Explain This if You Can

I welded something successfully today, and I can’t figure out why it worked.

I bought a motor on Ebay. It had a cast iron base. The seller packed it badly, and the possibly resentful USPS people who handled it broke a foot off of it. I got a full refund, but I didn’t have to surrender the motor, and I haven’t found anyone who wants to buy it.

I looked into ways to put the broken bit back on. Ordinarily, people braze cast iron. It’s considered very difficult to weld (adding steel filler to it with high heat), because cast iron expands and contracts differently than welding wire, and the welds tend to pop as the work cools. To braze, you have to heat the part to something like 400 degrees. Then you melt bronze (I think) into it with a torch, and you cover the whole mess with welding blankets while it cools.

No way could I braze this thing, because if you heat a motor to 400 degrees, the windings melt.

You can also TIG weld it, but I don’t have a TIG welder.

I found some guy on the web claiming you can MIG weld cast iron with only a slight preheat–about 100 degrees–using non-magnetic stainless wire. You then “peen” the welds with a hammer or needle scaler to somehow or other counteract the problem with the welds opening. Maybe it expands the weld material horizontally.

It sounded nuts, but I asked around and couldn’t find a better idea, so I decided to try it.

Today I cut shallow v-grooves in the places where the parts met (standard when welding thick parts), and I cleaned them with alcohol to make sure there was no loose graphite on them. Cast iron is full of graphite, and supposedly it contaminates weld filler and causes problems.

I clamped the parts together with a Bessey clamp knockoff and started welding. Naturally I forgot to turn on the gas. The first two tacks were giant blobs that looked like sponges. I ground them down to start over, but I didn’t get all the crap out. Oddly, the welds held, and I was able to remove the clamp.

Someone on the web suggested using high wire feed. That was bad advice. Even after I turned the gas on, the wire spewed into the welds and made more blobs. I turned the feed down, but I never got it low enough to be controllable.

I also had trouble with my mask. I don’t think it darkened at all on the first two welds. I had to adjust it to the darkest level in order to see anything.

I continued making very small welds, peening, and waiting. That’s part of the technique.

When cast iron welds fail, they make a sound like “tink.” I never heard that sound. That surprised me, because what I was doing was sort of a Hail Mary job. I didn’t think it would work.

I got it welded up, and then I spent about ten years cleaning it up with the angle grinder and a rotary tool. A bolt has to go through the motor base, and that means a washer has to sit flat on top of it. The base will sit on a platform, so it has to be flat on the bottom.

Everything went fine, apart from welding very clumsily and making a mess. When it was done, I beat the part with the hammer’s handle, and I tried to pull it loose with my hands. I couldn’t budge it. I think it’s actually welded. It’s probably a D on a scale of A to F, but it’s not going to be under much stress. Maybe it’s not good enough, but I can tell you this: there is no way in hell I’m going to redo it until it fails again.

Because the weld didn’t fail, I’m not sure if I learned anything about welding cast iron. If it had failed, I would have known the method didn’t work. Because it doesn’t appear to have failed, I’m not sure what’s happening. Sometimes really bad welds seem acceptable at first.

Here’s something weird that appears to be true: it seems like it’s possible to weld stainless directly to cast iron, and that would mean it’s possible to build up stainless weld on a cast part. If that’s true, you should be able to coat one side of a part with stainless weld, make a stainless replacement for the other piece, and weld it to the congealed filler. If my weld fails, I plan to try that. Can’t hurt. Hey, it’s a free motor.

I don’t know what to do with the motor. I now have three pretty good motors sitting around doing nothing. The one I fixed is really nice. Maybe I could try to build a 6×48 belt sander. I don’t really need one, but they’re great tools to have. It would be nice to build one and have a disk sander on the side.

I wish I had some cast iron scrap. I’d practice welding it to see if my results could be trusted.

Also, it would be nice to improve the appearance of my welds. When I weld, all I see is arc glare and red metal. It’s blind luck if I hit the joint.

Here’s a photo. It may not look like it, but the welded-on part is aligned perfectly.