The best cast iron repairs that I have seen involve meticulous cleaning, followed by placing all the pieces together in the trash bin and ordering new.

"The carbon in the cast iron will migrate to that heat zone, like little children falling into a campfire" You're analogies are impeccable, never change Tony, never change...

After  welding hundreds of cast iron parts with stick welds, the best stress reliever is a needle gun. Weld a little. Needle gun it. Weld a little. Needle gun it. From engine blocks to wash pots to machinery handles. It works. By the way Tony, I am a 70 year old machinist. I’m just another old Tony and I love watching This Old Tony.

Wait, wait.... what about bending the wet noodle?  Wouldn't that be a true test of your weld?

My family have been professional photographers for over 140 years.... your opening segment with the flash cards is the funniest thing I've ever seen! Remember though, old photographers never die... their F-stops! Rest of video was top notch as usual and answered lots of questions I had Tony. THANKS!

Almost 20 yrs ago now when i was a rig welder i asked an old guy how to weld cast iron. He said "just use 7018 rod, run it a hair hot and a hair slow". I had an old vise the mounting ears broke off so decided to try his trick. I honestly never expected it to hold very long. No preheating, drilling holes, peening, nickel rods or controlled cool down. I didn't even grind the base smooth i just wire wheeled both vise base and table to get the chunks off (again not thinking it would actually work) and sewed the base to my weld table. That vise is still welded on the table to this day. Over the years I've cut that vise no slack and beat on things in that vise with a 10 lbs sledge. Dont ask me how or why it works i just know that vise is still rock solid!
Using that trick i have also fixed many a cracked/broke cast iron manifold, never had one come back for a failed weld either. I even welded up a crack in the exhaust manifold on the same machine i was using to make the weld. He passed it on to me now I'm passing it on to all of you.

As a software developer I have no clue what's going on, but I just spent 25 minutes watching someone weld cast iron, and then another 30 mins researching how to weld cast iron.
TOT is a magical phenomenon

Man, that was a nice, sharp bend in the 1-inch square bar. I didn't realize how important WD-40 was for the process!
Seriously, thanks so much, Tony, for another brilliant video!

My father has told me several times how people would bring their cast iron to my great grandfather to weld.  After my grandfather my passed away,  I was a little shocked to find my great grandfather's welding books at the bottom of a junk box my grandfather's widow gave my family.  You can tell these books were definitely used.  These books are more prized than my signed copy of Tony La Russa's One Last Strike.

This video brings back memories of a departed friend's shop. He specialized in repairing cracked or severely damaged engine blocks. His shop had 6 large platforms for engine blocks and each platform had a box shaped kiln that lowered down onto it via small pulley arrangement. Electric elements would preheat the entire engine block and when ready, they would lift the kiln off, and he'd oxyacetylene weld the cast iron while his assistant would man a massive rosebud heating torch and a small ball-peening hammer which he'd follow the welding tapping it and post-heating it all. When all welding was complete, the kiln would be lowered back down and put on a cooldown cycle. They were lunatics and would be working in this small dark shop shirtless in winter because of the heat from everything going on. Quite a sight to behold.

My dad taught me how to stick weld cast. We had an oddball 11” pump housing on a water truck freeze and break. We dug a pit in the sand and started a huge fire and threw in the pump housing. After it sat in the coals for a while, we used a nickel welding rod on a Vantage 500 welder. We used small tack welds that we immediately peened with a ball peen hammer and kept jumping around until everything was welded. Mind you, all this was done in the hot coals. We buried the part in the coals, and buried the whole thing with hot sand. We dug it up a few days later and put it back in service. Worked fine for the next 3 years until we got rid of the truck.

