advice needed for body work

[JerryC]

I have a 1963 GM4106,  Some of the very rear (around the rear window) and very top front is steel the rest of the skin is aluminum.  The original rear window was already cracked and 4-6" of spray foam insulation was already on the inside over the window and most of the rear area so I kept it that way for many years.  With the crack and old seal the entire area eventually rusted and, I knew this was coming, but have already started redesigning and rebuilding the back end around this window.  I am using 11 gauge 1-1/2" square tubing for structure, 18ga cold rolled steel for a skin, installing a 24x18 double pane non-opening window 'cause we like to be able to look out the rear.  Some specific questions.  There are some areas that will have to be riveted to match up with the original design and where AL and Steel will meet.  I'm using 1/4" ID SS monobolts for those areas and plan to use my wire feed welder for "spot" welds in areas where the steel skin is over the steel tubing by drilling small holes through the skin and "spot" welding it to the frame I've built.  QUESTION how big do I make the holes and how far apart do I space them?  One spot where two sheets of sheet metal will meet up (which my plan will have over a square tube) can I weld the ends together at the same time bonding them to the square tube structure (after welding grinding and polishing of course).  There will be other spots like on corners where I plan on doing the same....

Chicken and Egg question - Of course I want to prime and paint all this stuff but can't paint anywhere I'm going to weld if I use this spot welding technique - how do I get or do I need to get primer & paint between the skin and the square tube structure? Will just painting from the inside give me the needed protection?  In areas that will be riveted I will be using "Manus Bond 75-AM" between layers of AL, Steel, and or the structure and plan on at least priming the AL before I bond and rivet.

I consider myself fairly good metal working skills but lack a whole lot of experience so any advice will help though at this point (now that I finally got access to a bus nut board) may be somewhat academic at this point since I am well into this project (about to put skin on) - Jerry

[Highway Yacht]

Jerry.. I've read that you can drill 1/4" holes every 4 inches and weld those skins to your square tubing and then ground down the welds flush to give that smooth appearence. I've also heard the biggest problem in doing that is that sometimes the heat from the wire welder or the grinder can distort the thin skins.

Jimmy

[robertglines1]

3/16 /or 1/4 would work fine. Do you have a spot weld mode?      Steel to alum must have mechanical separation/ tape or sealant of some type to prevent deterioration  think you are on top of it. Measure your rivet pattern and and match the spacing there 3 or 4 inch .  Bob

[hanks69chevy]

they also make a primer paint that's weldable.

[JerryC]

Today I've begun putting on the skins - the curved areas are going SLOWLY - or how I spent my WHOLE summer! 

SPECIFIC QUESTION - on the corners where a vertical sheet metal will meet a horizontal one (making a ninety degree turn around a square tube)  HOW does one finish off these corners - just cut the sheet metal, weld along the edges, and grind smooth OR would there be any reason to hammer the roof sheet metal around the edge of the vertical sheet metal and what I can't grind smooth use body putty to make smooth - kind of like a drywall edge. 

PS although academic at this point any thoughts on what thickness sheet steel some of you use?  I'm using 18 gauge cold rolled steel.  The original steel in this area was significantly thicker but those were stamped steel body parts - I can't imagine bending stuff that thick around the curves I've got to do.

[robertglines1]

Jerry I had better luck with 16 ga less waving. used 16 first then 18 then went back to 16 if you get the picture. The cold roll for some reason seems to hold paint better. Found that out on hot rods years ago. Don't know science just outcome. One of those things you don't have to know reason just results. Just my oddball way  Bob

[Barn Owl]

Document and take photos of your project. We would love to see it!

[JerryC]

I'm working on those pictures - just gotta take some or figure out how to turn them into a small enough file to attach - still new to this BB.  THANKS for the tip on a primer that is weldable - never knew there was something like that and got a can today at my local NAPA store.