Welding hardened steel anybody?

[Ink fabs]

Hi there i need to build up the dogs on my motorbike gearbox as it is slipping out of gear i was thinking of using 7018 rods as filler with the tig then machine back to standard spec?
I am not sure of the hardness of the gears. Or should i use a hardfacing filler wire ?
The weld is only about 8mm long. Can anybody shed some light on this?

 

[shenion]

You don't want to use 7018 as a filler for TIG. You would use ER70S-2/ A5.18 (normal mild steel filler) as it is the same.

Arc rods will not do well as TIG filler.

 

[Ink fabs]

A normal mild steel filler would soft next to a hardened steel, i still think a 7018 tig as filler would be better suited than a standard carbon steel

 

[shenion]

7018 is the same as regular mild steel filler. I still don't see why you want to use it.

 

[Delgado]

Why not just buy a suitable grade of tig rod (I'm guessing ER90 S6?) At any rate, if you try and tig with a mma electrode it wont work, or at least you'll get alot of porosity, not good if it's going to be machined after.

 

[TechnicAl]

When you dont know what the original is it makes it difficult. If its very hard you could crack it simply by heating it.

If its irreplaceable you should find out more about it

If you are prepared to risk it. I would preheat it to about 250 oC, weld it with 309L stainless and cool it very slowly. The weld will be softer (probably) but it will work harden allowing you to machine / shape it.

You could use mild steel but it will be softer and wont get any harder, still preheat etc.

Using a hard alloy will increase the chances of cracking. Make it difficult to shape after welding and it could end up harder than whatever its rubbing against and that would wear that out as well.

 

[Pete.]

You don't have to weld up the dogs, all you have to do is grind them all back the same amount to renew all the engaging faces. No sense putting heat into the gear when it's not necessary.

A simple jig would do it just fine - what tools do you have?

 

[Ink fabs]

i have a surface grinder in work with a mag base

 

[Pete.]

Perfect, so you can rough-cut the gears with a mini-grinder and get them perfect with some kind of indexing jig on the surface grinder. Set the gear up on a jig and grind all of the dogs to the same width.

If you're skilled enough with the hand grinder that's all you'd need really. I hand-ground the dogs on my xj1100 second gear when it started jumping and it worked just fine.

 

[Ink fabs]

7018 has a higher tensile strenght than a standard 6013 but was not sure about the hardness that was whay i was thinking of that grade, plus with me not know the hardness of the gear steel.
The only reason as i am trying to fix the problem in stead of just buying new part is that a gearbox rebuild could cost upto £500 !!!! money that i have not got

 

[Ink fabs]

i did think that but was not sure if the gear had been case hardened?
I am petty handy with a grinder that should be ok, i was grinding some test pieces today some 7018, 6018, , and a melted down drill just to see if i a could notice any different in the sparks, the drill seamed to be the hardest then 7018, 6013 last.
Its a rm250 2 stroke and they are known for having gearbox problems

 

[ronan]

Perfect, so you can rough-cut the gears with a mini-grinder and get them perfect with some kind of indexing jig on the surface grinder. Set the gear up on a jig and grind all of the dogs to the same width.

If you're skilled enough with the hand grinder that's all you'd need really. I hand-ground the dogs on my xj1100 second gear when it started jumping and it worked just fine.

My old 60's triumph 500 is jumping out of first gear , do you reckon it would be ok to undercut the dogs ? Triumph used straight cut gear dogs and not undercut like the japanese.