The undercut on the old cast is mostly due to the temperature of the cast in relation to the arc.  The small new piece was likely at a lot higher temperature than the old bigger piece.  Because of this the lower temperature the hot tig arc will cut the colder side more then the hot side.  I know this sounds odd but keep reading.  If you were to heat up the bigger cast side with more preheat you would find it would experience far less undercutting because you could use far less amperage to weld it.  I see under cut like that all the time on 1/2in and thicker forgings I weld.  Without adequate preheat you have to run high amperage to get a proper puddle.  However the more amperage creates a wider hotter arc, which causes undercut (which is really underfill).  The under cut isn’t a issue if your using 3/32 rod and pushing a lot in or 1/8th rod, but on the piece you were welding didn’t need a weld that big therefore the undercutting would be expected due to the wider arc cone.  Without preheating the cast more one trick is to run a bit lower amperage and give the nickel time to wet out.  It’s far slower but it will reduce the undercut.  I tend to like to see nickel flow like a river more so than blast it in with high heat fast.  Steady solid heat and letting it flow is the trick.  Also I personally run big gas cups with nickel.  When the weld bead is wide and fairly liquid I want all of the super hot areas shielded, a big gas cup is the only way for this.  It will also reduce undercut potential because the toes of the weld won’t oxidize as bad, especially if you have to multi pass weld it.  👍👍

someone once told me to use stainless rods but have never tested this theory. Top Job TOT

I discovered a foolproof technique. I'll walk you through the story that led to my process.

I had a cast iron gear housing that was cracked. Bummer. So, I attempted to weld the crack closed. It cracked more. I kept going, adding more weld to each crack, grinding the excess down, inspecting, and finding a new crack. After several days and three dozen welding rods I had entirely replaced the part with nothing but weld. I imagine this will work for most people.

Tony, I know I’m a little late to getting on the comments of this video, I just want to say this real quick. You are such an inspiration and such a model in my life that I have seriously taken a completely different outlook on material and material sciences as a 21 year old. I can’t even express the appreciation that I have for not only your witty humor, but the amount of education that you provide in each of your videos. You have forever influenced me in such a way where I aspire to be a hobby machinist and fabricator. Even with a little experience I have, I itch to get my hands on any material that I can to work on. Projects like these just make me smile. Endlessly grateful for what you do, sincerely appreciate you and I hope life is treating you in the best way that it can!!

Metallurgical engineer here. Love your stuff TOT

In gray cast iron, the carbon is in flake form (think frosted flakes). These flakes have many sharp points that act as stress concentrations. Once a failure occurs on one flake, it tends to jump from sharp point to sharp point, propagating through the part. The 2 ways to mitigate the brittle characteristics are heat treating, which concentrates the carbon into spherical-ish concentrations, or treatment with magnesium (and some other chemistry details) when molten which causes the carbon to form in spheres (think cocoa puffs). The latter is cast ductile iron. These spheres do not have the same stress concentration as the flakes, making it a material that allows for some deformation before failure, with a higher ultimate tensile strength. You can also heat treat (austempering) the ductile iron to make it even stronger as well.

A good practical example to differentiate these two is taking 2 pieces of paper and cutting a couple 2d flake shape in the middle of one, and a few small circles in the middle of another. The total amount of paper removed should be about equal. Grasping the paper on each end, pull them apart. The flake shape fails rather easily, while I have seen many adult men struggle to tear the one with the circle cut. Would be a great way to demo to your boy.

Keep up the great stuff!

As a welder with 20+ years experience I feel I have to comment on this video.  



OK now that I've done that.... Thanks for the videos Tony!!  love your work

I had to weld a cast iron vise base (old Wilton 645, a little guy with too much character to let go). I did almost the same (nickel electrodes stripped of flux), but I ran the welder on AC, with the balance set at 50 percent. Just something I read on the interwebs to try out. The edge burn away was much worse doing that, so I switched to DC for the cover weld.  No preheat, and I wrapped it in a very heavy fiberglass welding blanket to cool. I also peened the hot welds. Still holding up two years later.

Oh, that was really old-school beginning :)

The flux has vitamins and minerals had me rolling.