Stainless chimney cap

[MMW]

I have been asked to cut two 14" diameter holes in a large chimney cap & weld in a 2" tall ring on each hole. The holes are close to the middle of the pc which is 4.5 ft. x 5.5 ft. with a 6" lip all around. Material is 20 gauge type 304.

I have already warned the customer that it is going to warp. Any suggestions to keep warping to a minimum? In the past I have found by cutting the holes & welding in the rings it is very difficult to peen a corner weld it so it stretches back somewhat.

[WillieB]

I have been asked to cut two 14" diameter holes in a large chimney cap & weld in a 2" tall ring on each hole. The holes are close to the middle of the pc which is 4.5 ft. x 5.5 ft. with a 6" lip all around. Material is 20 gauge type 304.

I have already warned the customer that it is going to warp. Any suggestions to keep warping to a minimum? In the past I have found by cutting the holes & welding in the rings it is very difficult to peen a corner weld it so it stretches back somewhat.

[ATTACH]35184[/ATTACH]

I'm thinking out loud here. A ring welded in stainless will shrink sucking everything around it into a crumple, If you made a series of slits perpendicular to the bead of weld allowing the longer 44" weld to be 8 5-1/2" welds each could shrink affecting a smaller area. After all is cool, some hammer and dolly work makes it flatter, then fill in the slits. If you bent the slits in the flat cap up a bit into a cone first, it could shrink, pulling it all more flat.

This will be high on a chimney where the flat top will be hard to see. The outer rectangle is all you can see. I wonder if some metal stretching of the flat, not heated sheet surrounding the collars would do. Be sure your collars are big enough to be required diameter after shrinking.

[gnforge]

Stainless chimney cap

Just another thought, weld both rings on first then cut out holes.

[Meltedmetal]

Maybe put some ears on the rings or roll an angle and use rivets or spot welds? Or turn tabs up inside the holes & rivet or weld to the ring.?---Meltedmetal

[MMW]

Thanks for the replies. I was hoping for some magic idea that I haven't thought of but it is what it is.

I have decided to roll the rings with a 3/8" flange facing out. Kind of like a top hat. This will allow me to hammer & dolly the weld. I'm going to cut the holes & then weld the od of the flange onto the sheet. I will do small welds moving around & letting them cool & peening them to stretch them back out as I go.

That's the plan anyway. I'm not going to get to this for a bit due to other work but I will follow up.

[WillieB]

Have you considered solder?

[MMW]

Solder, haven't used it since high school other than sweating copper pipes. Might work for someone more skilled at it than me so alas, I will tig it.

Got the rings made tonight.

[WillieB]

My deceased neighbor was a sheet metal genius. Everything he built was self supporting with formed joints. Solder was used for sanitary reason, or to make it watertight. I never had access to the forming machines after his death. A simple solder joint is effortless once you get it clean. Use liquid flux, (clear). A big electric soldering copper, or a homemade one from a chunk of copper you heat with a propane torch work well. Wattage equates with speed. Your bead is as fast as your heat. Heat the copper, hold the copper to the joint, heat the joint, melt solder onto the copper. It'll pull to the joint. Grind the copper to a very blunt knife edge, maybe 70 degrees with a radiused edge the shape of the filet you want. A heavy filet is good as the solder doesn't have the strength of weld.

[Country Metals]

When I worked for a roofing sheet metal shop, we made 384 all stainless chimney caps for a large high end development. Some were as big as a 4x10 sheet with up to 4 holes in it.

We soldered everything. We used a propane roofing solder iron with large 1# bars (5/8" square I think). All we did was build custom wood tables to fit inside them with a flat top, use heavy steel weights to keep the ring to the sides, then use long heavy weights to keep it down. We never had a problem.

I tried to weld one and I warped it real bad.

I weld a lot of plain stainless sheet and even with my low heat pulse setting I will warp it just due to joint design and thickness.


As WillieB says, you run solder as your heat allows, but with stainless caps, at times the joint will crack immediately. Just use the rule of drywall mud. Only play with it 3 times, if it doesn't work, come back to it later.

[MMW]

Just a follow up. I got it done a while ago. Took longer than I thought but came out great. Tigged it but I think if I do something like this again I will mig it for speed. I divided up the rings into eight segments & then welded an inch in each segment, then peened, then welded another inch in each segment, then peened until I was done. Very little warpage but I did not make my rate. All in all I was satisfied though. Customer was happy also.

By rolling the rings with a flange it made it easy to peen the weld area as I went. You can see in the last pic there was very little distortion.

[ryanjones2150]

Stainless chimney cap

Did you use any copper or argon backing on those welds?

[MMW]

Did you use any copper or argon backing on those welds?

No backer or back gassing.

[walker]

Looks like you made nice work of it. I was expecting a lot more warping..