Difficulty with silver soldering broken tooth on back gear

I did a repair on a bevel gear with all but one of it's teeth missing by building it up with brazing material and then filing it to shape. It was a bit dedious and looked like crap when it was done, but it worked. It was on the table lift of a shaper, so as long as you loosen the bolts holding the table firm before you try to crank it, it doesn't see much stress. Here's the tread:

https://www.hobby-machinist.com/threads/bevel-gear-repair.50352/#post-433389
 
I've repaired quite a few damaged/ chipped/ missing teeth on cast iron gears and if it is a broken gear that you are putting back together or for odd teeth Bronze welding is the way to go. Build up the missing area and cut a new tooth/teeth. If filing use new files. Rough shape with a thin cutting disk on a small grinder. Die grinders are good.
Trying to Silver solder cast iron parts is not a good idea. Brazing and Bronze welding are the recommended methods for cast iron repair and it is easier to make new teeth from Bronze than try and reattach a broken tooth. Oxy-Act is the way to go as the heat helps alleviate stress, a pre-heat helps with the weld as well. Several of the Bronzes are suitable.
An old Audels book on welding usually has a section on this repair. Have a look at The Internet Archive.
 
Hi Fellas. Thanks for the tips. I should have fired up the forge, but my forges are all hot enough to melt cast iron. They could be dialed down, but I just am leery of putting something that delicate into a forge. I have plenty of fire bricks, but no mounted burners. Seems like there is some more prep work to do. That suggestion about tig welding with nickel rod sounds interesting. I realize that it is easy to make a nickel arc weld non-machinable, and the more nickel you lay down, the riskier it is. But I suspect that the hybrid method with nickel tack welds and aluminum or silicon bronze tig welding might be possible. I really prefer tig welding. I have arc welded cast iron before, and this appears to be less challenging due to the geometry. Two little tacks on each side, then go to work with the bronze.
 
Would this wire work for tack welding the ends before silicon bronze brazing the replacement tooth? It is Techalloy KZ 9525-529-0443 wire nickel, chrome, iron alloy. It probably has a high melting point, but looks like a high nickel stainless. It is non-magnetic. Hmmm. I cannot seem to attach a picture. I'll try later.
 
Stick with the old way , brazing and flux then a slow Kool down wrapped in a blanket set in an oven overnight . Some use an old charcoal fire braze it after heating then place in the old coals to die and keep warm for several hours. Seems like the old way still works .
 
Hi silverbullet. You are right. I sort of wanted to come up with a new clever way making use of something I already had, but I failed. The inconel wire melts at too high of a temperature. I thought I could make a quick tack and let it cool, but by the time the filler melted, the tooth was ruined. I could lay down good bead on the flat, but small fillet welds were impossible. Also, the welds ended up being non-machinable.

I ended up putting the gear in a can of perlite with only a bit poking out and used a big propane hose torch to heat it. It worked, of course.
 
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