This is what I use everyday at work. They are about $400.00 so too much for a home hobbiest but if you find yourself doing a lot of projects with spot welds, I HIGHLY recommend it. It has a few different "clamps" that go behind the weld with up to about six inchs of depth.
Basically using this tool or not you have to look at drilling out spot welds as
"unbolting" the part. If you were unbolting the part would you start prying on it with a chisel BEFORE the bolt was out? No, so don't do it with a spot weld either. Take your time and drill STRAIGHT into the spotweld completly removing it. If the weld is bigger than the drill than make two (that is all it usually takes) offset cuts. Place it so it cuts about half the weld then move the drill over so you can cut the other half and not have the centerpoint "in" the first cut. This will usually prevent the drill from walking. If you try right in the middle and then try cutting a little weld left you will likely have the bit walking and screw up your bit and the hole.
Drill it out without hitting the bottom panel too much. But really you can strategically drill right thru both panels and then use that hole to plug weld your new panel on. So SOMETIMES it is not nessisary to use a spot weld driller at all. Though I always do because I have the need tool that does all the work
After you have drilled out the weld, I have found the
BEST tool for spliting the panels is a gasket scraper! You know the real nice ones (I have been using a Snap On one for about 15 years) what looks like a screw driver but has a "blade" at the end about one inch wide. They are thin and slip between the panels tapping it on the handle with a small hammer you slip the tool up to the spot weld (something will sometimes be left of the weld that you have to break) and tapping the hammer on the handle a bit more will run it right thru breaking the panel apart.
It is one of the very few times I will use a tool for something besides what it was intended.

It works like a charm.
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