Observations from tack welding a roof cut in....
- Roof tack 1.jpg (65.7 KiB) Viewed 267 times
Firstly thanks to Brett (Wilma and Project 2) who came over to discuss welding strategies and give me some reassurance. We concluded that there could be a number of ways to approach tacking the roof cut in but that getting the front join right was most important so probably start in the middle there. The front join was pretty close, not even 1mm and maybe touching in a few places - in hindsight too tight.
I felt that the rear corners were a good fit and my reference so I clamped up the rear:
- Roof tack rear view.jpg (49.8 KiB) Viewed 267 times
- Roof Tack RH rear cnr.jpg (74.86 KiB) Viewed 267 times
Feeling that I wanted to make sure the rear corners stayed put I decided to do tack #1 about 7 inches forward of the RH rear corner - I was just a convenient spot. I figured that the rear wouldn't move as it was clamped and had the flange in it which was right. I didn't think tack #1 would affect the front join but that if it did there was plenty of metal to play with to rectify it - or I was prepared to cut the tack and do something different.
Tack #1 was enough to close the front join and make a slight overlap both to the left and right of the centre of the front join. Tack #2 on the LH side forward of the rear corner only alleviated this slightly. Tacks 3, 4 and 5 fixed the overlap on the RH side of front join but I had to very carefully use a dremel and cutting disc to relieve the overlap on the LH side. I then worked on the LH side working tacking alternatively down the front join and forward from the rear tack to creep up on the front corner.
- Roof Tack LH side.jpg (50.13 KiB) Viewed 267 times
- Roof Tack LH Front Cnr.jpg (39.58 KiB) Viewed 267 times
That all went nicely but interestingly created an overlap on the RH front joint below tack #3 - go figure... Then contrary to what I thought would happen, tack #17, the next one forward from Tack #1 on the RH edge, fixed it...But it also succeeded in significantly closing the RH edge gap as did successive tacks along there.
- Roof Tack 2.jpg (51.23 KiB) Viewed 267 times
Luckily the roof patch was always sitting inboard enough for me to carefully grind the mating edge back to make it fit. As per the LH side I crept up on the front RH corner alternating tacks on the edge and front. Blew a few holes and moving the roof patch panel into place became increasingly harder. Needed a prybar to help get the final few done.
Anyway, 33 tacks later averaging about 6 tacks an hour (there was also lots of looking and head scratching going on) it looks like it fits pretty well. The profile looks good. There are a few spots along the front join that will come up with more tacks and I haven't started on the rear, but so far so good. Still not sure that I've worked out how metal moves in response to welding though...