Metal Work - Welding sheet metal
Added May 2007
How-to, Tutorial, Step-by-step, Technical Article
Restoring or building any car is a series of steps, each one building upon the other so
that each step can only be as good as the one before it. While there are no unimportant
steps, some are definitely more noticeable than others if they are done incorrectly.
Every restoration that passes through MCR needs some sort of sheet metal work that involves welding in new pieces
so we thought we would show you how we join body panels together.
First off, never overlap seams, always butt weld. Second, never stitch weld, you'll warp
the panels beyond repair. The proper way to do this is to do a series of tack welds that
are quickly quenched, not by water, but with an air nozzle.
Whether we are replacing a body panel with a new aftermarket piece from Year One or a
used part from a donor car, the process is the same. We start by cutting the panel
oversize so there is enough overlap to hold it in place with Cleco fasteners. A seam is
then made by cutting down the middle of the overlap with a West Cut 4 inch cutoff wheel
and peeling back the remaining strip of metal. You can now place a tack weld between the
Clecos but be very careful to make sure the panels are perfectly even. Use a small
screwdriver and the tip of your finger to line things up before you place each tack weld.
Now simply place a weld about every inch, alternating sides and quenching with compressed
air, until you have the entire panel in place, pulling Clecos and extending the cut as you
When you have made your way around the entire part, just do it again, placing another
weld in between each one you have done. It's a good idea to skip around as you go so you
don't build up any heat in one spot. When you have finished this round, do it again.
Resist the temptation, though, to get lazy and not quench or even worse to try to do short
stitch welds. Even though the panels are feeling pretty solid at this point, it is still
possible to cause warping.
At this point, your gaps should be about a quarter inch apart. Before you close up the
gaps on your next time around, grind the tops off of the welds with a 24 grit disc. Don't
try to grind them flush. You are just removing excess weld to make the final rounds
Closing the gaps involves placing three quick tack welds in succession. No, this is
not stitch welding. Don't even think about running even this short of a bead. It might
help to think of it as tack welding the tack welds together. Do every other gap first and
then come back around to finish your seam. Don't forget to quench.
The last step is to grind down the weld with a 3M reinforced weld-grinding wheel. Grind
it almost flush, maybe leaving a very slight crown. You must avoid touching the panels
with the grinder as they can get too thin really fast using this tool. It's better to
leave just a little extra rather than go to far. If you discover any pits or missed spots
while you are grinding, just go back and touch them up with the welder again.
Your finished seam should look pretty much like this. It wouldn't be a bad idea to run
a good wire wheel over the entire length of the seam just to be sure that any small pits
that remain are completely clean before you move on to finishing with lead or body filler.