Grinding Welds down when building a custom stainless exhaust?

My buddy just picked up some stainless MIG wire to finish up this exhaust we have been working on. We don't have access to a TIG and im a bit reluctant to see how this comes out. I am going to rent a 3 mix shielding gas tank for a few days to do the job.

i know some experienced exhaust builders can Tig pipes together and grind flush smooth with little to no integrity lost etc. this is done on lots of show car hot rods and customs.

can this be done as well if we MIG the pipes really good or is this a bad idea overall?

we are working with 304 Stainless and we planned to scotchbrite all the pipes when done for a nice brushed look.

 

The real nice ones have hours in the fitting and fuze the tubes together without any grinding.

 

Vee the joint your welding then there should be enough penetration to hold the pipes together if you grind the welds flush.

 

guys do you know if i can use my 75/25 shield gas or i really need tri mix to do this job?

 

i'm nobody special...pretty decent mig welder....i have a tig,but am just starting to learn how to use it....bought some 304 stainless at a swap meet and decided to try to mig weld it with stainless wire...used the same combo gas...argon/co2....it actually came out great....ground it and polished it....give it a try on a s**** piece....you might be surprised

 

Used to weld a lot of stainless with tig and mig. All you need is Argon/CO2, 100% penetrtation is going to be pretty easy on an exhaust pipe. A little advice buy a can of spatter spray and use it religiously.


When you are grinding a sand paper disk is better then a stone, 80-100 grit to start and 300-400 grit to finish. Do not stay too long in one place once you get it hot it will not grind at all.

Practice first on s**** to get your technique and setting down and make sure that you fit the pieces really well. Even 16 gauge can be welded without V notching.

 

What porkn****** said with the spatter.
I'd consider wet rags right close to the seam possibly.

There are SS grinding discs,
they don't glaze like the others,
but they do knock alot off quickly.
Than finish it up with the roloc or sanding pad at 60/80,
than finer for the finish.

You'll figure it all out by the time you finish!
Once you get a TIG,
you're going to wonder why you ever did it with the mig.

TP

 

if you use a argon gas perigee inside the pipe ,the weld will look like the same inside and outside for a full pen , you can clean the weld with a gratex wheel for a smooth finish

 

Fit up is going to be the key, especially if you'll be **** welding and polishing mig welds. Hopefully you have 16gauge so you can get some of the imperfections out.

With a tig, you can take advantage of the expansion movement of stainless by throwing some heat on the pipe that needs to come out at the joint then fuse it once it walks into position.

Stainless also stick welds very nicely.

 

Use of a gas backer is good, they also have backer rings. Stainless should be quenched to keep the stainless properties in the weld and heat effected zone,

 

While ****** is right that you can use C25, you will be much happier swapping to a tri-mix or H95 (95% Helium) gas. It will produce a much smoother and cleaner weld. There is too much oxygen (CO2) in C25 and it reacts with the alloying elements in stainless and thus creates alot of splatter and welds that have more voids and are susceptible to inclusions.

 

When grinding and sanding do not use discs that have been used on iron or steel, the iron or steel picked up in the disc will deposit onto the stainless and can rust.

 

"V" cut exhaust tubing????

 

I built a dairy research barn years ago and the crew installing the equipment Mig'd all the stainless. It was a new setup for them and they were impressed.

 

If all that can be managed is noodle welds you might want to V it first.

 

Your not doing food grade or running liquid through the pipes so don't waste money on trimix. Also no need for backing rings or argon purging, it's exhaust pipe and fitting and tacking then weld on the bench and post some pics.

 

Probably used STT (or surface tension transfer). For the OP, think polishing, not grinding. Every scratch you put into the tube has to be polished out, and if you're not gentle you'll polish right through it. The gas inside the tube method is called purge welding. Usually used for sanitary purposes but if you purge an exhaust, in theory you could polish the outside smooth and you'll still have your weld reinforcement, but just on the inside of the tube. Probably not really an issue for a well supported exhaust though.

 

I like the look of the Raw welds. But those are T. I. G

 

No, this was a small mig like most of us have at home 140or170 setup. I pulled a couple beads and was impressed back then. This was 20 years back and I was busy welding cow stalls with stick. My first welding job!