# Repairs to cast iron



## Izzy (Jan 18, 2017)

I have a few cast iron parts that I would like to attempt repairing. I have little experience working with cast iron and I'm not sure what method would be best for repairing certain parts.
I've got 2 things I need repaired 
1. Is a cast iron cover that broke in half it is a clean brake though and fits together nicely 
2. I have a few gears that need a new tooth or 2 
So what method would u guys recommend for each part and why? I'm just trying to learn so the more info the better! Also if anyone has any links to some guides for the method recommended that would be great to!


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## RJSakowski (Jan 18, 2017)

Disclaimer: I'm no expert at welding  cast.  My two cents:  

You can weld or braze cast iron. Cast iron comes in various forms.  White cast is commonly used for decorative pieces and cookware.  It is called white because a fresh break looks silvering color.  The large percentage of carbon in the cast makes it brittle and, in my experience, difficult to weld.  The repair usually breaks adjacent to the weld.  Brazing will work on it.  Grey cast is white cast iron that has been heat treated, much like annealing carbon steel.  It is somewhat ductile and will weld with proper technique.  Nickle rod is often used to weld cast as it is ductile and a better match for thermal expansion coefficient.  Even so, a common practice is to peen the nickle weld immediately after laying a bead to physically expand the weld to relieve some of the tension in the cooling cast.  For very simple welds, I have successfully welded cast with mild steel rod.  The weld area was small and not subject to a large amount of thermal stresses as the weld cooled.  Welding studs into an exhaust manifold come to mind.

I guess that I would try brazing in both your examples.  After brazing, I would heat the entire work to something short of the brazing temperature and cool it slowly in a bed of ashes.  This will tend to minimize any hardening which may have occurred during the repair process.


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## brino (Jan 18, 2017)

Hi Izzy,

Lots of info here:
http://www.hobby-machinist.com/threads/welding-cast-iron.42577/
I read that whole thread before doing my own repair:
http://www.hobby-machinist.com/threads/found-a-sheet-metal-shear-that-needed-a-small-repair.48881/

I decided to braze with ox-acetylene, my basic method was:
1) grind a vee shape deep enough for penetration, but leaving a clean edge for alignment of the pieces
2) work from one end and move along the crack filling as you go, do not worry about adding too much material
3) grind down the bumps that are too high, fill any spots to low, repeat step 3 as required

Here's a Keith Rucker video where he replaces a missing gear tooth by brazing in material and then re cutting the gaps.





-brino


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## f350ca (Jan 18, 2017)

Pretty much what RJ said, again Im not an expert but have had good luck in most cases.
For the covers if they're thin I'd braze them. 
I preheat the cast with a propane weed burner, big flame so you get an even heating. Preheat seams to reduce the stress from the weld shrinking, then cool slowly. 
If stick welding I use an alloy for cast iron and as said peen the heck out of it with a dull welding hammer. Short maybe inch long welds, one at a time then fill in.
Groove the joint out with a carbide burr, I've read a grinding disk leaves traces of the wheel in the weld and can affect it. Don't know I use a burr.

Greg


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## Izzy (Jan 18, 2017)

Thanks guys I was hesitant to go down the welding path I've welded cast iron manifolds in the past but didn't have much luck (they cracked again a month later) and I've never brazed before at all so I wasn't sure if that would be sufficient for what I'm doing. All I have is a MIG welder so I'll have to bust out the torches and give it a go!


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## chips&more (Jan 18, 2017)

Are the repairs to expensive parts? Welding/brazing cast iron is not a walk in the park, things can go wrong fast! I understand your eagerness for a challenge. But, if things go wrong, will the parts be too hard to replace? Maybe find someone with a good back ground in welding cast iron. It might be cheaper in the long run…Dave.


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## Izzy (Jan 18, 2017)

It's for the McKenzie lathe I have, the company doesn't exist anymore so parts availability is 0 lol I've never brazed but I've torch soughtered and I'm pretty good with an oxy/acet torch. I've tried finding someone around here who has do e this before so I could get some tips but can't find anyone. It's a bit of a dying art I guess and part of the reason id like to learn myself. The way I look at it is the part is already broken so it's not like it could get any worse either the brazing works and I have a fixed part or it doesn't work and I'm left with what I started with, no biggie. I gonna give it a shot though just gotta prep the material get some flux and some ni99 rod (correct me if I'm wrong) and I should be good I also have a needle scaler for peening   thanks to @brino for the idea!


