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Repair cast iron gear teeth

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evfreek

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Discussion starter · #1 ·
Hi. I tried to repair a cast iron bull gear from a lathe which was broken by a previous owner. Since there was a tooth missing on the meshing back gear as well, it was probably broken when attempting to remove a stuck chuck. It is too easy to just lock the bull gear and engage the back gear lever to hold the spindle, but that puts all the force on one tooth of each gear, and it is just too risky.

Unfortunately, I couldn't do a decent job. The problem wasn't cracking. It was burning up the new tooth. Inconel 600 wire was used (probably not quite the correct filler). The problem is that once you get enough heat in the joint, the tip of the new tooth melts. The inconel wire melts at a much higher temperature than the cast iron, and has a high surface tension, so by the time the bead flows in, the tooth is ruined. I eventually ended up silver soldering the tooth in, and it worked just great, but I wonder how to do this with the tig. I tried practicing on some old cast iron. Everything worked fine when welding big pieces. No cracks, and a nice smooth deposit. Beads were fine as well. But, when trying to weld a small piece on to a big one, the small piece ends up getting trashed. Is this just a problem with the process? I tried to find a Youtube video, but could not. I suspect that this would also be a problem with nickel 99 wire, since the melting points are similar. I have never tried welding with higher melting point rod than the base material, so this may just be operator error. Also, it seems that silicon bronze would probably work as well, but I wanted to try a welding repair. Any suggestions? Thanks!
 
#4 ·
stevewatr said:
Might be a long shot, but what type lathe, or size gear? I have gears from a 16" south bend cone head.

Steve.

Sent from my SM-J700P using Tapatalk
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That's what I'd do. The old machine tool community are pretty cool and hobby machining forums have a lot of info. Also check Ebay.

Inconel 600 wire was used (probably not quite the correct filler).
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Everything about repairing old gear teeth was known before anyone reading this was born. You might ask Abom or Keith Fenner on Youtube how they do it. There's no point in experimenting on parts you want to save.

I'd also consider Crown Alloys cast iron MIG wire. aametalmaster's posts gave me the idea to turn my machinist bros onto it as they repair a lot of ancient cast iron meat processing equipment. They bought a roll, welded some test pieces then applied "scientific sledge hammer" testing. Now it's their go-to cast iron repair.
 
#5 ·
Bronze buildup is common, then recutting the profile. Thing about brazing is that it's less shock to the cast iron. Flows out, and bonds, at about 800 degrees. You don't have near the cracking issues you could have by trying to weld it.

Preheat the area around the broken tooth to about 500, then start brazing. When done, wrap the gear in welding blankets to allow it to cool slowly. You can also post heat to cool it down gradually before wrapping it.

Barring all that, you might be able to find a stock gear from Boston gear,, or one on Fleabay, and remachine to fit your application.

PS.......I remove stuck chuck by wedging a bar in the chuck jaws, and unlocking all the gear train, then gently rotating the chuck and bar against a block of wood on the bed. The inertia, and soft thump on the block, will generally spin 'er off.
 
#9 ·
HT2-4956 said:
That LFB (low fuming bronze) rod used for "braze welding" (like in that video) does its thing up around 1600 F.
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You're right, I got my numbers mixed up. Ought to know, been using the daylights out of the stuff lately. http://www.harrisproductsgroup.com/...sgroup.com/en/Products/Alloys/Welding/Copper-Alloy/Low-Fuming-Bronze-15-FC.aspx

Important thing is, that it's below the melting point of steel/iron. And it comes with its own safety valve.....................When the metal is getting too hot, the stuff won't flow, and starts popping. Lets you know that it might be time to go have a cigarette, and cool your heels for a bit.

It's been the go-to on my lathe restoration. I'm able to join materials without fear of burning through thin sections, build up wear surfaces, and join dissimilar metals with ease.

So far, I've had no problems with undue distortion from the heat. It seems way more forgiving than welding. As long as you control cooling, there have been no cracking issues either. I'm becoming a real fan :)
 
#10 ·
This is dating me but I have done bull gears on two lathes in the 1970's. I torch brazed making it easy to machine after and the lathes were still running in a school shop when I left. A good brazing alloy will match the strength of grey cast iron and has the bonus of being easily machinable. Dealing with the heat affected zone when machining cast iron repaired with weld is not pleasant.
 
#11 · (Edited)
Hobbytime said:
do you have access to tig? if so try 309 rod, over build the tooth then machine to shape..
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The key phrase being, "machine to shape". That stuff is HARD. A dremel/rotary-tool could assist if a mill wasn't available. Gears are not easy to cut, those type of involute gears are not straight forward to do on any mill. This is probably the reason the OP is trying to repair one.

