Spot welding techniques.

[Pete Rodder]

I'm in the process of replacing a half floor pan section on my Beetle roadster pickup project and am having major problems trying to spot weld using my mig.
The Beetle chassis is 1.5/2mm thick and the replacement panel, that I'm trying to attach to it, is 20/22 gauge. Both mating surfaces are clean and shiny(as is the earth) and I have drilled a series of 3mm holes in the panel to weld through.
I have a new Clarke Pro 90 welder using Co2. I have tried both #6 and #8 wire on all sorts of settings but am having mixed results getting a strong reliable weld - the weld is not very clean and keeps breaking away from the chassis.
Present settings are: #8 wire, Current 2 Max, Wire speed 7, point wire into the middle of the hole and squeeze trigger for 2 seconds.
"HELP!"

 

[Pete Rodder]

Just read the 'Plug Welding' article and it looks like my holes are too small, so I will go and drill them out to 7mm and try that. Would still appreciate advice.

 

[Chickenjohn]

Drill holes up to ~8mm, clamp the top face very tightly to the lower face and make sure metal is shiny and clean on both pieces. Then start weliding in the middle of the hole and make a little spiral out to the top piece. Use a higher setting than if you were butt welding the two pieces together.

It is very important that both pieces are very clean and tightly clamped together.

 

[Pete Rodder]

Thanks for the info.
I opened up the holes to 7mm, wound the wire feed back to 5 and increased the gas flow - bingo, clean strong welds, job done!