Weld repair to gear

[nutwood]

This isn't really a car question but I reckon the expertise on this site will know the answer. I've broken a tooth off a bevel gear in the front of a tractor. It's a 4wd tractor and the gear is on the outer end of one axle. It turns the drive through a right angle bend as the wheels are offset down.
Anyway I had this broken tooth and it's going to take months to get another axle so I've carefully rebuilt the tooth with my trusty stick welder and low hydrogen rods (Austarc 16TC). I heated the gear up first with the oxy and after I ground it to match the rest, I heated it all up again.
Hopefully there's no stresses left but I've now got a "soft" gear and axle end.
There's no hope that my angle ground and filed gear is perfect, so my question is; am I better off leaving it soft so it'll wear in to the other gear or should I re-temper the axle on the basis that my tooth will still be softer and I'm not risking breaking the axle.
I will be replacing both gears as soon as I can get my hands on parts but it's being a problem just now and a three wheeled tractor is no use!
Interested if anyone else has done such a repair and how it turned out.

[no1200]

Your sort of stuck. Because the gear will be induction hardened, only hardened for 20thou or so and it's difficult to replicate. I would weld without heating using dissimilar rods, check dimensions and reinstall while waiting for new parts. You will never remake the component at home as good as new. What tractor is it?

[nutwood]

Hmmm, that's a point. Still if the gear was originally only surface hardened, that hardening's long gone as there's a lot of wear on the original teeth. That's one of the reasons I'm replacing the lot.
I'm thinking I might fully anneal it, then reheat and oil quench. My concern is that the gear is part of the axle and I don't want to screw up the axle strength any more than I already have. It's an interesting exercise anyway!
It's a Belarus tractor and I usually get my parts straight from the Ukraine. Possible I might hunt up a SH axle around the place but from the wear on mine, I doubt it's worth it.

[da9jeff]

is this your daily driver? :D

[nutwood]

Yes.

[curmudgeon]

I'd be inclined to just bung it in as is. Then drive it as gently as possible and hope it lasts until the replacements turn up. You might improve it with further heat treatment but it's hard to get good, predictable results without knowing the steel composition and only having basic equipment. It's easy to end up with brittle sections if all you have is a heating tip and a bucket..
I've done similar repairs (on drill rigs not tractors) and they have held up well enough to keep going until new bits were on hand. I wouldn't expect to get months out of it though..

[bigmuz]

If it is a straight bevel then you have a chance of it being ok I reckon.

If it is hypoid then forget it.

[nutwood]

That's my concern with treating it. At least it's all relaxed at the moment, if a little weak. However it's possible that I might be able to do a good job of the treatment as I'm currently overhauling a furnace at a spring works. It's very tempting to toss my axle into their process and see what eventuates.
Did you have any failures with your drill rig repairs? To me the weld is softer than the rest of the gear, I can tell that when I'm filing it, but if I do nothing and simply put it in, all that'll happen is it'll wear fast.
If I heat treat and get it wrong, the axle will break although if I get it right, the weld will be that much harder.
The other scenario might be that the whole new tooth just fractures away from the gear? Not sure what to do to prevent that. Perhaps a thorough annealing prior to a mild hardening?

[nutwood]

Straight bevel.

[curmudgeon]

No, they didn't fail but then I didn't run them for any longer than a week or two at the most. The fact that you have access to the spring furnace (and I'm also assuming people with heat treatment expertise) changes things a bit, so if these guys are confident it might be worth a go. I'd lean towards the less hard/less brittle side though. The reason I originally leant towards leaving it as is that if the new tooth wears you can always build it up again but if something breaks because of poor HT you might be without the use of the tractor.

[no1200]

if you do a full penetrant heat in a spring furnance the axle will break under loading, wrong style of treatment. weld and leave it be till the parts turn up. If it's only one tooth on a crown it'll be right, hypoid or not:)

[Gammaboy]

Case hardening is the process you want.

[nutwood]

Just a follow up to this thread that I stated regarding my broken tractor gear. I repaired it as per above; heated up and then built up the tooth with 16TC rods. I then put some time in with an angle grinder and a file to get the tooth as near as I could to the others. I then reinstalled in tractor and forgot about it as I ran into grief getting a replacement part.
That was in February. Yesterday I pulled the cover off to have a look. I can't tell which tooth it was! All is in perfect order and the tractor's done a lot of work since I did the repair.
It's probably not the thing for a high performance gear box but I thought the feedback would be interesting to anyone else with a similar problem.

[GTSBoy]

That's a good result.

Mind you, having worked in the part of the world where that tractor was built, I wouldn't be surprised to know that they built the gears up from scratch by stick welding each one onto a bare hub anyway!!

[nutwood]

Thanks for that GTS, you've made my day. You don't (actually, obviously you do!) know just how true that is!!