Morrisman
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- 7,188
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- Staffordshire, England
yeah thats because the metal shrinks as it cools, if you want to increas the gap between the two panels and have access to the back for a dolly you can hammer onto the tack. if its starting to "V" while being tacked, its best to try and staighten the two sections then.
To be very pedantic, it doesn’t actually shrink per se, it expands and compresses metal around it, and when the expanded bit shrinks back to normal size it effectively pulls the other bits in with it.
If you can clamp it to stop that happening it goes nowhere.