Electrode for sand rail chassis?

Your life depends upon the weld.

You are welding a DOM 1-1/2" Diameter 0.095" wall roll bar and chassis.

Would you bronze braze or weld for dynamic loading and for crash worthyness?

What electrode would you choose for toughness and ductility?

BTW If you connnect all the tubes and pressurize the entire chassis, a pressure gauge will instantly show evidence of a crack.

BoyntonStu

Reply to
BoyntonStu
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7018.

John

Reply to
JohnM

7018 on .095" ?

My preference would be TIG.

Steve

Reply to
SteveB

I'm no expert on braze strength but personally I would not get into a vehicle that was brazed together, especially if done by an amateur (such as myself). It is said that a properly welded joint is stronger than the parent steel. I would not even consider brazing as an option.

Two things come to mind here. First, all joints would need a passage for air pressure. This would in many cases require drilling holes in the structure's members. Why take a chance on weakening these members with holes when there are other methods of inspecting weld integrity? Second, even if air pressure could flow through all parts of the chassis, how would a drop in air pressure indicate *where* the leak was? You would have to go over every joint with soapy water or something like that.

If I were to attempt to weld a tubular chassis together, I would first be sure of my welding skills and my knowledge of the pitfalls of tube welding (for example, when completing a weld around the circumference of a tube, the beginning of the weld has cooled and the steel at that point is thicker than the tube walls, so you'll need to backstep over the beginning of the weld to be sure that the two endpoints of the weld flow together completely and that penetration is complete in that area). Then I would get set up making test welds on scraps from the same batch of steel tube and destructively test them. Once I was sure that my welding equipment was properly set up for that steel I would move on to welding the chassis tubes.

Reply to
Artemia Salina

FYI Many race cars are brazed. All Fuli bicycles are brazed and most high end racing bikes are as well.

6013 = 60,000 PSI

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65,000 psi and 25% elongation. Not too shabby.

There are brazing alloys that are over 100,000 PSI.

IMHO, an amateur can 'see' a good braze easier than he could 'see' a good weld. If it flows, it holds.

The flexible nature of a braze is a very nice attribute.

I have a recumbent trike that I built that has one main tube brazed to the head tube. No problema.

BoyntonStu

Reply to
BoyntonStu

Well, then, just do it and go racing!

Steve

Reply to
SteveB

Bicycles I knew were brazed. Car frames? That's news to me. Seems to me that a car chassis would be subjected to much much more stress than a bicycle frame.

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Do those numbers represent the bond strength of the joint, or is that the strength of the braze material itself?

Reply to
Artemia Salina

I did a little Googling:

I can't speak for "modern" tube frame race cars, but standard practice for road racing cars with tube frames in the 1960's and 1970's (such as

formula fords, sports racers, etc.) was thin wall mild steel tubing, in the range of 3/4"-1 1/4" diameter by .047 - .062" wall, joined by a process called "nickel-bronze welding". The latter is a high nickel content brazing rod, applied with an oxyacetyline torch, with minimum heat so a bead is created, rather than a full flow typical of ordinary brazing. I believe that it is stronger than simple brazing. The common alternative of the era was TIG-welded high alloy "chrome- moly" steel, I think typically 4130. This latter construction called for normalizing the entire frame after assembly, which wasn't feasible in most small race shops. British suppliers, and US suppliers of cars sold to markets typically dominated by British suppliers (i.e. the purpose-built road-racing car market) tneded to use the nickel-bronze welding. I believe that sprint cars and the like were more likely to use alloy frames. I don't know why TIG (or MIG) welded mild steel frames were not more common. At least in the nickel-bronze on mild steel construction, there were no

lugs of any kind. The tubing (typically round, but sometimes square or rectangular) was carefully fitted to to minimize any gap at the joint prior to the brazing. One of the benefits of the nickel-bronze approach may have been that the bead provided a larger surface area, and acted a bit like a small lug.

And :

At least half of the British motorcycles ever made had their frames brazed together - Norton, Triumph, BSA, and Royal Enfield all did it - back fifty years ago the US Crosley car company built engine blocks by brazing together pieces - brazing is also used to hold together some modern tube-frame racing cars.

And:

have to second this - brazing, if done properly, can actually EXCEED the strength of standard welds. There have been reports where brazed joints have been pull-tested in the 80K PSI range, and most standard arc joints are in the

70K PSI range.

