry if you can avoid it. This is what the factory supplied with the machines when I worked at the centrifuge manufacturer.

MOLYKOTE® 1000 Paste

A mineral-oil-based anti-seize paste formulated with solid lubricants such as copper, graphite, and white solids.

www.dupont.com

 

[Jake M]

I placed both pieces in my ultra sonic cleaner.
When it was finished I screwed the pieces together. It got tighter and tighter...

What the heck happened??
Have you ever experienced this??

My belief is that your ultrasonic cleaner took the oxide layer off of the outside. If you're not familiar (you may be), stainless steel is not stainless because it's not reactive. It's stainless because it's VERY reactive, and it flash rusts very, very quickly. The difference is that "stainless rust" is too tightly packed to let more molecules past it, so the inside layer is protected with a layer of rust that's literally one molecule thick. You can't really even see it. And of course nothing like that is perfect, it will thicken over time too.

while any metal is subject to it in the right conditions, stainless is very prone to cold welding. More so than most metals. Further, some grades are far more prone to it than others,

Galling, or cold welding (same thing by different mechanisms), or "adhesive wear" (which doesn't really apply here without load and speed, but is very related and kind of interesting) is literally what happens when "pure enough" samples of materials are in contact. There's nothing between them. They have no way to "know" that they are separate materials, and the molecular structures intertwine and arrange just as they do int he solid piece. They become one. That's cold welding.

I have no idea what stainless steel you were working with (nor enough knowledge to do anything with that information), but some stainless steels, when freshly cut by any means are VERY, VERY prone to this. I suspect that had you left the parts on the bench overnight before assembling them that this wouldn't have happened. At least not right off. Some pressure, a little vibration from a cutting operation, I bet it still would have happened, just not straight away.

18-8 and 316 are common stainless steels that are not "as bad" about galling/cold welding. (But they still will for sure). They are common for bolts, nuts, and threaded hardware. Soft though, very low torque stuff. I think 304 falls into that "safer" category as well. For lightly loaded stuff, usually a little oil, or nickel anti-sieze will keep fasteners good. We have some sidewalk salter stuff at work where the original hardware is 4XX something or other. You don't take those apart. If you put NEW hardware in to the prescribed spec, You never reach the tension, they just go until they stop, at which point they could be about any tightnenss, but they become one. And the torque wrench would might as well might as well be tensioining a cold set rivet.

 

[Janderso]

My belief is that your ultrasonic cleaner took the oxide layer off of the outside. If you're not familiar (you may be), stainless steel is not stainless because it's not reactive. It's stainless because it's VERY reactive, and it flash rusts very, very quickly. The difference is that "stainless rust" is too tightly packed to let more molecules past it, so the inside layer is protected with a layer of rust that's literally one molecule thick. You can't really even see it. And of course nothing like that is perfect, it will thicken over time too.

while any metal is subject to it in the right conditions, stainless is very prone to cold welding. More so than most metals. Further, some grades are far more prone to it than others,

Galling, or cold welding (same thing by different mechanisms), or "adhesive wear" (which doesn't really apply here without load and speed, but is very related and kind of interesting) is literally what happens when "pure enough" samples of materials are in contact. There's nothing between them. They have no way to "know" that they are separate materials, and the molecular structures intertwine and arrange just as they do int he solid piece. They become one. That's cold welding.

I have no idea what stainless steel you were working with (nor enough knowledge to do anything with that information), but some stainless steels, when freshly cut by any means are VERY, VERY prone to this. I suspect that had you left the parts on the bench overnight before assembling them that this wouldn't have happened. At least not right off. Some pressure, a little vibration from a cutting operation, I bet it still would have happened, just not straight away.

18-8 and 316 are common stainless steels that are not "as bad" about galling/cold welding. (But they still will for sure). They are common for bolts, nuts, and threaded hardware. Soft though, very low torque stuff. I think 304 falls into that "safer" category as well. For lightly loaded stuff, usually a little oil, or nickel anti-sieze will keep fasteners good. We have some sidewalk salter stuff at work where the original hardware is 4XX something or other. You don't take those apart. If you put NEW hardware in to the prescribed spec, You never reach the tension, they just go until they stop, at which point they could be about any tightnenss, but they become one. And the torque wrench would might as well might as well be tensioining a cold set rivet.

Wow,
Very informative. Thanks for taking the time!!

 

[Ultradog MN]

I whipped up a machinist jack the other day. I used a piece of stainless steel that I had laying around, it machines beautifully.
It came out great except it felt like there was some grit in the bore.
I placed both pieces in my ultra sonic cleaner.
When it was finished I screwed the pieces together. It got tighter and tighter. Maybe because the pieces expanded in the heat?
Now it’s ruined. I can’t budge it. It’s completely stuck. Scrap pile!!
I used a commercial tap and die to produce the threads.

What the heck happened??
Have you ever experienced this??

Don’t laugh at my knurling

Where were the tap and die manufactured?

 

[Janderso]

Where were the tap and die manufactured?

China
My good taps are under 1/2”

 

[Nesse1]

I work for a company that makes water and waste systems and components for the aviation industry, and we use tons of stainless to ward off corrosion. ALL parts are required to be "passivated" before usage. This involves a nitric acid dip, which removes any free iron on the parts, and then a passive oxide layer is formed, which wards off any further corrosion. We have some parts with stainless studs, and stainless nuts, and during install the nuts would gall, and then the studs would break off. Not good! The countermeasure was to use food grade anti-seize to prevent galling. Even our design engineers sometimes mess this part up. It's hard to envision how stainless on stainless can weld together like the parts discussed in this thread. It's FACT, though. Live and learn!

 

[GT-6 Racer]

The 300 series austinetic stainless steels are very highly prone to galling. Dissimilar materials help to some extent. Brass/bronze or even carbon steel are better when mixed with 304. If you need stainless for fasteners and it can be magnetic go for 400 series or maybe 17-4 PH. If you can tolerate the cost, Gall-Tough + from Carpenter is the best non magnetic stainless for fasteners.
into stainless a lot you need a reference.
If you can find a copy,

Source Book on Stainless Steels:​

from ASM is my reference for stainless use.

 

[tq60]

We had 800 mhz corner reflector antennas that had stainless hardware.

If it is oiled before use, it is fine.

If assembled dry, and you turn the nut too fast, you are done.

The stud would shear if the bigger wrench used.

1/2 inch size.

There are a few other brands that use the same, which can be a pain to remove after many years for weather to wash away the oil.

Sent from my SM-G781V using Tapatalk

 

[Flyinfool]

This is all good to know. I also use too much stainless!
So ya'lll don't think that freezing the screw with dry ice and heating the base with a torch would yield any result? Is galling really welding?
Full disclosure...here is my ill-conceived stainless machinist jack!

Followup question: Does passivation help prevent galling?

Heat and freeze, it the galling was really minimal, MAYBE. Most likely not.

Yes it is really welded at the molecular level. No penetration but the surfaces are actually welded. the friction is enough to generate the heat needed to weld in just the few molecules that are touching. That is why it feels gritty first as some molecules are starting to weld but the area of the weld is easily broken but that makes a rough spot that makes more friction and more welding, it just keeps escalating until it is welded enough to lock the thread tight enough that the bolt will break before the weld does.

Passivization does not make a difference one way or the other to galling.