The bolts are through the staybolt holes in the old sheet.
It took 2 1/2 hours however the sheet was preheated for a couple hours with a couple propane heaters so it was hot enough for the guys to cook hamburgers on for lunch just prior to the start of flanging.
Propane.
After the door hole is flanged we will weld the door hole ring to the sheet and then have it normalized. The backhead sheet will then be fit over the door ring. I prefer convex flanged corners in the firebox. The square corner on the outside is not an issue.
The video is not on you tube.
The job came out as good as we have done. Part of the secret was having more hammer men - particularly at the end when you are tired and swinging at a nasty and unnatural angle. Additionally, we have a really great bunch of young guys who do fine work.