[How do I?] Repair Cast Iron

If you weld spread the welds around do not just weld straight across. Weld 1/2" -1" then skip to a different spot. As mentioned above Pre/Post heat are a must.
Mark
 
Clamp it good pre heat it on the grill, Keep in kitty litter for a day to cool down . Make a plate to support the bottom after you fly cut the deck it should be good to go.
 
Find people who heat with wood and get 2 or 3 big tubs of wood ashes. When welding is done cover as deep as possible with wood ashes. Nothing better for slow cooling. A couple days for a part that size. Also the slow very hot preheating important also. Cast iron is VERY high in carbon content. All that carbon tries to go to your weld puddle. This results in a very brittle area at the edge of your weld. As the part cools, the carbon tries to return where it came from. If it tries to go back quick by rapid cooling the part will stress crack at the edge of the weld, usually full length of the weld bead. All the info on the vee out , and etc. is pretty much good info. I would definately go with the bolt on plate after machining.
 
The original question is about welding and welding CI has always scared the daylights out of me. Trying to weld it yourself if you have to ask for guidance might end up making it unweldable thereafter even for a pro. If the purpose is to save the press, I would consider having it done by a pro. No offence intended but I don't want you to loose a press and a friend.
Also, about the epoxy option if it ever comes to that, there are many different kinds of epoxies and I would only choose an epoxy formulated for this specific purpose. With respect.
 
Thanks for all the great advice. I'll definitely vee out the crack and pre/post heat. I like the idea of adding a substantial plate
base.

I found the following link that gives a good summary of the available welding options: http://mewelding.com/cast-iron/

Since it was "pre-broken" my friend got it for almost nothing (<$5) and has low expectations for it a failure will no endanger our friendship.

It looks to be a 2-ton press so the maximum stress on one leg will be about 2000 lbs. There are about 2 sq inches of joining surface so 1000 psi does not look too challenging. This ignores the fact that the stress will be non-uniform so the actual join will need to be significantly stronger than 1000 psi. It does tell me that the important thing is not the joint itself but avoiding stress cracking.

I am leaning towards trying the silicon bronze mig process in part because the preheat requirements look to be less demanding.
I still have not found any end user reports of how well it works.

I'll have to get some charcoal and rig up something for a preheat "oven" so it will proably be next week before I make the attempt. I'll report back on how it goes.
 
A lot can be accomplished with good preheating. I fixed a vise base by arc welding it. The vise was on the side of the road with a free sign on it. I buried it in loose gravel and left the crack showing, after generously vee'ing it out. I then heated it with a big propane torch until it was at least 1000 degrees F. It was then welded with 6011, since nickel rod was too expensive for a low return repair like this. Every bead I laid down was peened heavily with a ball peen hammer. Almost hard enough to crack the original cast iron (tried while cold). If it cracks, it wasn't meant to be repaired. Then another bead. Then more peening. The peening helps to spread the bead and relieve the shrinkage in the HAZ. Besides, blacksmiths enjoy doing it. When it was all done, the open area was filled in with already heated gravel, and the whole mess left to cool overnight. The weld turned out to be strong enough and withstood more pounding until I sold the vise on craigslist to make room for a larger upgrade.

One of the saddest things I have seen is a Fisher anvil with a steel top welded to a cast iron base that was repaired with about 5 pounds of Ni rod. The repair failed, and the top came up on one side. Remember: pouring a lot of nickel into a job means you have a lot of skin in the game. Better make real sure of yourself. If it was me, I'd have done the weld with regular steel rod like 7018 with heavy preheat on the base of the anvil and a wet rag on the top. Something like this may almost be worth springing for one tempilstik. But not several pounds of nickel rod.
 
I was able to get back to this this weekend. I decided to try MIG brazing with silicon bronze wire. I ran some test/practice beads on scrap steel and they went down very smooth. I vee'd out both sides of the crack, preheated the casting to about 500 F and had at it. The arc was unstable and there was a lot of spatter. The result was so ugly that I am a little embarrassed to show it here but this forum is for sharing/learning so here is the result:
arbor-press-fix.jpg
After slow cooling and inspection I was a little more optimistic. There was no sign of cracking and the bronze adhered well to the cast iron, so well that I had to grind off some of the bb's. I reassembled it and it held up to cranking on a 4-ft cheater bar as hard as I could. Time will tell.
 
Looks pretty good. My HF Portapower broke the alligator jaw a couple of weeks ago. I couldn't get it to hold heat very well & when the rod did melt it just beaded instead of running. I got tired of messing with it & just flux core welded it. It didn't hold of course.
 
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