Correct weld for hardened steel

[ACY]

Have a hardened steel hollow shaft off an electric motor. Apparently it may be chromed on the outer surface. I want to extend a shaft from the original. I dont want to press it in, as it may expand the original outter race where the rolling bearing sits. Once placing the new shaft inside, i would like to run a weld around to hold the shafts in place. There is a double pulley load going to be placed on the new shaft, so a strong weld is required. Are there any suggestions, and/or what particular weld am i looking at?

 

[TheBlacksmith]

Welding involves melting the metals together, which will alter the hardness condition. The original shaft may become soft or brittle, depending on its composition and the amount and duration of heat applied. I think a proper interference fit may be better and if done correctly, shouldn't alter the OD.

Blacksmith

 

[Carburize]

If an interference fit is unacceptable is it possible to cut splines or keyways to join the parts together?

 

[israelkk]

You could re-machine the expanded shaft after press fitting (probably only few 0.01 mm). It may be much cheaper than welding escecially trying to keep the second part aligned correctly with the first part.

 

[strokersix]

Would an anaerobic adhesive (Loctite) and a slip fit help you?

How about drill and tap in the bottom of the hollow shaft (assuming a blind hole and soft core) and using a stud to attach the added shaft?

 

[GRoberts]

As you can see, all the posts so far point towards avoiding welding. I agree with them in that welding creates high residual stresses, and with motors, loading is normally fatigue type. This can greatly reduce the life of the shaft. If welding is done in fatigue situations, Post Weld Heat Treatment (PWHT) is normally mandatory in order to extend the life of the component.

 

[unclesyd]

I think your best bet is put a whole new shaft in the motor.
What you propose is a bad situation as there is going to be movement between the two shafts unless you can get a good/high interference fit. Even if you could correct the run-out of the two combined and welded it appears that there is going to be large load on the shaft as you move away from the bearing, this too is good as you have a metallurgical as well as a mechanical notch. One or the other or both are going to cause the shaft to fail by fatigue.

 

[ACY]

Thank all for your responses, i appreciate the feedback. The BlackSmith, unclesyd and carburize i am unaware of what an interferance fit is. It sounds as though a weld may not be suitable for this operation, and may be too stressed under load bringing the weld to failure. Alternativly if a weld is reccommended that it would suffice, i will be able to machine the extended shaft, to run true. Apparrently the hardened steel shaft is not penatrable by drill piece, which counts out drilling and placing a pin though both shafts. I am guessing that it may not be possible to be machined, if a press fit was to alter the OD. Perhaps it may take the chrome off the race where bearing sits. A keyway b/n the two shafts would stop one turning inside the other, yet not necassarily one detaching outward from inside the other.