Popper
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| posted on 7/8/02 at 01:01 AM |
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MIG weld or brazing chassis?
What are the benefits / disadvantages between MIG welding the chassis, and using brazing?
Seems to me that using brazing could be an alternative to less experienced welders and could be less expensive than purchasing a MIG welding
machine.
What are your thoughts?
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Alan B
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| posted on 7/8/02 at 01:38 AM |
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Hmm... I'd say MIG was the option for less experienced welders 
I know that for any welding you need good joint fit up but brazing is even more crucial. Also IMO the majority of joints aren't of the most ideal
design for brazing. Brazing likes good surface area contact and tight joints (for capilliary action) Let's not get confused with bronze welding which
although very similar is technically different.
I know that Lotus brazed (or was it bronze welding?  ) the seven (and maybe it still do) and brazing does have certain advantages, but I'd only
recommend it to an experienced brazer, again IMO.
Others may have different views
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merkurman
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| posted on 7/8/02 at 01:52 AM |
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I'd say mig too. lots of little joints that would waste alot of gas brazing. if you want to go cheap you could stick weld it with a cheapy buzz
box. but that would prob be too tough with gauge stock.
nick
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philgregson
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| posted on 7/8/02 at 05:33 AM |
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Mig without doubt!
Brazing probably has it's advantages including joints less liable to britleness and fatigue but mig is probably easier for many reasons:
I'm not vastly experienced at either and have never done a locost type of job with brazing but the first thing that imediately springs to mind is the
initial tacking issue. You possibly could partially braze joints initially but you could not easily maintain the integrity of the whole joint whilst
later fully brazing them.
Brazing would require the joints to be very tight and accurate and the radius on the corners of the tube would make this more dificult, leaving a gap
to fill on most joints.
Brazing would require heating of the whole joint at once which is a lot of localised heat compared with mig welding although the brazed joint would
suffer fewer problems from localised shrinkage than welding.
Good mig welding is definately a skill that takes time to aquire but certainly almost anyone can weld adequately with a little practice - there's
always the grinder if it goes too knobbly!
I would also guess that a mig welded chassis could probably be stiffer - although that is purely a guess.
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Simon
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| posted on 7/8/02 at 08:43 AM |
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Popper,
Don't even think about brazing. It will NOT be strong enough. It's just like soldering, but with a higher melting point (more silver than lead in
solder). You don't get a mixing of metals.
Get yourself a MIG / TIG / OA, and get on a course.
Alan B - I did hear of a kit car manufacturer some time ago that used bronze rod for welding - also my father runs an art foundry - casting works into
bronze, so I'm quite familiar with it. With bronze rod (which can be used for welding steel and bronze in any combination (very easily)) you do get
metal mixing. But not with brazing - as far as I'm aware anyway.
I'll have a read of some books tonight to see what I can find out about it!!
Popper - Hope this helps
ATB
Simon
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Simon
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| posted on 7/8/02 at 09:07 AM |
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Guys
Just found this link iro brazing -
http://www.geocities.com/CapeCanaveral/Lab/3495/Temp/basic.htm
Should be of some assistance
ATB
SImon
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merlin
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| posted on 7/8/02 at 08:09 PM |
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I know of someone local to me who is restoring a series 3 Lotus Seven and the chassis was completely braised. Looked very neat but is apparently a
pain to replace tubes etc. As posted above, the joints have to be perfect to start with, you can't bridge gaps like you can with a mig.
shit happens! (but why always to me!!)
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johnston
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| posted on 7/8/02 at 08:31 PM |
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i was told that brazing a patch wont pass mot anymore so if thats the case the i guess brazing your chassis wouldnt pass the sva
but then thats common sense and i know that our goverment agencies dont no wot that is
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Mark Allanson
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| posted on 7/8/02 at 09:21 PM |
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Brazing is definately NOT suitable for the type of steel section we are using, the strength (which can be STRONGER than a weld) relies on the
capilliary action of the moulten brass creeping between two overlapping pieces of steel. As the chassis is butted at every joint it would be weak as
hell. You also need to heat both sides of the joint to exactly the same temperature as the braze flows towards the hottest. The potential for
distortion is enormous. You can tack braze but as soon as you come to complete the joint, the amassed heat will ping the tack apart. Leave brazed
chassis to tubular spaceframes with preformed socketed joints (definately not suitable to one off's).
The only brazing on production cars that I know of is the upper A pillar to roof joint, and only because it produces a clean joint and is less prone
to corrosion in the highly abrasive high pressure zone created by the aerodynamics.
Basically, horses for courses, buy a MIG!
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semi42
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| posted on 8/8/02 at 09:22 PM |
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Mig Welding is the way. Just started tacking mine up and have got a dose of ray-burn...oops
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