Welding cast iron

Atlas Knife Company

Atlas Knife Company

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Feb 16, 2010
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I know, not directly knife related, but we have a lot of machinist intelligence on here and I need to tap into it. I have a Roper & Whitney #8 punch that I'm trying to modify. I drilled into it with a holesaw, only to find that it's cast iron instead of steel, and my bi-metal holesaw won't cut it. I ordered a carbide tipped holesaw, but the pilot is smaller. How can I fill the larger hole with weld so I can re-drill it with the carbide holesaw? All my previous attempts to weld cast iron have been failures, but this is a small 1/4" hole and I'm hoping I can just tack weld enough to fill it up.
 
Maybe try loading the hole with JB weld? If you can get it filled in with no air pockets it should let you get the hile saw started.

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You need a high "nickel" electrode. Graingers or McMaster should have them last I checked.
 
As ron_m80 stated, go with a nickle alloy rod. May want to pre heat the area a little before you weld the hole closed.
 
Take the old pilot bit and turn down the end to fit in the new hole saw. Even if you do not have a lathe, you can chuck the bit in a hand drill, put it in a vise and use a dremel type tool with a cut off wheel to turn it down. I often make step drill like this.
 
Alan Davis Knives said:
Take the old pilot bit and turn down the end to fit in the new hole saw. Even if you do not have a lathe, you can chuck the bit in a hand drill, put it in a vise and use a dremel type tool with a cut off wheel to turn it down. I often make step drill like this.
Click to expand...

Dovetailing that idea..... you could silver braze 1/4" round stock into the hole and re-drill it with the new pilot. Or you could braze a reducing bushing into the hole and swap your smaller pilot drill for a straight rod that fits in the bushing.

It depends on the welding process you have available.
 
I should mention that I only have a MIG welder, but I do have a spool of 308L wire I might try. Preheat with a torch and stick it in vermiculite to cool slowly.
 
You could get Nickel wire too, though I don't know if it is as machinable as high nickel rods. I doubt 308 wire will take to the cast iron, and if it does wouldn't it be a bit hard to chase with a pilot bit?

If you can pre-heat it with the torch, I would use it to silver braze a repair plug with 46% and paste flux.
 
I wouldn't weld it.

You can create more hard spots.


You have a lathe ?

just create / or buy a simple "drill bushing"
 
What's the diameter of the new drill? If you've already got a 1/4" through hole you don't need a drill to center the hole saw, you only need a centering spigot. Put a 1/4" OD tube over the drill, or take a piece of 1/4" round stock and turn the end down to fit the arbor of the new hole saw. (which you could do in your drill press with a file if you don't have a lathe.)

Depending how heavy your drill press is and how solidly you can clamp the part, you might not even need the spigot. If it's an awkward setup or a round column drill press then you probably do.
 
That 308L is only gonna make u a bigger mess. It's made to weld 308 stainless and nothing else. U want something with 99% nickel in it. Pre heat and post heat are important when welding cast. I've welded a long time and dread when someone asks me to fix something that's cast. I'd try the JB weld first IMO
 
I am a welder stick heavy plate . tap that hole and put a bolt in it cast can be unpredictable with heat applied tap it easier less risky and cheaper .drilling through a nickle weld impossible. cant stress enough you like your machine tap it !
 
I've had a problem like this at work. My solution was to cut a hole in another piece of material and clamp that on the work piece as a guide. There were no other options and it worked. Shut the naysayers mouths real quick.
 
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