Ask your WELDING questions here.

[dmaxmike]

Originally Posted by Strong Bad

Most (if not all) NASCAR chassis are MIG welded. A quality MIG weld is more than strong enough for roll cage work as well as suspension components. I've seen my share of crappy TIG welds in offroad racing. Multiple pass welds where the root pass is cold and fills gaps in poorly notched/fitted tube and then a "sic Bro weave" washed over the top. Total crap strength wise, but looks like a million bucks.

yes all NASCAR chassis are MIG welded. When you smash them at the rate they do you have to. But there is a lot of TIG work in those shops as well. But in the off road world and rally and everything else but roundly round racing its TIG welding for the most part because of its streith (when done properly) and the fact that most chassis are made of 4130 which is not a fan of MIG welding.



the "Sic Bro weave" made me LOL because i have seen my fair share of that as well. Everyone in so-cal with a flat billed hat and a tube bender is a fucking car builder bro!

[David R]

All processes can pass a bend or xray test when done properly. Matching the process with the job is a different thing.

Sent from the phone in my shoe. Maxwell Smart.

[walkingbear]

I was thinking of cutting a gas tank open. Repairing the pin holes and inserting a wedge shape piece of metal to the tank to increase the capacity
Good welder Miller 211 mit. Noob welder who has a ironworker friend who will help me

Can this be done?

[Strong Bad]

Originally Posted by dmaxmike

yes all NASCAR chassis are MIG welded. When you smash them at the rate they do you have to.

This is exactly my point, MIG welding is more than strong enough on cages that can take the bashing NASCRAP doles out. The quality of the workmanship is more important than if it is TIG or MIG.

[Strong Bad]

Originally Posted by walkingbear

I was thinking of cutting a gas tank open. Repairing the pin holes and inserting a wedge shape piece of metal to the tank to increase the capacity
Good welder Miller 211 mit. Noob welder who has a ironworker friend who will help me

Can this be done?

Of course it can be done, the question is do you or your friend have the skills to do it right and not make a fugly mess?

[David R]

I refuse to weld gas tanks any more. Its not worth the risk to me.
Do as you wish. Have the tank steam cleaned out by a radiator shop before cutting it open. Purge the tank with Co2 or welding gas.

Look closely at the pin holes. The area is usually bigger than you think. This can be repaired with a good two part epoxy like 3M Structural adhesive available from Napa and other places.

Can you put .023 wire in the Miller 211? Do you have C/25? Can you weld thin sheet?

Good luck, Take pictures

David

[David R]

Bolt was sticking out of the head. I weled a nut to it but the bolt broke off again in the head



SO I welded a tit to it.



and a nut to the tit




I did a bunch.



Miller Passport .030 wire. 280 ipm about 130 amps

[Benesesso]

Originally Posted by dmaxmike;20174959[SIZE=3

But in the off road world and rally and everything else but roundly round racing its TIG welding for the most part because of its streith (when done properly) and the fact that most chassis are made of 4130 which is not a fan of MIG welding. [/SIZE]

Right on. 4130 is best gas welded, but TIG also works well. If anyone wants to know why, just ask.

[Benesesso]

Originally Posted by LexLeroy

Here's the daughter's bike so far - brass fillet brazing for some of the lugs and then silver brazing the lugs to the tubes. The thing behind the bike is the frame fixture that I built to hold all of the pieces together for pinning and brazing.

And here's two of the home-made fillet brazed lugs, shown with a production investment cast lug, prior to being silver brazed into the bike.



Brazing with oxy-fuel is fun but I'm pretty stoked about learning TIG... looking forward to lots more conversations in this thread.

Beautiful looking, but there could be a problem with them. Brazed joints work very well when stressed/loaded in shear (lap joints), but not so well in tension. Tension is where welding shines. Your lugs appear to me to relying on the tensile properties of brazing, and they may fail.

Well made brazed joints have lots of overlap/shear area, as do well made adhesively bonded joints.

[clintnz]

Just about to deploy the new TIG on some 4130 tube for the 1st time. Making a simple soft pannier rack for a friend's XT250 out of 5/8 dia .065 wall tube. The design should be plenty strong even if my welds aren't 100% but it's always nice to do stuff right. I will practice a bunch before starting on the job. I've built a couple of similar racks that have worked well but have had a mate do the actual tube welding as we didn't have the gear then.

The key joints will be where the tube is butted against the mild steel bushes I have machined up for mounting points. Will common garden ER70S-2 filler do the job ok? Post heat to cherry red with the torch for max awesomeness? Any other tips for the tube welding n00b?

Cheers
Clint

[mikejohn]

Originally Posted by Benesesso

Right on. 4130 is best gas welded, but TIG also works well. If anyone wants to know why, just ask.

Ok i'm asking

[NitroAcres]

Originally Posted by clintnz

The key joints will be where the tube is butted against the mild steel bushes I have machined up for mounting points. Will common garden ER70S-2 filler do the job ok? Post heat to cherry red with the torch for max awesomeness? Any other tips for the tube welding n00b?

Cheers
Clint

ER70S-2 will work just fine, Just take your time and do a nice job.
No need for all the post weld drama...just weld it up nice and you're done.

Opinions Vary...I don't know all the fancy text book stuff, but I have a few years of actual hands on TIG exp.

[LexLeroy]

Originally Posted by Benesesso

Beautiful looking, but there could be a problem with them. Brazed joints work very well when stressed/loaded in shear (lap joints), but not so well in tension. Tension is where welding shines. Your lugs appear to me to relying on the tensile properties of brazing, and they may fail.

