I'm seam welding my NB per the guidelines on the Flyin Miata site. Good quality TIG welds by a pro.
Is there any reason to consider continuous welds rather than stitch welding it? We are currently stitching it (approximately 2" weld, and 2" spaces)
I've heard from people with experience with other unibodies that stitch welding is less likely to expose other weak spots in the frame because it's not quite as stiff as continuous seam welds, so that would seem like the better choice for a car you plan to keep long-term.
In reply to GameboyRMH :
That's what I was thinking. Continuously welding seems like an opportunity for a weld to crack and run
It also seems to me that continuous may be a sign of someone who isn't doing great welds.
I've got overlapping stitch welds on the Targa Miata - effectively continuous. It's been worked pretty hard over the past decade plus and no signs of other failures yet.
It does seem unlikely to me that stitch welds are stiffer but not TOO stiff. How do you know exactly what that line is?
In reply to Keith Tanner :
What made you decide on continuous?
Was it basically "more is better"?
I agree about the "not too stiff" idea. That one doesn't make a lot of sense to me.
At some point the weak point is the limits of the metal, not the actual weld.
I've never done it on a Miata but I have performed FEA on other welded sheet metal structures comparing spot welded to stitch and full seam welds as part of a cost benefit analysis.
Generally speaking stitch is stronger than spot and seam is stronger than both but there are diminishing returns and deflection within the normal working range of the structure is very minimally improved when you go from stitch to seam. In the case of a car you're not expecting to stress the structure to the point of failure so the strength improvement isn't really important. If you stress the structure enough to tear a spot weld you've likely got significant other problems. Stitch welding however, can dramatically improve the rigidity within the working range. Seam welding will improve it further but only minimally.
In short, other than time and materials there's not really any downside to seam welding the whole thing as opposed to stich welding but there's also very little benefit. If you're doing it yourself go ahead and weld it all. If you're paying someone then just do the stitch weld.
The decision was made when the previous owner was welding it up :) I got the car as a bare freshly-welded shell after a rotary swap failed to happen. But his thinking was "more is better".
The metal is pretty strong in most areas that are being welded. I think there are four layers of steel in the door opening that are normally just spot welded together. For the V8 cars, we had a resistance welder and would just double/triple the number of spot welds in the door opening because that was high on the time/benefit ratio.
In reply to APEowner :
Perfect answer. Thank you sir.
I have nothing to add on the stitch vs continuous but TIG welding strikes me as an odd choice for seam welding sheet metal for a variety of reasons and if it were suggested by your "pro" welder I might consider finding a different "pro".
If I were to be doing this it would be with a MIG welder preferably with a finer gauge welding wire like .024-.030". MIG is faster, just as strong in this application and needs a lot less prep work. I would also argue that due to the odd welding positions you would need to get into to TIG weld the chassis your weld integrity will be more consistent with MIG.
Yes to MIG welding continuously.. it's what was recommended by other Jaguar XKE racers. Up on my Rotisserie I noticed some flex in the shell before and no flex afterwards. Since I reassembled it on the rotisserie putting that heavy V12 in place. I assumed if it was going to flex at anytime it would happen then. But even when I sat in it, no flex.
Remarkably the front 22 pound sub frame even with the heavy V12 it didn't flex at all.
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