On Sat, 02 Dec 2017 11:26:01 -0800, etpm wrote:

I don't have much experience spot welding. I am looking at an assembly
that is made from 3 laminated pieces of 1/8" mild steel. Since I
designed the assembly I can choose the fastening method and was
wondering if the parts could be reasonably spot welded together. The
assembly process would be to first weld two parts together and then
weld the last part to the now 1/4" thick assembly. I am also
considering blind rivets and screws. But spot welding would obviate
any drilling or tapping. And I was thinking someone here would have
the practical experience to let me know if this scheme of mine is
practical.

The Harbor Freight #45690 spot welder doesn't handle that much, in my
experience. I've spot welded a lot of .1" + .1" assemblies with good
results but .1" + .125" just tacked instead of welding, and .125" + .125"
didn't stick at all. The .1" was cold-rolled and plated steel; the
..125" was hot rolled and I probably didn't get enough of the mill scale
off to get good enough conduction.

The https://www.harborfreight.com/240-vo...der-61206.html
item is similar to the #45690. #61206 is rated at 2.5 kVA. With
twice that power you probably could weld .125" + .125" reliably and
quickly, but if you need a good strong three-layer weld I imagine
8 to 10 kVA would be needed. Do you have any factories or shops near
you with a good sized spot welder so you could try out your assembly?

--
jiw