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## Izzy (Jan 18, 2017)

This is the part its just a cover for the change gears absolute worst case scenario I could live without it or just the top half lol


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## f350ca (Jan 18, 2017)

Izzy, the NI99 rod is for stick welding, if your looking at welding it with the torch all you need is brazing rod. Don't think it needs to be peened, at least I've never. I'd preheat the whole part to 4 or 500 f with a propane torch first, but may not be necessary.

Greg


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## Eddyde (Jan 18, 2017)

I have stick welded Cast Iron several times but I'm no expert. I pre heat, peen, weld short beads and allow it to cool slowly. Most times I had very good results but on a couple of castings I had to weld more cracks that formed from the welding than the original repair...


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## brino (Jan 18, 2017)

Izzy said:


> The way I look at it is the part is already broken so it's not like it could get any worse either the brazing works and I have a fixed part or it doesn't work and I'm left with what I started with, no biggie.



I think brazing is the way to go. If something goes wrong (misalignment or whatever) just reheat, knock/shake the brazing material off, and try again. Worst case you have some extra bronze colour on it, but that can be ground and painted over.



Izzy said:


> I gonna give it a shot though just gotta prep the material get some flux and some ni99 rod (correct me if I'm wrong)



As Greg said, just bronze brazing rod for brazing. Many (most?) come with a flux coating.

I believe that the higher temperature of welding greatly increase the risk of cracking on cooling (thermal expansion/contraction stress).

That cover looks thin, is there enough clearance on the back that you could braze a couple small rods or short pieces of small dia. all-thread back there? It might add some extra support/strength.

-brino


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## Ulma Doctor (Jan 18, 2017)

to echo others...
if you are going to repair, brazing is the way to go.
coated LFB (low fuming bronze)

Why? because is very convenient, relatively inexpensive and is suitable for use in these repairs.

on the cover:
if you can, dress the fracture on both sides to somewhere around a 45* angle and reassemble
add supports and clamp it up to keep alignment of sections
braze the areas and remove clamping elements as soon as possible
allow the assembly to cool slowly

on the gear:
i'd construct a gear tooth blank from steel or cast iron
cut out bad tooth
insert blank, and braze into place
let cool slowly
re-cut tooth profile, (this could be done with diligence and a file)
an angle grinder could speed up the forming process, so that less milling could be required if the gear teeth are large

i wish you the best of luck in the repairs


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## roadie33 (Jan 19, 2017)

Preheat to 400. Use good rod and plenty of flux. After you are done brazing it, wrap it in a fireproof welding blanket and let it cool slowly over night. Next day grind off and smooth out the excess and you should be good to go.


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## Izzy (Jan 19, 2017)

@Ulma Doctor when you say gear tooth blank do you mean cut a tooth into a piece of metal then braze that tooth onto the gear? I never thought of that and I also didn't know it could be done with a file! Which is great to hear since my machines are still down until spring time at the earliest...
@brino that's a good idea and i may have just the perfect piece of scrap in mind to go in that spot!


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## Ulma Doctor (Jan 19, 2017)

Izzy said:


> @Ulma Doctor when you say gear tooth blank do you mean cut a tooth into a piece of metal then braze that tooth onto the gear? I never thought of that and I also didn't know it could be done with a file! Which is great to hear since my machines are still down until spring time at the earliest...



 Hi Izzy,
yes sir, that is exactly what i mean.
you can produce a tooth blank and braze it into position.
the machining (filing) generally follows that step to keep the position of the gear tooth contact correct, should the tooth may be leaning to one side or the other

it will be a time consuming process, but it is completely doable


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## Glenn Brooks (Jan 19, 2017)

Hi Doc,  Iam a real fan of sending this kind of work out to a fellow here in Washington that specializes in repairing cast iron parts.   You could call Cast Iron Repair, in Smokey Point, Washington.  Might  actually be Burlington, WA in the phone book. The owners name is Mike.  Here is his phone number:  360.657.7660. He has been doing cast iron welding exclusively since the late 1960's and really knows his stuff.  Last guy doing this west of the Mississippi I've heard.

you will have some significant risks with brazing.  Mainly, if you use to much heat, or to concentrated a flame, you will burn through the edges of the parts.  Cast iron melts like butter when you exceed the heat threshold, and big worm holes ensure.  So watch your flame, carefully. 

Second thing, you must absolutely clean up the edges, so you are dealing with fresh cast iron - sand blasting clean is best. 

also, cast iron cracks after 'welding' because often people don't use enuf preheat, OR post- heat.  So, you  will need to bring the whole piece up to cherry red heat and hold it at that temp for more than 15 minutes. Half hour might be better.  Then after completing your operation, hold the part at post heat red for another 15-30 minutes, then keeping it hot, very gradually cool down by wrapping in the fire blanket method, or burying completely in hot sand,  overnight. 