For the application the OP mentioned in this thread, it seems the biggest danger will be having the cast iron crack. Even when pre-heating, cast iron is known to crack. Some people will say it's only a matter of time.

Is it possible to use tig with extreme pulsing to keep the heat down and not have to pre-heat, or would it most likely need to be pre-heated? IOW, can you use short bursts of high amps, with long latency in between in order to heat a small area you could build up some rod on, until the tooth was larger than full shape (i.e., to machine/shape tooth).

EDIT: Seems the best way would be to take the cast iron to about 1200-1400 degrees, slowly, before starting to tig, is that right? (or would you go higher?)

I have brazed one tooth in the past and filed it, came out ok, nothing to write home about...but that was before I had access to tig.

Alan
 
#12 ·
I replaced a missing cast iron tooth on a big music box spring-motor using regular old 70s mig. Ground it back to shape with a thin cutting wheel. It's been working for about 10 years now. Just do dabs and build up and you won't heat the cast iron up much at all.
 
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#13 ·
DougAustinTX said:
I replaced a missing cast iron tooth on a big music box spring-motor using regular old 70s mig. Ground it back to shape with a thin cutting wheel. It's been working for about 10 years now. Just do dabs and build up and you won't heat the cast iron up much at all.
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Doug,

Thanks, that is what I was curious of, if it was possible to build up rod on the missing tooth to not overheat it.

I have a similar job to take care of at some point.

I guess it couldn't hurt to pre-heat cast iron first, that was what I was curious to understand?

Alan
 
#14 ·
farmersamm said:
You're right, I got my numbers mixed up. Ought to know, been using the daylights out of the stuff lately. http://www.harrisproductsgroup.com/...sgroup.com/en/Products/Alloys/Welding/Copper-Alloy/Low-Fuming-Bronze-15-FC.aspx

Important thing is, that it's below the melting point of steel/iron. And it comes with its own safety valve.....................When the metal is getting too hot, the stuff won't flow, and starts popping. Lets you know that it might be time to go have a cigarette, and cool your heels for a bit.

It's been the go-to on my lathe restoration. I'm able to join materials without fear of burning through thin sections, build up wear surfaces, and join dissimilar metals with ease.

So far, I've had no problems with undue distortion from the heat. It seems way more forgiving than welding. As long as you control cooling, there have been no cracking issues either. I'm becoming a real fan :)
Click to expand...
As far as controlled (slow) cooling goes....I never do it and have never had anything crack. I just let it sit on the bench and cool off in still (no fan) air. With Bronze Brazing there's not a problematic "HAZ" like there would be if you melted into the cast with arc welding.

Also, there's two main types of rod. There's regular LFB and LFB-15. The 15 works up around 1700 F. (as opposed to in the neighborhood of 1600 F. for regular LFB). The "15" type is not as fluid as the other and works better for "build up" situations.
 
#15 ·
TraditionalToolworks said:
The key phrase being, "machine to shape". That stuff is HARD. A dremel/rotary-tool could assist if a mill wasn't available. Gears are not easy to cut, those type of involute gears are not straight forward to do on any mill. This is probably the reason the OP is trying to repair one.

For the application the OP mentioned in this thread, it seems the biggest danger will be having the cast iron crack. Even when pre-heating, cast iron is known to crack. Some people will say it's only a matter of time.

Is it possible to use tig with extreme pulsing to keep the heat down and not have to pre-heat, or would it most likely need to be pre-heated? IOW, can you use short bursts of high amps, with long latency in between in order to heat a small area you could build up some rod on, until the tooth was larger than full shape (i.e., to machine/shape tooth).

EDIT: Seems the best way would be to take the cast iron to about 1200-1400 degrees, slowly, before starting to tig, is that right? (or would you go higher?)

I have brazed one tooth in the past and filed it, came out ok, nothing to write home about...but that was before I had access to tig.

Alan
Click to expand...
I have repaired several cast item items and exhaust manifolds with preheat of items then tig with 309 and then cover or bury in sand to cool down, granted none had to be machined so the filler was picked more on resistance to crack, I wouldt have assumed braze was strong enough to make gear teeth from but after seeing a few videos and responses I will have a new respect for what it can be used for..
 
Discussion starter · #17 ·
Hi farmersamm. The suggestion to use low fuming bronze sounds like just what I need. I was hoping to weld it, but it's looking too tricky. I have an oxy fuel torch and a tig welder, so this should be good.
 
#18 ·
I've repaired more than a few cast iron things for people over the years and its just never been a "mistake" to go with Bronze Brazing. Any kind of arc welding on the other hand well, let's just say I mostly ended up wishing I'd of never tried it.
 
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