Well made brazed joints have lots of overlap/shear area, as do well made adhesively bonded joints.

Good points. Here's the head tube lug jigged and heat-sinked prior to brazing - inserted rather than butted in order to get a better mechanical joint with some overlap. The brass flowed nicely into the joint - so much so that I needed to chuck the thing into the lathe afterward and clean up the ID with a boring bar.



And here's the head tube with the finished lugs silver brazed into place -



The homemade lugs join the sloping top tube to the (steering) head tube and the seat tube using silver brazing (56% cad free). The sloping top tube is mitered on both ends and butts against the head tube and seat tube inside the lugs. Since the top tube is under compression and the ends butt solidly against the head and seat tubes I'm thinkin' that I'm OK - the lugs aren't carrying much of any sort of load.

The bottom (lower sloping) tube is under tension, but that's silver brazed into an American-made investment cast lug at the head tube and into an American-made investment cast bottom bracket (where the pedals go).

But to your point, at least one builder that I know of who uses brass fillet brazing instead of lugs has experienced a failure of the junction between the head tube and the down tube on a bike that got used hard - a mountain bike. Fortunately I wasn't involved.

[Benesesso]

Originally Posted by Benesesso
Right on. 4130 is best gas welded, but TIG also works well. If anyone wants to know why, just ask.

Originally Posted by mikejohn

Ok i'm asking

When you buy 4130 steel, especially tubing, it is usually in the "annealed" condition. It is relatively soft and weak, but stronger than most common tubing made from plain carbon steels. Both of them will have a microstructure known as pearlite, as will the usual weld deposit from E70S2.

Pearlite is a very forgiving structure, meaning the steel can be bent quite a bit w/o cracking--usually. But if we take a piece of pearlitic steel and heat it above ~1350F, it transforms into something that is not pearlite--it's austenite. Aust. is completely different, but we can ignore that here, because what's important is what happens during cooling down to room temp.

Pearlite likes to reform at temps. between ~1100-1250F--dull red hot. It takes a bit of time to reform, depending on what steel is involved. It forms very fast in plain carbon steels (mild steel), in just a few seconds. But when we add elements such as Cr and Mo (what's in 4130), the time to change into pearlite can be much longer-can be ~10 sec. to a full minute or so.

The speed of transformation is what determines how a steel must be allowed to cool after welding. It's easy with mild steel-just let it air cool naturally. But with 4130 there can be a problem. If the weld area, meaning the area in the tube right next to the weld (the heat-affected zone, HAZ) cools too fast, it doesn't have time to change to pearlite. But as it cools down to ~500F, it will start to change into something called martensite.

Good ol' martensite, great stuff--but only after it's been reheated, preferably up around 1000-1100F for an hour or two (tempering). That's what structure your knives, wrenches and screwdrivers have, unless you bought the cheap stuff at HF. Untempered martensite is something you don't want, because while very hard it's also very brittle.

Back to welding. If 4130 is gas welded, a large area of the tubing gets red hot, so it slows the rate of cooling such that pearlite almost always forms. Same thing usually happens with TIG, although the area/volume of the red hot tubing is a lot smaller. But with MIG, the tube and HAZ are a lot smaller, so the rate of cooling is much faster.

Cold/cool steel can really suck the heat out of a weld area, and that can easily cause cracking in the HAZ. So why are so many MIG welds doing fine and not cracking? First, different heats of 4130 have different amounts of the elements that slow down the transformation to pearlite, and the allowable range of these elements is pretty broad. Therefore, for a given rate of cooling, one heat may easily crack while another won't.

Cr and Mo cost far more than steel, so steel makers "have a tendency" to use as little as possible, even tho the amounts added are tiny. But greed being so prevalent, some of them squeeze the penny harder than others. If unspecified, guess who gets the lean heats? Yup, whoever the steel salesman can dump them on--small ignorant shops, etc. Steels like 4130 can be ordered as "H" steels, meaning they must have more of the $$$ elements, but the average welder has no knowledge or info about that. They may cost a bit more, so watch out for the beancounter who's looking over your shoulder ("The damn spec. says 4130, and I'm not gonna pay extra for that "H" bullshit").

Then there's welder knowledge/lack of about the importance of cooling rates. A smart welder can use a gas torch and preheat the weld area which will slow the post-weld cooling rate. A welder working in the hot sun with real warm parts will have a lesser problem than some guy in Alaska in the winter, welding outside.

Then there's the matter of tube thickness. A real thin-wall tube can cool very fast compared with a thicker one. A welder who usually welds 1/4" thick stuff has probably never had 4130 crack and won't believe a word of the above.

Good luck and keep rubbing your rabbit foot.

Here's a little test result that I demanded after I paid a surprise visit to a fabricator in Italy and caught them welding a steel with a lot more Cr and Mo etc. than 4130 w/o preheat. Preheating was mandatory for the MIG welds, especially for the tack welds holding the thing together during fab. The "thing" was a carrying goodie for a 550 ton nuclear steam generator.

Rather than starting over, we, in Milano, had a huge oven big enough to heat the whole damn thing to a good tempering temp. I agreed that bend testing would prove the the welds after tempering (post weld heat treatment, PWHT).

Here we go:



I'm sitting there after my boss asked me how sure I was that the carrier wouldn't drop our $$$$$$$$$$$$$$$$ steam generator. I said "pretty damn sure", and he said, "We'll see--sit here". He couldn't do that stuff in the US with OSHA rules, but in Italy----.

[dmaxmike]

That is quite a good explanation of the art of 4130 welding! That whole undercarriage was built out of 4130H?