Pouring molten cast iron into a cast part


This last picture is the other side of where that broken piece fit into plsce.

A part of the support for the table on my drill press broke when I was drilling something, im not sure about this so I figured I’d ask here.

Can you cast iron into an already casted part?

I want to fill in this cavity with molten iron so this piece doesn’t break again but I’ve never heard of this being done but I suspect there’s some people on this forum with some kind of knowledge of metallurgy.

@TwistedStill @Soxhlet @cyclopath maybe @raghanded @tweedledew @Graywolf ?


Look up braze welding no idea if that’s what you’re looking for


Well that’s the obvious answer and what I’ll probably end up having to do anyways.

I was thinking of just brazing it from the inside with some silicon bronze but it’s really tight space to fit my tig torch and a pretty thin casting so I’ll have to be careful about how much heat I’m putting into it.

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I’d like to eliminate the skill from the equation and just pour molten iron into the hole if possible lol


I don’t believe it works that way unfortunately

you could use the piece with body filler as a positive and cast some new ones?

tig brazing or new castings are probably your best bet, I know there’s arc welding rods for cast iron, high nickel or something


I didn’t think so. You think I’d have some luck brazing it from the inside as best I csn and them filling that cavity with some epoxy?

I csnt imagine brazing it is gonna keep it from just breaking again from normal use. Just ginna chunk out of the casting on a different spot…

Why arc over tig for cast pieces? Or were you just throwing that out as another optuon.

just something I’ve heard of people doing, no personal experience with it. might be a little more durable but I’ve heard it’s tricky to use

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Ive heard the only welding that’s suitable for cast iron is thermal spray welding, beyond that you should braze the piece or toss it in the trash. At least those were the words said to me.

I’m just trying to get away with any easy fix, I guess I’ll just braze it.


I’ve welded cast with a mig before. Preheat the work piece and let it cool slow and it might not crack when you’re done.

I’d think brazing would be the way to go in this piece though. Maybe braze an extra backing plate inside for more support. Bust out the oxy acetylene torch for this task.


That’s what I was thinking. The silicon bronze rod I have is specifically tig rod. I think I’ll get some silicon bronze meant for acetylene and that’ll be ideal.

Ar least that way I can use flux and make it flow everywhere I need it to.

Trying to do this with tig would just bring out the worst in me… lol


Would it not be feasible to pour molten iron into the piece if I had it pre heated sufficiently?

Brazing it is only gonna be a temporary fix being that this casting really isn’t that thick.

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Maybe, but sufficient pre heat should probably be pushing orange, at least red, and nice n even. Probably easier to preheat in a kiln, but you could MacGyver it with a weed burner.

Worst case it’s a complete loss and you can make something new with your tig rig and some scrap from the local steel mart. In thinking a chunk of pipe and some imagineering.

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As far as mcguyvering I’d probably be better off just using this piece to make a mold and re casting the piece as a whole.

Just seems like a waste of effort seeing as how whats broken is just the bearing surface for what sets the angle for the table.

Such a small piece I’d hate to go thru all that effort to recreate the whole piece rather than modify what I’ve got.

No, molten iron poured into that space won’t bond and will shrink when cooled.

You can TIG weld it from one side only. How well that works depends a lot on what type of cast iron it is.

Typically a NiCr weld wire is used for cast iron repairs and the parts are preheated up to around 1200F.

Brazing with a brass filler would be easier and less prone to cracking. You can use either oxy/fuel or TIG. How much stress will the piece see?

Out of the box solution depends on what that bottom plate’s function is. Could you sandwich a machined steel plate between the casting and whatever it bolts to, so that you can just leave that broken piece out? That would let you make one perimeter weld or braze.


THIS seems like a solid approach. almost looks like a 3" triclamp lid with a hole in it would substitute. not a terribly difficult part to machine. much easier weld/braze

WHY did it fail? as in: are these sorts of forces going to be repeated, or was this a one time “damnit, why did I do that?”.


The piece that broke out is the point where the pieces bolted together.

The table support broke and fell off when was drilling through some 3/8" steel plate. I was putting down a lot of pressure but I think it was probably due to break soon anywhere by the look of those cracks growing in that threaded piece.

Tbh if it’s going to be stressed like that it seems stupid to make it out of cast instead of a steel weldment that is far less likely to crack or tear. Brazing it seems like a band aid fix and it’ll probably eventually break again in the HAZ rather than at the actual weld.

If you’ve got a descent mig welder and a friend with a lathe making a replacement doesn’t seem too difficult. I could help out with the lathe part if you’re near northern Colorado.


I’m in California but I appreciate it. I’m going to support the table with a hydraulic jack after I braze the piece back on.

Hopefully that’ll work good enough.


:100: with regular old mig. Pre-heat and slow cool the whole work piece with oxy/acetylene for a while. Don’t know why it works. Or try cast iron welding rods from tractor supply. I never tried them.