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Old 12th August 2017, 02:18 AM   #1
Cliffbeer2
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Stainless mig welding a custom exhaust system

Just wondering if I should tackle welding up a custom stainless exhaust system (downstream of the 4-into-1 manifold and collector) for my bastardized Lotus Esprit project (with a SBF).

I'm a decent mig welder with mild steel - good penetration, strong welds, not the prettiest looking welds but not bad. I have a Miller 140 and it does a decent job even though it's not 220V.

Now, I've never welded stainless before, and I imagine it's more difficult. If I use some 309L wire with the right shielding gas....and a bunch of practice....I should be able to get a decent weld right? I notice the stainless Magnaflow mufflers I have are mig welded stainless (probably machine rather than human) and the welds look great.

I'm pretty good at cutting and shaping.....so if I should be able to put together a pretty good system downstream of the collectors to tie into the magnaflow x-pipe, then twin pipes out the back. What do you think? Get some practice in and see how it goes?
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Old 12th August 2017, 03:06 AM   #2
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Re: Stainless mig welding a custom exhaust system

No idea on the welding but are you going to try for a crossover system in there?

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Old 12th August 2017, 09:51 AM   #3
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Re: Stainless mig welding a custom exhaust system

Welding skill is down to a lot of practice, if you have the time, energy and some stainless scrap to practice on I'd say what have you go to lose to try it. A more capable welder (machine) is going to make it easier and if you can save a bunch of money on the fabrication, perhaps consider treating yourself to a TIG. Mine is the best $900 Craigslist investment I made.
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Old 15th August 2017, 02:28 AM   #4
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Re: Stainless mig welding a custom exhaust system

I usually won't try to tell people what to do but I will tell you this Cliff: GET A TIG!

I had very little experience with what I will call "precision welding" but managed to make my own stainless hard pipes for the cooling system and enjoy it. Stainless seems to hold its heat well and you can control what gets hot with controlling your arc. You seem like a fairly motivated and bright guy, I presume you will understand the benefits of the investment. Let me just say that once you try it and figure it out, you'll love it.

Read up on stainless too. You'll want to purge it on the inside in addition to the gas going to the torch.

If you're feeling particularly saucy, get an AC/DC TIG and also put welding aluminum in your bag of tricks. Stainless is way easier...

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Old 15th August 2017, 04:42 AM   #5
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Re: Stainless mig welding a custom exhaust system

I presume one would need to wire in a 220 high amp power source into your garage to power said welders? In my youth I did a lot of DC stick welding. Could lay a pretty nice bead with a 7020 stick. Fabrication is something I've outsourced in the last few years but am getting the itch to take it back on. If you want it done right or at least your version of right then you need to do it yourself so they say. I think I agree.
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Old 15th August 2017, 07:29 AM   #6
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Re: Stainless mig welding a custom exhaust system

We do it every day at work. With MIG you should use 98/2 Argon-CO2 for shield gas and purge the internals with same. What alloy is your tube? 304L?


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Old 15th August 2017, 07:29 AM   #7
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Re: Stainless mig welding a custom exhaust system

Thanks fellas, appreciate the words of wisdom and advice here. Good ideas all.

I'll do a little practice with the stainless mig on some scrap (will check out the backside purging too). In parallel I'll look into tig. I know I like the looks of tig stainless welds.

Kelly: yes, using 304.

I'll post a few pics as I make some progress here.
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Old 15th August 2017, 04:09 PM   #8
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Re: Stainless mig welding a custom exhaust system

You can mix up some solar B flux with rubbing alcohol and put on the back side of your welds and it works like purge gas it is good for things you would have to build a box around to fill with purge gas. But for tubing it is easy to purge
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Old 15th August 2017, 04:11 PM   #9
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Re: Stainless mig welding a custom exhaust system

Mike you also don't need 220v I have a miller dynasty 200 and it can run on 120v all the way to 575 3 phase just plug it in and it adjusts automatically. But for aluminum you will want 220v to be able to through enough amps at it
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Old 17th August 2017, 06:35 PM   #10
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Re: Stainless mig welding a custom exhaust system

You will need to back purge. We use a second tank and regulator, but you can rig something to work off a single regulator. We have tried without, and while the outside looks fine, the inside was always horrible.... And grinding SS inside a pipe is a real PITA. Painter's tape on both ends of the pipe works, so don't think you need something elaborate.

IMHO, Stainless is easier to weld than most steels, if only because it tends to be cleaner and more consistent. A little practice and you will be good to go.

Dito on the Miller Dynasty. Tig/Arc, 110v-480v all in one machine. DX models give you all the control you need to weld AL as well. Though I wish I had sprung for the 400 (which will not run on 120). But they are EXPENSIVE for a home shop.
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Old 17th August 2017, 10:51 PM   #11
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Re: Stainless mig welding a custom exhaust system

Also what ever you decide get your filler Rod or wire with si in it. It is silicon and it wets in and lays flatter. And get one grade higher than the base metal. I.e. 304 base get 308- 309. Or 316.
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Old 19th August 2017, 07:37 AM   #12
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Re: Stainless mig welding a custom exhaust system

Quote:
Originally Posted by Frank833 View Post
IMHO, Stainless is easier to weld than most steels, if only because it tends to be cleaner and more consistent. A little practice and you will be good to go.

Agreed......and because it doesn't conduct heat very well it's easier to control the puddle and typically less heat induced stress and distortion. Copper and aluminum alloys are at the opposite end of the scale.


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