Framebuilders - MIG Welding A Frame

Hey. First post in framebuilding. I'm going to be building a steel frame with the framebuilding club at my school (Cal Poly SLO). I've been MIG welding for about 10 years (I'm plenty good, and have welded plenty of thin material), and I'm wondering if I can MIG weld a regular diamond frame rather than TIG weld it. I have literally zero TIG welding experience and would rather not learn, though it is possible, if I want to put in the time (I have access to my school's TIG welders).

If it is ok to MIG the frames, how thick does the tubing have to be?

Any other tips are gladly welcome. Thanks in advance.

The short answer is no. There is not enough control of filler and heat with a MIG welder. Seeings how you have the TIG equipment handy, learn to use it, you won't regret it.

Here`s an ancient thread about MIG and bike frames. Some info might be outdated since it`s been a good three days since anybody posted to it.

http://www.bikeforums.net/showthread.php?628150-MIG-welding-and-Head-tubes

made me laugh

Yeah, sarcasm is usually fun, but I try to keep it at bay because I usually feel bad later- especially with no practical way of searching back posts any more.

Pista, I`d say that if MIG is what you have available, you may as well get some cheap materials and give it a shot. Hopefully you`ll glean something ot of that thread, even if it`s mostly links to other sites. I know it doesn`t specifically give the info you were asking about, but as you`ve undoubtedly noticed, there just isn`t a whole lot of MIGging going on in the steel bike world, so some imagination, experimenting, and guesswork will be needed.

Thanks for an actual answer with some information. What's the downside to MIGging frames? I've done plenty of thin wall welding. Does it create too much heat and distort the frame or something?

What's the downside to MIGging frames? I've done plenty of thin wall welding. Does it create too much heat and distort the frame or something?Against my better judgment, I'm gonna respond. Please bare-in-mind, that this repetitive "welding thinwall with MIG" Q&A is starting to grind on me a little - especially when those asking claim, "no problems welding thin wall", but turn right around and litter forums by asking if they can.

To be crystal clear, it isn't usually the MIG, in-and-of-itself that's the problem - it is the human under the hood that ultimately bares the responsibility of success. There is exceptions of course, but generally speaking, there's nothing wrong with using a quality MIG on bike frames... providing you can consistently prevail the elevated complexities of joining thin wall tubing + compound geometries + all position welding.... all at the same time. So in lieu of hammering a keyboard... why not go try it?

My first custom build frame was made by a guy named John Waite that MIG'd lots of frames together. This was in the early 90's and he typically used SLX which is .9 on the butted ends. As long as you don't go too thin on the tubes I'm sure you can build yourself a perfectly serviceable frame with MIG.

One problem you can't escape with MIG is cold starts. With MIG a lot of stuff is happening at the same time and is automated, which is why it is so fast. So the arc forms off the filler metal which immediately is advanced into the forming pool. If one is repairing sheet metal that is largely aesthetic aero in nature, then the fact that there is a tiny portion of the weld that is less that perfect is unlikely to be an issue. With high end structural work, like bikes and airframes, this isn't acceptable. With GAS welding or TIG, the torch heats the puddle to max penetration depth, and full liquid state before the filler is advanced into the puddle. So this problem with MIG does not exist.

The proper sequence with bike welding is likely to involve 4 tacks and 4 starts, that means 8 areas in the tube where the welding heat may not be perfect (and there is little likelihood that it is perfect as the process progresses either, since there is no independent control throughout). Overwelding the tacks is a whole other nightmare...

With MIG robotic welding of bikes, I can imagine that they might program the process to control the heat, and they could theoretically overcome the start-up heat, or minimize the starts and stops required. I don't know how they actually do it but process control is at least theoretically possible.

If you are flux shielding your MIG welds, not gas shielding them, then there are a series of other problems to deal with.

Obviously MIG is not suitable to custom bike making, but whether one can skate by on a home project for the fun of it is a different mater.

Distortion is a real problem with any process. But the real issue about asking this question in this forum is that nobody that posts here on a regular basis uses MIG on bike frames. So we're all just speculating. My way of thinking is that if there were any merit to using MIG on bike frames, people would be doing it. But I'll be the first to admit joining methods are subject to non-technical prejudices.

Against my better judgment, I'm gonna respond. Please bare-in-mind, that this repetitive "welding thinwall with MIG" Q&A is starting to grind on me a little - especially when those asking claim, "no problems welding thin wall", but turn right around and litter forums by asking if they can.

To be crystal clear, it isn't usually the MIG, in-and-of-itself that's the problem - it is the human under the hood that ultimately bares the responsibility of success. There is exceptions of course, but generally speaking, there's nothing wrong with using a quality MIG on bike frames... providing you can consistently prevail the elevated complexities of joining thin wall tubing + compound geometries + all position welding.... all at the same time. So in lieu of hammering a keyboard... why not go try it?

Thanks for the backhanded attempt at help.


My first custom build frame was made by a guy named John Waite that MIG'd lots of frames together. This was in the early 90's and he typically used SLX which is .9 on the butted ends. As long as you don't go too thin on the tubes I'm sure you can build yourself a perfectly serviceable frame with MIG.


