Have a couple welding questions...

After drilling out the spot welds where the trunk floor attaches to the rear frame rails, what is the proper way to reattach a new floor so that the drilled out holes become hidden? Should new spot welds be created and the old holes filled or should new mig welds be created inside of the holes, or what?

Is it possible to spot weld from one side only? For example, when replacing the fuel tank supports on a 69, the rear flanges of the support are spot welded to the inside tail reinforcement panel. After drilling out the factory welds, can new supports be spot welded without removing the rear taillight panel? I have always been under the impressipon that spot welding requires an electrode on both sides but I might be wrong about this.

Spot welds in the body shop/restoration business are typically done with a Mig welder these days. The factory uses reststance spot welds, but many times it's not feasable to recreate these spot welds without sophisticated or funky shaped spot weld tongs.

How did you drill out the spot welds? with a drill bit or with a spot weld cutter?

You have to know which side your planning on doing your spot welding on to know which way to remove the spot welds.

If you simply remove the spot welds with a spot weld cutter, you can then drill your new spot weld holes where ever you need them or can access them, from either side. If you drill the whoile way through both panels, you may not be able to weld those holes shut again once the new panel is in place.

You really have to look over your project carefully and decide which way to approach your panel replacement.

Lets take your trunk floor for example. If I were to replace it, I would locate the spot welds in the trunk and use a spot weld cutter to remove them and leave the frame rails/gas tank supports intact. Remove the old trunk floor and make marks to know where the frame rails and gas support planges are, dill a series of 5/16" or so diameter holes in the new replacement trunk floor, then re-fit the panel and start tack welding it in place. The welds around the perimeter would be a judgement call to know whether to drill all the way through or to remove the spot welds with a cutter.

I haven't actually done anything yet. I am just asking to make sure that I or whoever replaces my trunk floor does it properly.

So a spot weld cutter doesn't actually go all the way through? For example, if I started drilling from inside the trunk, I would drill just enough to break the weld but not far enough to go completely thought the frame rail or fuel tank supports, right?

Yes, a spot weld cuter will only cut through the top layer. You have to have a feel for when this happens and then stop drilling. The cutter actually makes a curcular cut around the outside of the spot weld "nugget". Many times, as your dilling and getting close to breaking through the top later, you'll see a little puff of smoke or dust. This is due to the fact that many times there is a bit of rust between the panels and when the cutter hits it, there's a small puff blown out...this is your clue that you've broken through the top layer.

Be warned though, that this isn't the case all the time. It's best to start/stop the drilling and check your progress as you go along to make sure you don't cut too deep.

I am amazed. Wow do I ever learn a lot every time I log in here!