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Old 01-28-2014, 10:22 PM
foamcar foamcar is offline
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Default Panel gap changes while welding

This has happened to me quite often. I have fitted a panel with nice even gaps and when I start tack welding the gap will tighten up at the other end. Suppose I could tack each end first, but am concerned that it will bunch up a little some where along that way if I do that.
fender patch fitted.jpg
I have attached pictures( I think) that show progress to date. After planishing the tacks, grinding them flush and replenishing the HAZ the gap opened slightly, but not all the way back. I used a Dremel thin cutoff disc to reopen the gap. Should I have tacked the bottom first?
Attached Images
File Type: jpg Ready to weld.jpg (79.5 KB, 70 views)
File Type: jpg First set of tack welds.jpg (74.3 KB, 81 views)
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Old 01-28-2014, 10:32 PM
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Kerry Pinkerton Kerry Pinkerton is offline
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Yep. That is the way it works. As you weld, the heat causes a shrink that pulls the panels together. Just planish the weld out until the gap is back where you want it and do the next tack.
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Old 01-28-2014, 11:38 PM
foamcar foamcar is offline
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Thanks Kerry

Gotta keep my eyes on that gap as I go so it does not get out of hand. Okay

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Old 01-31-2014, 05:38 AM
ozi jim's Avatar
ozi jim ozi jim is offline
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Hi Phil

Get some scrap and tack both ends first, then in the middle then in between them ect ect.
I do it that way all the time, I don't seem to get issues.


Jim
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Last edited by ozi jim; 01-31-2014 at 05:41 AM.
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Old 01-31-2014, 06:40 AM
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our college lecturer told us to set the gap at one end and slightly wider at the other, then as you tack along the length the tacks pull the gap straight
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Old 01-31-2014, 06:41 AM
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car looks good! 356?
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Old 01-31-2014, 07:05 AM
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You want gaps as absolutely tight as you can possibly manage. Every time you Mig weld a dot, it is going to shrink in a circumferential fashion, pulling from all sides. If you leave a gap, there is a better chance than not that the gap is going to pull together more as the welds shrink. On low crown panels such as quarters, door skins, hoods, etc, this means that as the shrink brings the gap together, it is removing some of the crown that supports that panel. Planishing out welds is enough work as it is without adding having to compensate for panel movement in the mix. This is a sure fire recipe for a nice big oil can in the middle of the panel. So, tight gaps will eliminate some of this work. You'll still see some shrink at the weld and HAZ, but it will be nothing like you'll see with panel movement.
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Old 01-31-2014, 10:21 PM
foamcar foamcar is offline
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Thanks for the variety of suggestions. As far as welding with no gap, my problem with that is I can't get good penetration. If I have a metal thickness gap I get nice penetration. Neil, yes a 356. I spent a little over 5 hours welding this panel in using the tack/planish/grind/palnish over and over method. Tedious process, but the results were pretty good for my skill level.

P1300561.jpg

P1300562.jpg

P1300564.jpg
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Last edited by foamcar; 01-31-2014 at 10:26 PM.
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Old 01-31-2014, 10:50 PM
Peter Tommasini Peter Tommasini is offline
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Quote:
Originally Posted by foamcar View Post
This has happened to me quite often. I have fitted a panel with nice even gaps and when I start tack welding the gap will tighten up at the other end. Suppose I could tack each end first, but am concerned that it will bunch up a little some where along that way if I do that.
Attachment 25988
I have attached pictures( I think) that show progress to date. After planishing the tacks, grinding them flush and replenishing the HAZ the gap opened slightly, but not all the way back. I used a Dremel thin cutoff disc to reopen the gap. Should I have tacked the bottom first?


Hi Phil there is a bit of info about taking and welding on my web ( under Video's)
Peter
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Old 01-31-2014, 11:30 PM
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[QUOTE=foamcar;89760]Thanks for the variety of suggestions. As far as welding with no gap, my problem with that is I can't get good penetration. If I have a metal thickness gap I get nice penetration. Neil, yes a 356. I spent a little over 5 hours welding this panel in using the tack/planish/grind/palnish over and over method. Tedious process, but the results were pretty good for my skill level.

Im just throwing it out there as a point of interest.
I use a tig and I have O/A ,with a mig in my mind because of the uncontrollable adding of material would it not make it harder to get penetration because its laying it on top.

Would a small gap not work better because of the material being introduced.
I use a no gap when I O/A steel panels because you are really fusing than welding.

I am not contradicting any of the previous comments I am truly interested.

How are your O/A skills as a point of interest Phil.
Only reason I ask is you can get some surprisingly good welds with OA once you get it sussed.
I have never miged a panel but would it not be a hard material to get the panel dressed?.
Jim
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Last edited by ozi jim; 01-31-2014 at 11:37 PM.
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