One problem you can't escape with MIG is cold starts. With MIG a lot of stuff is happening at the same time and is automated, which is why it is so fast. So the arc forms off the filler metal which immediately is advanced into the forming pool. If one is repairing sheet metal that is largely aesthetic aero in nature, then the fact that there is a tiny portion of the weld that is less that perfect is unlikely to be an issue. With high end structural work, like bikes and airframes, this isn't acceptable. With GAS welding or TIG, the torch heats the puddle to max penetration depth, and full liquid state before the filler is advanced into the puddle. So this problem with MIG does not exist.

The proper sequence with bike welding is likely to involve 4 tacks and 4 starts, that means 8 areas in the tube where the welding heat may not be perfect (and there is little likelihood that it is perfect as the process progresses either, since there is no independent control throughout). Overwelding the tacks is a whole other nightmare...

With MIG robotic welding of bikes, I can imagine that they might program the process to control the heat, and they could theoretically overcome the start-up heat, or minimize the starts and stops required. I don't know how they actually do it but process control is at least theoretically possible.

If you are flux shielding your MIG welds, not gas shielding them, then there are a series of other problems to deal with.

Obviously MIG is not suitable to custom bike making, but whether one can skate by on a home project for the fun of it is a different mater.


Distortion is a real problem with any process. But the real issue about asking this question in this forum is that nobody that posts here on a regular basis uses MIG on bike frames. So we're all just speculating. My way of thinking is that if there were any merit to using MIG on bike frames, people would be doing it. But I'll be the first to admit joining methods are subject to non-technical prejudices.

Thanks for the information guys. I guess what I was going for when asking this question was personal experience, but no one seems to have ever actually done it themselves (as unterhausen pointed out), so I'm just getting a lot of speculation/guesses/opinion, which is totally cool, because that's all you can give someone when you haven't actually tried it yourself.

If you become an expert at it you can come back here and answer questions. I think many people here hate seeing unanswered questions, I know I do.

PistaRider311,

I'm genuinely sorry you feel my response was personal... it was NOT. Just to clear the air, take a moment and go back and look at your 'entrance' to the Frame Builders forum.

1. You are a student (or admittedly have access to) not only a variety of welding equipment, but more importantly, access to certified, IN-PERSON instructors.

2. You make it known that you have "10 years experience" welding thin wall. If this were genuinely true (maybe it is, but I don't know that) then .035" shouldn't pose much a problem for you, and therefor you needn't waste your time asking total strangers if you can. So what did the CC instructor say about bike tubes?.. or did you even bother to ask him?

3. You obviously posted prior to doing a search. Had you searched, you would've discovered at least 38 'MIG welding' threads (some more informative than others). But the most disturbing part was, in your apparent haste, you overlooked the most recent thread titled, "MIG welding and Head tubes" - a thread so recent, it was, and still is listed on the first page when you enter the Frame Builders forum. And had you read as far as post #7 in that specific thread, you would've instantly acquired the answer to your initial question.

And then you take offense when some of us get a little cranky.

FYI, I acquired my first AWS, GMAW FC 'cert' in pipe, and shortly after in SMAW on 7018LH (also in pipe) in the fall of 1980 - 'twas a bow-dunk, high school night class in Arlee, Montana (I was not a HS student) and went on to add 8 more AWS 'certs' to my measly list of credentials over the last 29-1/2 years...

But does that imply that I'm an all-knowing expert in MIGing thin wall tube?.... ... absolutely NOT! What it does mean, is that my 29 years under-the-hood blessed me with the wisdom to know when GMAW is suitable.. and when it's not. So in that light, you are correct, I likely don't have the GMAW wisdom you seek because just like the many other talented torches here on BF, I've taken the time to broaden my talents... and learn more efficient and cost effective ways to do it...

"Thanks for the information guys. I guess what I was going for when asking this question was personal experience, but no one seems to have ever actually done it themselves (as unterhausen pointed out), so I'm just getting a lot of speculation/guesses/opinion, which is totally cool, because that's all you can give someone when you haven't actually tried it yourself."

It's a little more than that in my case since I have spent at least 5 years trying to build quality bikes in the home shop environment with redneck methods. So I have tried everything from stick welding to.. OK except MIG. For two reasons as regards the latter, have basically had my fun doing it with stick, and I think in individual hands MIG is the least suited.

Also I would point out that while I enjoy speculating as much as the next person, the stuff about cold starts is plain fact, and is why MIG is allowed on certain jobs, and less so on high end structural stuff.

"But the real issue about asking this question in this forum is that nobody that posts here on a regular basis uses MIG on bike frames."

Another issue that bothers me even more is that while these newbie(s are welcome) questions always go into their pant size and what their girlfriend ate for breakfast details, they very rarely give one any real info on what the person is trying to do. They spend a lot of time describing them, and not the job. At least in this case he mentioned tubbing wall size. So OK, I'm sure you can weld with MIG a bike frame with 1/8" walls. In fact, it is pretty obvious from looking at factory stuff that crap welding works fine even with the 35-65 thou tubing welding. The problem is since we don't know the actual details it is hard to speculate and everyone is forced off onto tangents about what is good for the craft or what they did on the summer vacation.


Hey PAPA did they call it GMAW back in the 70s. I hate it when some kind of industry body changes all the letters and adds more without really adding anything to the general understanding. Congrats on the certs!