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Poorly done welds, advise please

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  • ryanjones2150
    replied
    Tarry, the first set of pictures the OP put up the welds didn’t look near as good as the second chassis pictures.

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  • Bob Miller
    replied
    The first photo I looked at, photo Blogs upper right corner, the weld missed the tube and left a gap.
    The second frame looks way better.

    Good luck,
    Bob

    Photo number 3, not blogs.

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  • tarry99
    replied
    Originally posted by ryanjones2150 View Post
    That second chassis is certainly far superior to the first one you showed us. Doesn’t look cheap either.
    Not sure Ryan what other chassis were you referring too? Was it a 2x4 Off Road Rectangular chassis?

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  • ryanjones2150
    replied
    That second chassis is certainly far superior to the first one you showed us. Doesn’t look cheap either.

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  • tarry99
    replied
    Sorry I'm a little late to this discussion.....But on the subject of 4130 tubing and 309 ss rod it has been used successfully by many chassis builders and from the metallurgy reports I've seen with good reason as the key word I've seen is greater "Ductility " in the weld zone joint when other factors like back purging or normalizing is not commonly used ......I for one like it as you don't see the normal cracks you might see after using the chassis for extended periods.....in fact my race car was built using 309 pursuant to SFI specs....and not a crack in it after hundreds of runs.....But again I'm not saying anyone should use the product either as a sound , safe chassis must first start with a well engineered design , tight fitting clean joints , the right products and someone capable behind the torch and pedal. Click image for larger version

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  • Electric4Life
    replied
    4130 (chromoly) is welded with 70S2 filler most of the time...this wire is available for both MIG and TIG.
    MIG is a stronger joint but doesn't have the same repor as "TIG".
    If you need a definitive answer you need to find someone that inspects these types of chassis or even certifies them.
    Pictures on a welding forum aren't the answers your son needs when he's cartwheeling at speed.

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  • Bushytails
    replied
    When I think of a tube buggy, I think of something like this company's products: https://www.fabn801.com/products I think they have about a tenth the tubes! lol
    Click image for larger version

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    But, as I said, I come from the crawling world, not the racing world...

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  • rocky4by
    replied
    I believe it's designed like they are because of how many ways they take an impact while racing and in a crash. There not light any more, 5800 lbs maybe a bit more or less. There holding 70 to 100 gal of fuel now and getting about 2 mpg

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  • Bushytails
    replied
    Those look a lot nicer.

    I'm surprised how many tubes one of those has... Is it really any lighter than a ladder frame?

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  • rocky4by
    replied
    Thanks for all the great replies, lots of good help and information here. I passed on the first chassis I posted about, just many ? with it and being 1.75 tubing it would also be hard for me to get it Score tagged. Anything over 4000# has to be 2 inch now, so I believe we're going with this one now.

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  • ryanjones2150
    replied
    I went back and looked at that third picture, it’s hard to tell from the image, it’s a bit blurry. You can repair these things, like MMW said, just because it’s a race car chassis doesn’t make it magical.

    I’m not aware of anyone mig welding chromoly, but you are correct, it does not allow for sufficient heating of the welded material to resist cracking during cooling. You would want to preheat the material, not post heat. You could post heat, but unless you have the torch lit and waiting for you, it’s a bit late because it cools very quickly being so small in comparison. I am also not aware of any place that will heat treat an entire chassis after welding, which is why it’s important to weld it correctly and with the correct filler metal, which is not 4140 filler wire.

    Anything you buy in the racing world is a project unless you’re independently wealthy and can pay someone to do all your work. But I don’t think that’s what most people get into the racing hobbies for. If you get this chassis, or any other chassis, you will almost certainly need to make changes or modifications to it, so look at it like that.

    But I still stand behind my statement about the stainless welding, that will be a lot of grinding out and rewelding in what is probably the toughest joint on the entire chassis.

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  • MMW
    replied
    My opinion is yes you can reweld with tig. It is common practice to repair broken, bent, mangled race car chassis from accidents so why not this? Obviously it's going over a lot of the welds vs. a few but same principal. If something fails tech because of a few welds you fix them instead of scrapping the whole thing. Just my thoughts.

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  • Helios
    replied
    Are you allowed to MIG weld that kind of thing? I thought it was like a CrMo airframe, where it had to be welded with O/A or TIG to get enough heat into the welds so that they would "normalize" to some extent? Where are you getting cracking? On the MIG welds?

    Is it "legal"/"allowed" to MIG if you immediately heat-treat the welds right after welding? As Ryan said, I believe it's the "quenching" effect you get -- where the workpiece effectively "quenches" the weld material, cooling it off too fast and thereby making it brittle -- if you don't put enough heat into the whole thing, which is what often happens with MIG (I believe this is why MIG welds on car body panels often get harder than the hammers of he||, and resist dollying afterwards...)

    I have no idea, just regurgitating stuff I've read...from memory (which ain't great)...personally, I think I would "pass."
    Last edited by Helios; 09-13-2022, 07:36 PM.

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  • Bushytails
    replied
    The welds at the very top right of the third image concerned me the most... they look like zero-penetration booger welds to me. But, I'm not a great welder, so I may be wrong.

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  • ryanjones2150
    replied
    Man when I clicked on your post I was expecting to see some serious nonsense. Are those great welds? Probably not at the price you’re saying it is. But they honestly don’t look near as bad in the pictures as you describe in your text, but like mentioned, it’s hard for us to see in a few pictures.

    I can at least say this, I’ve seen way worse get through the tech inspection at the drag strip. The only guy around here that “professionally” builds custom chassis doesn’t weld them that good.

    That pipe cluster almost looks like it’s been welded with stainless, and that concerns me more than the appearance of the welds in your pictures. There are two reasons a guy would use stainless rod on that. First, he’s having trouble with porosity and instead of figuring out why and making it better, he’s leaning on the crutch of some stainless rod to get by. Second, stainless rod, especially 312, runs like butter and can make a hack weldor lay down some nice beads. Either way, it’s concerning. If those are full penetration welds using stainless, you run the risk of them cracking unless the backside of those welds were shielded. If they were, they’ll probably be fine. If they were not shielded, the backs are probably all sugared and nasty and they will crack.

    These are not at all abnormal concerns when you’re buying a used custom chassis, but there was nothing in your pictures that would make me barf. By the looks of the construction, the fit ups look good. The angles look good. The coping looks good. If I saw poor fitups, I’d certainly have cause for alarm.

    This is just my opinion based on a few photos though. I’d say trust your eyes and look at the overall construction to determine whether is been built by a hack or someone that took some pride in their work.

    But to answer the question on whether you could just wash those welds in nicer with the tig. Yes. Generally speaking, with 4140 and 4130, unless the guy used 4140 rod, the heat treating wasn’t made brittle. The weld area is small enough that just welding a bit slower and letting it heat up good is plenty to keep it from crash cooling, which is the problem with chromoly you want to avoid. It’s not the heating up, it’s the cooling down.

    Hope that helped.

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