Gary,
There are a couple of different types of spot weld drill that I have seen
and the both have been mentioned. I have used both.
The first one looks kind of like an end mill bit. It has a fla end with two
cutting surfaces and a very small pointed tip that is intended to hold the
bit in the intended location while you cut thru the spot weld. Nice idea in
that it only removes the weld and if you stop when it gets thru the first
piece of metal you end up with a nice smooth surface on the second flange
behind the weld. These work gread until the point goes away which is usually
after about 20 welds as I remember. Once the point is gone you will have a
heck of a time keeping the bit in one spot. They are basically a throw-away
at that point.
The second one is the mini hole saw type. This has a small dia. drill bit in
the center which makes a pilot hole for the little hole saw. These last much
longer but you end up with a small hole in the center. You also end up with
a "disc" of metal which has to be ground down before you can install your
new piece.
After using both types when I was restoring my TR4A tub, I actually prefer a
regular drill bit. You end up with a hole in the piece you are going to save
but that is no problem if you pick up a piece of copper sheet you can use to
back the hole when you plug weld it. Just hold the copper piece against the
back of the hole and fill the hole with weld. Grind if off and you have an
invisible weld. I bought a set of 3 different shapes and the plug welding
pliers described below from Eastwood and they worked great.
If you can find one, pick up a pair of plug welding pliers. It's a vise-grip
type of tool that has a copper plate that swivels on one jaw and a forked
hole on the other. You just clamp the two pieces together with the forked
jaw facing you and weld the hole shut.
I have some pictures of me using them to weld up my sills on my website if
you want to see them. Go to the bodywork section and take a look.
http://home.fuse.net/davestr4a
Dave Connitt
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