BoyntonStu

Reply to
BoyntonStu

Artemia, Brazing is a FAA approved standard for aircraft. It's also fine on spindles and cages on drag cars. (NHRA/IHRA) certified classes AA/FC TA/FC TA/D ect.and below. A brazed weld can indeed be superior and we use our blowdown tubes from the valve covers to vent into the frame as a "catch-can" under vacuum. Bourgett motorcycles also use the inside of the frame in lieu of an oil tank to open up space and provide a bigger heatsink surface. The engine oil is circulated and cooled and fed back into the engine using the frame itself as the tank and cooler. Pretty slick. And Spitzer, TRZ, and most other good drag frames of the older days were sticked with 6013 and on the certification sticker and paperwork for annual inspections. My 235" 2004 Spitzer TA/D is all TIG and MIG now. But if your gonna run stick. Check with any sanctioning body before you get started if you are in a competitive event. You might be surprised to find a fly in the ointment. I have gas brazed onto many frames in drag racing. I did so under the guise of the fact if the FAA approves it, it's gonna have merited science behind it. Sealing a frame can be a real bad idea. corrosion can be a factor and at the lowest point I always have a small hole for air with a small pipe-plug to drain off blow by that crept past the blowdown tubes. As far as anything like the rear carrier or link mounts I put a lot of heat and filler down. I have cracked a few frames and this season, bent one into a horse-shoe after a knarly crash. A lot of the areas that were welded had shown no signs of fracture with Magnaflux (A post-mortem on the effects of 195mph to zero in a few hundred feet sideways in my last Alcohol dragster before I got the new car I can't drive from results of the crash) I can photograph some of the welds and send them to you. I have been putting well over 2500hp to mine and there is attrition and rework still, regardless if it was welded by god himself.

Have fun going fast, and let me know if you need a powerplant, parts, or tranny's I'm between shops and working out of a friends auto shop and he is pissed my trailers and two of his service bays have my cars in them as well as my clients work! I have spare engines all over I'll never move. I'm going to break them up for parts. KB Hemi's, Donovan 640CID's and a hodge-podge of blowers, good blocks,heads, cranks, rods, slugs, sleeves, injectors,magneto's, Lenco's, PG's, Insane cams I had cut myself, etc. I also have a bunch of Wilwood and Strange brake components and spindles if you need em for a frame-up build I'd rather a guy here or racer get them than an idiot on E-bay!

All the best, Rob Fraser

Fraser Competition Engines Chicago, IL. Long Beach, CA, ( Soon!)

"Artemia Salina" wrote in message news: snipped-for-privacy@sheayright.com...

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Reply to
RDF

Oops. I meant this to be addressed to Stu. Sorry about that... But the parts are still to anyone interested!

Rob

Fraser Competition Engines Chicago, IL. Long Beach, CA, ( Soon!)

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Reply to
RDF

Not commonly these days, but go back to the '60s and look up "Superleggera" (spuerlight) construction of aluminium panels over brazed tube spaceframes. It's good enough for Aston Martin and the famous Maserati "birdcage".

Reply to
Andy Dingley

For maximum ductility on thin wall tube, 6013.

Reply to
Ernie Leimkuhler

Stu,

I'm not sure if you're posing this as a hypothetical or real life scenario.

If the latter, your question will likely be answered by the rules of the racing regulatory entity.

Mind you I'm ranting purely as an amateur welder, althouth a fairly well read one.

But there seems to be a large measure of harmony between the generally accepted practices of the race car and aircraft industries.

I think I'm on solid ground to assert that, among the homebuilt aircraft and racecar building crowds, both gas welding and TIG are the standards to which the other processes are merely compared.

Not that I'm qualified to do either, but my natural choice would be to gas weld 'em with an aircraft type torch.

Vern> Your life depends upon the weld.

Reply to
Vernon

Wow! That's amazing! I never would've thought that brazed joints could be stronger than welded ones!

Still don't know if I'd trust it though! :-)

Thanks for the response.

Reply to
Artemia Salina

Artemia,

That is why a forum is so educational. I would gladly trade my many held misconceptions for accurate information. The process is called 'Science'.

I have ridden many miles on a single brazed joint. At first, I was very hesitant to trust it, because like you, I did not have any first hand experience.

