How to fix a broken antique cast iron leg?!?

Metal Shop
#1

Anyone know the best way to fix a broken cast iron leg?? This is from an old antique Murphy Bed, and the leg snapped in two during a move. I’m doing this for a friend and don’t have much experience with cast iron, but would like to give him a range of options for fixing it (which may end in me just telling him to take it to a professional because it’s a nice antique piece and I don’t want to mess it up!)

Welding cast iron can be tricky and seems like it would ruin the decorative finish. Would something as simple as using JB Weld work? Seems like that would be an easy solution, but not sure how much weight it would be able to hold.

Any and all ideas would be greatly appreciated!

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#2

If the piece is put under any kind of load brazing or welding are pretty much your only options other than some type backing plate which would drastically change looks.

If just a decorative trim piece, then something like JB weld might work, but build it up on the back where it won’t be visible, not just at the joint.

Nice looking piece metal.

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#3

You might be able to make a greensand mold of the original and cast a new replacement. We so some aluminum casting at DMS: that plus some black paint might make a suitable replacement w/out destroying the original.

#4

Nope. Cast metal shrinks from the mold size. The mold for a cast part needs to be larger the the part you end up with. For cast iron the shrinkage is about an 1/8" per foot. Doesn’t sound like much, but a 29" long leg will be nearly 5/16" shorter then the other three…

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#5

Wow… my good friend Google says Aluminum shrinks by over 6%… I suppose you could 3D scan it, clean it up, and slightly scale it up to accommodate for the shrinkage.

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#6

I thought having a reservoir where you fill the mold can provide additional metal into the mold for the part as it cools to prevent (or at least greatly reduce) the effects of shrinkage. Said reservoir above the part also provides some head pressure to help the metal flow throughout the mold.

#7

That resovoir helps to reduce voids, but it can’t do much to prevent the actual shrinkage that occurs, much of which only occurs after the material has solidified.

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#8

BITY (Brick In The Yard) has a casting product that expands a predictable amount. You might see if you can use that to make an original that is 6% larger so that the resulting cast is the correct size (or close.)

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#9

Thanks for the responses! It looks like my options are fixing the piece by brazing or welding, or casting a new piece. This seems like it would be a pretty difficult cast since it has all those open areas around the leafs and flowers, but may be fun to try nonetheless. I don’t know that I trust myself to weld on the piece without messing it up, especially since it’s a nice expensive antique.

Anyone know of a good antique restoration place that could braze or weld it back together? Or does anyone have experience with welding cast iron that would be willing to do it? I’m sure my friend would pay a reasonable fee!

#10

I don’t think any good welder would try to weld that. There just isn’t enough material to have any strength where the heat of welding alters the grain structure of the existing cast iron. If it was considered a lost cause, with minimal value, there are some things that could be tried, but I would not give them better than 25% odds of holding up even one year.

Brazing is quite likely the only way to come close to the original strength.

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#11

It would probably be a lot of work, and cost more than it’s worth…but I wonder if you could scan/3d model it and mill a new one on the HAAS, then sandblast with a large grit to give it the texture? Maybe follow up with an acid bath to help age the part?

Cast iron can be a real pain to fix, and as others have said, getting that repaired well enough to be structural will be a real trick, not something I would try on a valuable piece.

#12

You have one other option. You could get a piece of steel just a little larger than the leg and cut out all the spaces around the decorative work and also cut the piece down to the size of the leg, then use a file or grinder to shape it. Might be something that could be done on the plasma cutter.