[Bikesquid]

Just getting around to attempting some stainless steel tig and have a truly fundamental question about backers.
I've seen many of Jody's vid's discussing discoloration and using alum. or Harmful Freight's copper backers, but here's the thing....

I'm not (too) worried about backside discoloration (its just an art project) and Ain't got much aluminum block lying around but I've got a bit of mild steel that I can use as a backer, if that won't shame me.

so I'm wondering,... can I use mild steel as a backer/chill block for stainless without a side trip to "TIG-atory"?

A practical question- am I better off using nothin, or not the best idea, but in a pinch a bit-o-steel it's better than nothing.

TIG-atory - in my shop it's defined as ANY improper TIG welding resulting in more time spent fixing the result than doing it less badly the first time.

[tungstendipper]

If you use steel for a backing block it is very likely you'll weld your work to the steel blocks.

Welcome to the forum.

[Bikesquid]

If you use steel for a backing block it is very likely you'll weld your work to the steel blocks.

Welcome to the forum.

Right... so if I champfer the corner of the backer so no contact at the puddle am I off to successville or??

[tungstendipper]

By adding chamfers you are opening the backside to oxygen and sugaring can occur. It should be purged with argon. Is the a structural weld? If not you should be alright. Just move a little faster so you do not over heat the weld.

[LtBadd]

Bikesquid, what is the material thickness? If you can post a pic of what you want to weld that could be helpful.

[cj737]

You can use steel, but, you need to be careful. The steel wants to be really, really clean so as not to contaminate the stainless. Also, wrap the steel in aluminum foil (everyone has that right?) and use it to protect the stainless and perform as a backer.

It’s not som much the discoloration that should concern you (you can always clean that with a stainless brush immediately after welding) but it’s the oxidation that compromises the weld. Okay, it’s an art project and maybe it doesn’t matter, but it’s still a better practice to protect and purge the backside so your work lasts.

Pictures when you’re done, please!

[Bikesquid]

Thanks all!
It's not structural and not anything other than an excuse to get my toe in the stainless waters just an itty bitty bit. No intention of being a food services stainless welding guru... way, way more advanced than I could or want to get! Much respect for those that do deep dive into such. If it's useless or pointless I'm your guy!

This is just 1/8" plate. I'm doing this so I get myself sorted for some 18ga stainless I'll be making into a downdraft hood for behind the stove in our kitchen. Hope to get a few things sorted with this project. Like how to hold the damn right angle between plates!

Wrap with foil makes sense, thx @cj737.

Using purge gas from behind sounds like fun for the whole family! When I get to the downdraft I might just make a little purge box from some sq aluminum tube (if that's the right direction to go)...

just threw out a leaking argon hose I probably could have used that and a tee to purge the bad out, but for the timing!

[LtBadd]

I find the gas hose used for TIG machines too big in diameter (and heavy) for purging, here is my setup using the clear tubing that's very flexible available at the local big box store

Purge setup.jpg (66.47 KiB) Viewed 1814 times

[Bikesquid]

Interesting. That plus a small ball valve for the purge and I'm set. But is that hose even close to 2500psi rated? Or does it not matter? I've got a big spool of that stuff I think.

[Poland308]

Most flow regulators take the pressure down to about 50psi. It’s probably stamped on the regulator or you could check it with a second gauge.

[LtBadd]

This is a dual flowmeter I bought from USA Weld, as Josh said the regulator reduces the pressure, so the hose only sees what you set the flow meter at.

[Bikesquid]

Just wanted to post a thanks for the thoughts. (and dive just a little deeper in the backer material kiddy pool)

I did manage to find a little piece of alum angle and did a quick test weld on a little scrap of mystery stainless. The setup is a half-lap corner (a BS tech term that?!) ... meaning the top piece is about half covering the vertical piece. I'd rather line up the inside corners and squirt some filler to fill in/round over the edge

Attached the evidence. (don't look too closely at my bead, I had a seizure!)

I have to say my brain says it'll stick to the aluminum if I saturate the weld with enough heat to get full penetration, so I scooted along at a furious pace. Got close to full penetration, but as you can see, not quite.

Is that a legitimate concern or should I just take off the Depends and weld like a big boy?

Settings were approx 105amp, pulse at 35% background current, 37% on-time, and 1pps... argon at 20CFH.

[tungstendipper]

Looking good!! I'm glad you found a way.

[Poland308]

Looks good. Whether it needs to be full penetration depends on the forces it’s going to see as well as the direction the stress will be applied to it.

[Bikesquid]

Yes, but the question is IF I do full penetration will it stick to the backer?

[Poland308]

If it’s ss on an aluminum backer then it’s possible to melt through enough to get it to stick a little. But unless you really over cooked it (from the look of your beads I doubt that’s a concern) you can just bump it free with your hand.

[LtBadd]

As Josh said it could stick, but it would come loose with a light tap, other option is to run a bead from the back side.

[MarkATrombley]

Would a piece of aluminum or copper flashing between the steel backer and the stainless piece being welded be sufficient?

[p4nh4ndle]

run a bead from the back side.

Yes. This. Unless you absolutely can't get the torch inside, it's waaaay easier than trying to go full penetration without a gap or feather edge fitup (and those aren't easy to do well as a beginner either).
Let it cool in between frontside and backside passes and you shouldn't discolor too badly. Clean it with a stainless wire brush and you should be good if you did it correctly.

[HT2-4956]

Just wanted to post a thanks for the thoughts. (and dive just a little deeper in the backer material kiddy pool)

I did manage to find a little piece of alum angle and did a quick test weld on a little scrap of mystery stainless. The setup is a half-lap corner (a BS tech term that?!) ... meaning the top piece is about half covering the vertical piece. I'd rather line up the inside corners and squirt some filler to fill in/round over the edge

Attached the evidence. (don't look too closely at my bead, I had a seizure!)

I have to say my brain says it'll stick to the aluminum if I saturate the weld with enough heat to get full penetration, so I scooted along at a furious pace. Got close to full penetration, but as you can see, not quite.

Is that a legitimate concern or should I just take off the Depends and weld like a big boy?

Settings were approx 105amp, pulse at 35% background current, 37% on-time, and 1pps... argon at 20CFH.

bikesquid,

As it just so happens I did some "half lap" outside corner joints on 3/16" stainless flat bar similar to what you're doing this past week. Didn't feel the need to use any backing for how this needed to turn out. Used 1/16" filler and the "lay wire" technique to put these outside "half lap" corner fillets on. Also put a smaller fillet using the same technique on the inside.