The nice thing about brazing is that you can always come back to a joint to add a little more here and there and it all flows nicely together.

Another advantage is that all you need is a pair of sunglasses not a welding helmet. (I don't even use them)

I have been learning to stick weld and I find it to be very pleasureable when it makes a nice bead. It feels good to see steel melt and puddle.

I thank Bob Fraser for his most valuable input. It is nice to know that what I plan to use at 70 MPH actually worked at 250 MPH!

This is my project:

A 2F1R hybrid 2 seater. (That means 2 wheels up front and 1 wheel in the rear)

Not quite a Trihawk. Aero. A 2 seater with about 10 cu ft of cargo space. Not a short micro car. (Dymaxion influence)

500-600 pounds of batteries up front. 65/35 weight ratio No power steering. Disk brakes. The swing arm pivot axis located jackshaft to mount the drive sprockets. Regen and disk braking in rear. Weight under 1,500lb (hoping for 1,200) Roll cage protection using DOM 1-1/2" Dia .095 tubing. (6013 or brazed) Is this sized/process tubing overkill? Roll cage/frame designed to allow batteries and engine to go underneath in a head on collission. Fabric or other lightweight body panels. Rechargeable A/C unit (make ice at night, make ice when at work when recharging batteries) Engine/tranny is from a 1981 Kawasaki 550 GPZ. Engine on right side with chain to jackshaft going forward. 10-20 HP ADC motor on left side. The goal is 45 mph for 30 miles commute/shopping in town. 70 mph top speed. 50+ mpg on engine.

BoyntonStu

Reply to
BoyntonStu

Not to be pedantic, but super leggera is a method of car body construction - not car frame construction, indeed using very light tube structure covered by aluminium panels. Space frame chassis construction is something different. But indeed uses nickle or silver bronze welding of mild steel thin wall tubing extensively, and is still in use in current spaceframe race cars like Formula Fords. The joints are indeed stronger than the tube material in this construction method, as evidenced by my buddies Formula Ford crash this weekend where a few tubes got torn out - next to the joint, at the point of highest stress concentration but not in the joint.

This is not to say that Tig welding wouldn't be as good or better than nickle bronze welding - space frame cars made in the US normally were Tig welded, such as the Swift cars. But there are advantages and disadvantages to each method, understand them and know that either is a good choice if done well.

Brian

Reply to
Brian

most standard arc joints are

No they're not. 6013 has a required MINIMUM tensile strength of 60,000 psi but in actual as welded condition it will run up to around 78,000 psi. Same thing with 7018 (or any other rod), required minimum tensile strength of

70,000 psi while in as welded condition the true numbers will run from around 85,000 psi to around 93,000 psi. If that's not enough it's a simple matter to go down to the local welding supply and buy 11018 and thatwill put you into the 120,000 to 128,000 psi range using a commonly available, easily run consumable. Just regular old run of the mill stick rod.

JTMcC.

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Reply to
JTMcC

Please pardon the intrusion, but I gotta ask....

When you guys speak of airplane and race car frames that are brazed, are they lugged joints ?? like on a bicycle frame ???

Please tell me it is not just a fishmouth like I would do for welding ????

Thanks

Jeff

Reply to
Jeff Sellers

Sorry, Jeff, the joints in question are close fitting fish-mouth joints - also butt joints where two tubes join. The vast majority of Formula One cars produced in Britain up to the beginning of the Monocoque era were made with butt jointed and fishmouthed mild steel tubes nickle bronze welded. The particular alloy used was a little unique in that it produced a fairly wide, thick fillet, perhaps 1/4" to 3/8" wide and up to 1/8" deep on a typical joint, and that had the effect of creating a low stress, ductile joint that was stronger than the parent material. In catastrophic failure these joints almost always held while the tubes themselves tore. A typical tube was 1" OD 18 Ga. mild steel. The chassis as well as the suspension members were fabricated this way/ Fusion Welding with Tig or gas was very rare.

Brian

Brian

Reply to
Brian

Nickle Bronze Welded sounds a bit different than a typical torch brazed joint. Is it in fact done with a torch in a similar way ??? Or what ???

thanks for the insight....ya gotta love this stuff !!

Jeff (Color me Curious) Sellers

Reply to
Jeff Sellers

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