Cutting new bolt threads

[stonesfan68]

I recently purchased a grinder that has damaged threads on one side of the shaft. The threads are left-handed. I think that the previous owner tried to remove the nut by turning it to the left instead of the right. I managed to get the nut off with a nut buster. As you can see the threads are pretty buggered.





I am relatively certain that a traditional thread chaser will not fix these threads and that I am going to have to cut new threads. The current threads are 1/2 - 20 UNF.

If I purchase a 7/16-20 UNF left-hand thread die can I simply cut new threads over the old? If so, does anyone have any tips as to how to get the die started? I've seen some dies that are adjustable, are those easier to use? The most I've ever done with threads is use a thread file and a thread chaser.

Do the threads really have to be left-handed?

Thanks in advance for the help.

 

[PBCampbell]

Looks more like some hokey setup that left the attachment unsecured with the spindle just free enough to spin inside of it and eat the threads off. I'd be looking to just replace the spindle or getting another tool before getting into the cost of special dies that likely will never be used again.

 

[lilredex]

If your grinder turns the stones down toward you, then yes you need LH threads on the LHS. Otherwise it will just unscrew when you put that stone to work.

Why can you not use the good threads that are left, and make a spacer to cover those that are damaged?

Get two 1/2-20 LH nuts and make a simple chaser out of one of them. Like these.


free upload image

You have nothing to lose at this point.

 

[APEowner]

Yes, you need left hand threads. No, you can't just run the next size smaller die down the shaft. As lilredex suggested use a spacer to get the nut on the good threads.

 

[J.A.Varela]

Take it to an electric motor shop. They'll straighten it out for you.

 

[Fcvapor05]

You should carefully measure the remaining threads on the inboard side, to make sure the shaft hasn't stretched at all. If the shaft has necked down at all, it will not be safe to use at high speed.

 

[stonesfan68]

Why can you not use the good threads that are left, and make a spacer to cover those that are damaged?



Get two 1/2-20 LH nuts and make a simple chaser out of one of them. Like these.



You have nothing to lose at this point.

That's a good idea. How do I make a nut into a chaser?


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[Kevin54]

That's a good idea. How do I make a nut into a chaser?


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Get him so drunk that he has beer goggles, and then tell him the fat chick has the hots on him

Chances are that your shaft may possibly be like a Grade 5, so use a Grade 8 and see how things come out.

Or, if you have a HF around, look into a thread file to straighten them out. A thread file, although classified as a file, doesn't really cut a lot, but will fit the threads and more or less, move the threads somewhat.

 

[Steinmetz]

Agree. Try a thread file.

 

[A_Pmech]

That thing looks done. I'd do as several others suggested and space the nut out further on the shaft.

 

[Fcvapor05]

A thread file or thread chaser won't repair threads that no longer exist. To use that shaft you have 2 options- use a spacer, or replace the shaft.

I'll say this again, for your own safety, check the shaft and make sure it's not stretched before you use it. There's a LOT of energy ******* in a rotating grinding wheel, and if the shaft breaks it's going to hurt either you or your stuff.

 

[2oolhound]

Don't forget it's left handed so if you do use a thread file you have to flip it over and use it backwards to file left hand threads. Either that or try pulling it instead of pushing on it.

and now some useful information maybe - you could also try using an internally threaded arbor extension on it but that would move the wheel out past the guard.

 

[zkling]

That thing looks done. I'd do as several others suggested and space the nut out further on the shaft.

Geeze, to chase or even cut threads there has to be something there to cut into. I'd go for the spacer route.

 

[lilredex]

That's a good idea. How do I make a nut into a chaser?

Nut + hacksaw = chaser. Make the saw cuts about a third of the way down the nut. Install the nut on the saw cuts side. Any debris will be pushed into the cuts and the balance of the nut will straighten out what is left of the threads. Think this your best bet to salvage what is left.


I have a collection of those nuts and they have been used extensively to save the day........... gas tank "J" bolts, hand brake cable ends, spring "U" bolts and even exhaust clamps that you want to preserve. In use, you soak the bolt in oil, then tighten it a few turns, if you can, that leaves clear threads beneath the nut. You can now run your chaser nut right up to that nut and clear the whole track, for easy removal. Where there is room, in the case of gas tank bolts, install a coupling nut with saw cuts on both sides...removal next time will be much easier. Helps to grease those stubs and cover with a length of tubing too!