Stainless Steel Thread Galling

[Dave K]

I beleive in the original post I mentioned it's 303 stainless. It's not too fancy. Just a 5/8 shaft with a 1 inch head on the end. And we're just trying to attach the head to the shaft and make it extremely secure. Not just for rattling purposes, but to prevent theft.

[Dualkit]

How about designing it without threads and pressing the 2 pieces together? Or cross drilling
it and pressing a pin cross ways to lock the 2
pieces together?

[Dave K]

The pin Idea would infringe on a Masterlock patent.

I beleive he has the fix figured out now. He decided to thread the shaft by thread rolling, tap the head with only a 50% thread, but not thru the head, and then slide it on over the shaft from the opposite end. It will only thread on until it runs out of thread in the head, and then it's locked in place. It can't unscrew one way because it has run out of threads, and it can't unscrew the other way because it will be up against a trailer tongue when it's installed.

[JM Scott]

Shop for forged headed pins. Or take an unthreaded SS bolt and turn corners off head. In volume, it will be cheaper than making something in house. If you want to make it, grind a bevel on one side of end, press on head, tack weld in the beveled spot and finish grind end on a belt sander. Sanding will smooth and remove weld discoloration. You could even thread on the head and then sweat soft solder threads. 95/5 refrigeration solder makes a very strong joint.

[Bobw]

I've had to plug some holes in aluminum castings, and I found the easiest way was to turn my plug with a Pitch Diameter that was slightly larger than the pitch diameter of the tapped hole that was getting plugged. Interference fit the whole way, worked like a charm.

Or if you are using store bought hardware, how about 10mmx1.5 into a 3/8-16. Thats guaranteed to screw up the threads bad enough that nobody will get it off, as long as your going deep enough with the threads. Throw some locktite in for good measure.

Actually I wouldn't worry about it being completely impossible to remove since your shaft is only 5/8, and its only 303, a big set of bolt cutters or a hacksaw will make really quick work of it. Probably do it with a swiss army knife.

Aren't most of the $$$ bike locks made with hardened steel of some sort, of course you just said a "lock" and if the shaft is concealed in something else, then ignore what I just said.

[Dave K]

It's a reciever lock. It is very close fit to the rest of the reciever body. Makes it imposible to get a bolt cutter at the shaft. A hack saw would be hard to say thru also because the shaft will just spin, unless the guy also holds the head with a channel locks or something. It will never be failsafe, but at least he wants to make it as difficult as possible.

Jm Scott,

I guess I should have explained more in the beginning. there are other features on the other end of this shaft. It needs to be able to be done on a lathe with live tooling, and bar fed. This way it can be run on a machine that is unmanned. Using commercial bolts just turned the job into a chucking job. He's trying to keep costs down. These have to look fully machined and ultra clean while in the package on a store shelf.

[appliedproto]

Not sure if this area of technology is suitable for your project or materials, but one of my customers are starting to use Stir Welding for some of their larger aluminum structures. Apparently this process can join dissimilar metals, and it's a localize area of heat transfer. Same idea as with frictional welding, like how they attach impellars to shafts very accurately and with little affected area.

[Dave K]

Stir welding sounds interesting. Can it also join like metals?

[Frederick Harvie]

If there is a very slight intentional mismatch of the thread the two parts can be assembled and the galling will make the assembly permanent. In my experiance with this situation a bigger wrench will not help, you would be more likly to twist of the bolt then to remove the nut.

[pepo]

There is a process called "inertia welding". Assuming I understand your needs,they would put the shaft or pin in a spindle like a lathe and put the collar in a holder on the same centerline. With the spindle turning at an arrived at speed the shaft is forced into the collar with an appropiate amount of force. The resulting friction inertia welds the 2 peices together. Trust me,it is permanent. And also an interesting looking joint. The heat is localized enough to not make an ugly part. If quanities are high enough cold heading may also be an option.

[Dave K]

Thanks, Pepo. I suggested cold heading and inertia welding, but either one would turn the job into a chucking job, which will cost more for the machining. Also, friction welding would probably scratch up these parts. They are machined to at least a 32 finish, and can't be all scratchy when they hit the store shelves.

[SND]

620 Loctite.

[hello113]

or 271 loctite, never used 620 better than 271?

[SND]

271 should work fine. I forgot about that one as I haven't used it in a while. It is defenatly meant for threads, although I've taken out a few stainless threads that had 271 on them.

The 620 is green, can take up to a .015" gap ( on diameter). We most mostly use it for a different application but when we've put it on threads that we didn't plan on ever taking back out. Wasn't much fun when we found out they had to come back out.

Whatever you end up doing with, given the application a good test seems in order. Welding would be the safest bet and a good welder can make anything pretty. With bonding compounds you have to be sure that they will last and be up to the task and the weather. Just like galling threads together wouldn't necessarily yeild the same results every time, and there's little way to gage how well it is stuck together. Other than the " wow that thing really doesn't wanna come back of" .

[Chris999]

Depending on the precision of the production processs I'd recommend a .003 to .005 press fit and then heat the head and shrink it on. I think this may cause a appearance and subsequent cleanup problem in your case. If the loads are light, could you use a .002 press fit and do it cold?

This is hard to visualise well without a pic, but if it's just a shaft with a round head, can't you have a slip fit and then TIG weld it on on the inside corner where it can't be seen? Even a poor welder with a rotary fixture for welding can do a nice job, and then clean it up with a fine wire brush or electropolish.

[Dave K]

Sorry guys. Weld would be right out in the open. Here's the actual lock. http://www.life-longlocks.com/

See how weld would would look on a product like this? No matter how well it's done, it would appear shabby looking compared the the rest of the machined part.

[BazMan22]

If he's looking to save money, I'd go with Stainless Steel Fittings. I get my fittings from there and the prices are pretty great

[SteveEx30]

Just sprinkle both pcs with a fine abrasive media, then screw together. They will definitely gall up and will never come apart. It also won't affect cosmetically.

Ask me how I know this....

[Sparky961]

I'd say since the project has been sitting on the shelf for over 10 years now the thing has probably welded itself together.

(This one is more than a little past it's best before date)