The ideal method for heating is to use two weed burners, one on each side of the part, with the heat reflected back into the part by a simple three sided fire block furnance, open on the front end, but closed on the bottom, right and left, and back sides. Cracking happens due to inconsistent heating and improper cooling, where the granular structure cools inconsistently - producing internal stresses that eventually - crack.  This is a very slow process compared to any kind of stick or tig work on mild steeel.  using two burners and a simple fire brick furnance, plus extended cooling down, will really mitigate those internal stresses, and greatly reduce cracking.

As others above have mentioned, Brazing is OK for closing up small cracks and filling voids. but the proper way is to fill and weld the broken area with a similar iron filler.

If you decide  not to go through with brazing yourself, you could send Mike the parts via UPS flat rate and he likely will return them to you same way in under two weeks. At least that is my experience.   ive taken him five different cast iron parts off machine tools and have had superb results, every time.  As you can tell, Iam a big fan.  Mike has fixed everything from machine tool castings to piecing back together fractured and broken engine blocks.  One was a $15 Mill antique 1930's race car motor - Bugatti or similar-  that someone forgot to drain the water out of.  The engine froze and cracked into three or four pieces one winter. As it was irreplaceable, the owners sent Mike the bits and pieces and he returned a functioning motor to them.  For  the small stuff I've taken him, usually I can't tell where the break was when I pick up the repaired part.  Sometimes, as in welding through a dovetail, or making a tooth in a gear, you will need to machine out excess filler from around the repair. but with cast iron there is no heat hardening of the material, and the iron machines readily.   So anyway, highly recommended.  BTW usually he charges me $100 for the kind of work you described in your first post.  Last piece was $200, but involved a bit more set up and the afore mentioned dove tail repair meant  welding and filling through both sides of a larger rectangular broken 3 HP motor motor mount, that broke along the dovetail after a horizontal mill fell over.  So more shop time.  Anyway, the plate now looks good as new.  Iam confident he would repair your parts to as new condition, should you decide to send to him.

Regards
Glenn


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## brino (Jan 19, 2017)

Ulma Doctor said:


> i'd construct a gear tooth blank from steel or cast iron, cut out bad tooth, insert blank, and braze into place





Izzy said:


> when you say gear tooth blank do you mean cut a tooth into a piece of metal then braze that tooth onto the gear?



Keith Rucker also has a two-part video on adding a gear tooth:








-the idea is the same, though probably on a larger scale,
-he uses other machine tools to do it!

-brino


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## Izzy (Jan 19, 2017)

I actually haven't seen that video yet! I honestly wouldn't have known that would be an option. I guess at this point it might be easier to do that as I could trace the tooth off another gear and make sure they're relatively the same before brazing. 
I gotta say this forum really inspires greatness and I probably wouldn't have the ambition or even known how to try this myself if it wasn't for all the positive responses I've gotten from the group thanks alot guys I'll post up some results as soon as I give it a shot!


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## Izzy (Jan 26, 2017)

Soo here's what I got, its not very pretty but the 2 pieces are stuck together lol 
I'm gonna grind a V down to the braze from the other side and get a little more practice in before I attempt brazing any gear teeth or the steady rest...


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## Izzy (Jan 26, 2017)

Getting a little better...


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## f350ca (Jan 26, 2017)

Getting much better as you go Izzy. Haven't tried it yet, haven't brazed anything in a while but read somewhere to use the paste silver solder flux on the weld area with the flux cover rod. Makes sense.

Greg


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## Ulma Doctor (Jan 26, 2017)

looking good Izzy!
i knew you could do anything you put your mind to!


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## Mister Ed (Jan 26, 2017)

Glenn Brooks said:


> As others above have mentioned, Brazing is OK for closing up small cracks and filling voids. but the proper way is to fill and weld the broken area with a similar iron filler.


I hate to say it but I have had 8' windmill wheel hubs that were broken in half (radially) brazed back together and they hold up fine in the wind.


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## Izzy (Jan 26, 2017)

Thanks! Ive learned alot the past few months and got the confidence boost I needed to start tackling bigger projects, like the steady rest! I honestly thought it was too broken to repair but I'm glad I collected the pieces! If all goes well on the steady rest brazing I'll braze the gears. Good thing the shop is slow and I can work on my own projects


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