This has been talked about in the past quite a bit, I'm sure a search will give you lots of good info.

My personal experience has been to do some of both. Lap welding will be easier for a newbie as your panels don't have to line up perfectly and you'll have less chance of burning holes. You'll need a flanging tool to do it properly. I picked up a cheap air flanger and it works great. Any lap welds I did were seam sealed both sides so no moisture can get in to start the rusting process again.

Butt welding requires careful preparation and trimming of panels to ensure a perfect "gap" to weld. Its lots more work ( and harder to weld) but when done properly ( with welds ground smooth) you shouldn't even be able to tell where the weld was made.

On the cab of my 66 I probably lap welded 75% and butt welded 25%. The factory lap welded ( with spot welds) lots of panels so GM must feel its ok.

Make sure you don't run long beads or you'll warp everything with the heat. Make small spot welds an inch or so apart and move around so things don't get too hot. Slowly fill in the gaps with more spot welds and keep moving around and letting things cool down. Once you start a nice bead you'll get the urge to keep going but don't! Take your time and do it right. Practise on some scraps first to get your welder set up before you start on your truck.

Last edited by dave64; 10/29/2008 2:05 AM.
Dave
66 GMC- father /son project with the "GMC KID"
36 Chevy PU- 4x4 lifetime project
64 Skylark- wife says its hers