Hello. Tigging 1/2" square tube?

Cory · Tue Jun 16, 2020 6:27 pm

Hello Everyone,

My name is Cory, I work as an artist designing and building custom lighting, furniture, and sculpture, mostly in metal.

My latest project is a ceiling fixture built on a frame of 1/2" square steel tubing which also contains the electrical. There are a number of "T" and miter joints that need to be very clean. It will have a blackened finish, not paint. My experience in welding has been MIG, as well as some silver and lead soldering, and so I tried some sample pieces with bronze brazing. They turned out quite nice visually, and held up under strength testing, so I committed to the actual piece which is a bit more complex with numerous criss-crossed joints. Again, things looked good until I did a strength test where nearly half of the joints failed. Not a happy moment, and I do not know what went wrong.

Starting over, I am considering TIG, and began researching various videos to that effect which is how I ended up here, having really enjoyed Jody's video style at weldingtipsandtricks. I need to effectively build this fixture so that it doesn't fall apart. Perhaps I am being too optimistic about learning to TIG quickly to pull it off, but I really don't know. I watched a couple of videos with helpful information, but would really appreciate hearing anything from any of you to help me along.

I would post some pictures, but nothing happens when I click on the little "Img" square at the top. Any help with that too would be appreciated.
Thanks.

Oscar · Tue Jun 16, 2020 8:34 pm

Cory wrote: but would really appreciate hearing anything from any of you to help me along.

Welcome. I'm sure when you have enough details about the actual project you'll be able to get lots of answers.

The "img" button is used to hot-link pictures stored off-site on [typically] photo-hosting sites/servers. The text that goes between the img tags in brackets is the URL to the actual picture .png, .bmp, .jpg, .jpeg, or any other permissible photo file type that is compatible with this forum software.

Spartan · Tue Jun 16, 2020 8:50 pm

Sounds like an interesting project. Brazing won't take a black oxide finish well (if that is the direction which you were going, which it sounded like...but maybe you were intending a powder coat or something else). I'm a bit surprised it failed, though. You must have really womped on it during the stress test.

TIG is probably the way to go, but also keep in mind the benefit of grinding/sanding the welds smooth for decorative pieces, so perhaps the chosen welding process may not be too critical, but of course only you know whether or not that is true.

Good luck, and looking forward to seeing some pics.

TraditionalToolworks · Tue Jun 16, 2020 9:38 pm

I have used Oxpho-Blue on tube I have tig welded, after I have welded it. It does darken the weld, but is a slightly different color, not to be surprised over. I think it is totally acceptable. So, you can apply it to the weld, if that was your concern. I was using carbon steel tube with ER70S-2 filler.

v5cvbb · Tue Jun 16, 2020 10:25 pm

Brazing is pretty strong from what little I've done. I'd like to see that failure.

BillE.Dee · Wed Jun 17, 2020 7:01 am

Hello Cory and welcome. The bronze brazing is right up close to a welded joint and I don't understand what failed when you tested the joints. You didn't mention if you really cleaned the joints so the braze could hold on to the piece. Are you using the bronze for a special effect or some other reason instead of welding? Also, like Spartan stated ,, the bronze won't take the blackening very well as the rest of the structure...so I'm guessing you are using it for a different look. Hope to see some pictures...
gramps.

Cory · Wed Jun 17, 2020 10:53 am

Here is more info in response to several questions:
1. Cleaning: the joints were cut dry on a band saw, filed, and wire wheeled. I applied a flux. No chemical though.
2. Why bronze? I though there would be less clean up and distortion than my previous experience with MIG welding. I realize it does not take the patina, but thought the hairline color was acceptable and of some visual interest as the 6 shade heads are made in bronze, so there would be a bit of a relationship there.
3. Did I really "whomp" the strength test? My initial sample pieces I put in the vise and heaved up on them by hand. The tubing bent, but the join did not break. I'm no Hercules, and the test on the actual parts I broke by hand without the vise. Same prep as the samples.

I am attempting to attach some pics of the failed joints, my initial setup, a crude model of the fixture, and a full scale mock up in wood of what I am trying to build. The table in the model of the entire room (we have already built the real one) is made of 1/4" bronze plate with a 5" walnut top.
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