So you cut out a spot weld and if you're really lucky or experience you a) hit it dead on a b) only nail the top surface. But I think most of us aren't quite that good and we end up cutting into the second panel. So, what do you do about that ... just ignore it or do you fill in the groove with weld and grind flush before installing the new panel ??

Mark your cutter so you know the depth not to exceed

Once you do a few, you will start to be able to tell when you get through the outer panel. You could try and spread the panel a little too so when you do go through the first one, it will pop apart.

I'm way beyond those suggestions now guys. 90% of them are done. So I need an answer to my original question. Leave 'em or fill 'em ?

I would try and use them (drilled holes) for the new weld spots from the new to the existing panel. Back it up with a piece of copper and make the plug weld. Grind down if you want it smooth.

At this point you can:

1) Fill the hole prior to panel replacement and weld it smooth.

2) Reuse the hole with the new panel and plug weld it with (if needed/possible) a backer.

I use method #2 as stated above often. Most of the time you don't really need a backer if you are proficient/fast enough to control the puddle when plugging the hole.

What, specifically are you removing on the car? What size and type of spot weld cutter are you using?

Do you have a set of cleco pins to realign everything? I suggest a set of 3/16 cleco's and an annular cutter (aka spotweld cutter) with a pilot bit for reinstalling the panel. This way you can drill you alignment holes 3/16 and hold everything in place with the cleco pins and as you remove them one at a time for welding use the 3/16 pilot bit to cut 5/16" or 3/8" holes in the top piece of metal that you are welding. This will promote good penetration and make life much easier, especially if this is your first rodeo.

Removed all spot welds with a 3/8 Blair cutter.

removed:
drivers side floor pan
both front inner fenders
complete rad support
upper cowl

still to go:
both rear full quarters

The plan is to cut off the lower portions of the rear quarters fore and aft of the axle than send the car out to be blasted before installing any of the new metal

I think it will still have enough structural integrity to go on a rotisserie given the remaining weight of the shell.

If, you're going to spot weld the new panel back, weld up the holes. If punching new holes to weld, use the drill through hole as a punch hole to weld. I pre drill for my spot cutter with an 3/32 bit so it won't skitter across the panel, then rock the cutter back and forth lightly till it goes through the top panel, every spot weld is different. Good luck

After you've done a few it's not too hard to only cut the first panel. You can sort of tell once you've gone that far.

Im a complete amateur at this but my biggest problem is keeping the thing centered and there's probably a better way of doing it but I always start with a drill bit in one drill to get a center hole started and then go after it with another drill that has the cutter in it.