Cast iron brazing questions (with photos)

[OCJohn]

Behold the broken gear lever for the QCGB on my late model Atlas/Craftsman 12. Like to take a shot at fixing it before try finding a replacement. I’ve got a gas welding outfit and a couple different kinds of fluxed brazing rod. I did enough brazing in HS to give me courage. Also I’m cheap. So why not, right…

My question(s) – can I save myself some work and keep filler metal out of the bore by leaving a stainless dowel in the void while brazing? Am I correct to assume the brass won’t stick to the stainless and should press out after everything’s cooled? Is there a better procedure with the resources I have? Or is there a better filler metal (on Amazon) for what I’m trying to do?

WWTFD? (What would the forum do…)

 

[graham-xrf]

I binge-watched a ton of videos about repairing cast iron, and cast semi-steel. One starts with This Old Tony, and welding cast iron.

The whole range of options includes brazing with metal fillers that will wet to the iron, and fill gaps, but melt at lower temperatures than the iron, through to using nickel rods, and especially nickel-alloy rods specifically designed to match to, and repair, cast iron. I think they are the FeNiCo 65 alloy.

Your break was under tension, and is now completely open, and contaminated inside. The right way is to grind out the crack all the way to the middle, with a bevel angle, and then carefully lay in welds until it is filled. Then file out, drill and ream the hole. Folk have taken short-cuts in repairing cast iron, but putting it on a camper gas stove to keep it about 350C to 400C hot while you do the repair goes a long way to close up the temperature gradient between the weld and the iron while the fix is done. The advice is to keep heating some after the weld is done, for half a minute or so, then put the thing in a box of wood ash, covered over with ash, and leave it to cool slow. Some folk who have woodburners say the leave it in the stove overnight as it goes cold,

You can do this to leave enough of the original hole to help you re-machine the hole out. I think if you put a stainless rod in the hole, you are committing to a lower temperature filler. With enough flux in there to be effective on the iron, I am guessing you end up with a need to machine out stainless, which will be a bigger pain than fixing a hole with excess flow.

Any repair metal, joining to the iron, will make a new alloy in the metal it penetrated into, which will have new hardness, expansion coefficients, and internal tensions different to the original iron. You can definitely make effective repairs with various brazing rods. The hardball repair is to use an iron nickel cobalt alloy rod designed for it. You can get them on eBay.

 

[bill stupak]

I think the filler material will stick to SS, aluminum would be better in my opinion. You need to grind bevels in the piece have more surface area for the filler. If you've brazed before you should know to preheat the piece and let it cool slowly. Tough luck on the broken part though, I have the same lathe, fortunately I don't think there is a lot of stress on the arm when in use. You might even get away with something like JB weld, maybe.

 

[great white]

I use tig and nickle rods to weld cast.

theres a process to it, but since you don’t have tig I guess you’ll have to braze.

Or, take it to a welding shop and let them do it. That might not fit your “cheap” criteria though….

 

[matthewsx]

I've had success brazing cast iron with my gas torch, I did preheat in my BBQ and cooled slowly in kitty litter but it did stick a little. Silver solder was what was recommended by my LWS and it worked well.

Don't know about the stainless rod but why bother? You can drill/ream the part as needed after it cools. I think you'll be fine, don't over-think this, especially if you have some experience in the past.

John

 

[pontiac428]

If it's a critical part, for example a nonreplaceable one, and you want a professional repair, then using Castweld 65 nickel stick electrode under TIG would be the way to go. You'd want a bevel to fill, and you would only weld the outside to retain the bore. It would be permanent.

The silver solder you have will need some heat, but that would be my choice with oxy acetylene. Brass works too, just not quite as strong as silver.

With torch, blanket the part after the weld so it cools slowly. With resistance welding, pre-heat on the propane bbq and blanket after.

 

[lordbeezer]

Dowel would suck up a lot of your heat.

 

[C-Bag]

The last cast iron brazing job, even though I’d done a lot brazing, was the most instructive. It was a spoked cast iron hub that two of the spokes were cracked. My first attempt I V out the cracks and heated as much of the hub as possible then did my usual “buttering” of both sides of the crack then built up the braze. Not until the second crack did I seem to start getting a better flow. I had a bucket of sand that I left in the sun to warm while I did the braze. I buried the hub in the sand when done. The next day it had cracked. This time I heated the hub in my electric powder coat oven @ 500f for 20min and with an infrared thermometer I could see the heat dissipated quickly in the spokes. So I got a piece of cerro wool and after heating the oven wrapped the hub in it only exposing one spoke at a time. This time things flowed much better and when done I wrapped the hun in the cerro wool and stuck it back in the oven at 500f for 30mim, then 350 for 45min then 200 for a while then turned the oven off leaving it over night. No cracks and it’s been used many times(it’s an antique screw press) and no problems. I would not leave the pin in as I don’t think you could heat the parts good enough. YMMV.

 

[OTmachine]

You could make a new eye end to mechanically attache to the lever.
Or https://www.millerwelds.com/resources/article-library/tig-brazing-with-silicon-bronze

 

[OCJohn]

No TIG welder here.