Plug Welds

[soundcontrol]

Working on my wifes 65 Barracuda. Gotta share this great plug weld trick I learned. When I changed my trunk floor, extensions and quarters on my Challenger I made holes in advance for the plug welds, I drilled or used a hole punch, then weld primer on both panels, the MIG did not like the weld primer so I always used a flat drillbit to remove the primer in the hole first, worked fine, but many moments and took a lot of time.

What I do now is to not drill any holes at first, (weld primer on both sides as usual), then, after getting the panel in place, drill almost thru the outer panel, leaving just a tiny bit to the next panel. Then weld with pretty high amp setting, starting right in the middle, this way the welder is not in contact with the primer at all and is way easier to get a nice plug weld. The burn thru to the next panel is great and its way quicker than making the holes in advance. Of course, only in places you can access with a drill.

[DeathProofCuda]

I will give that a try.  Thanks for the tip!

[gzig5]

Nice trick.  I'll try it.  I usually use a wire wheel or hand brush to remove most of the primer visible in the punched hole.  Had some NAPA zinc primer that splattered terribly. Then got some UPOL zinc that works a lot better.  When it is gone I'll buck up to one of the copper based products.  Live and learn.

[Rbob]

You can always take an awl and scratch out the weld thru primer thru the hole that is pre-drilled or punched. 

I agree weld primer sucks, letting it dry a long time helps some but I always scratch out the hole.

[BFM_Cuda]

Yep, the drilling option works well if you can contain yourself and not drill all the way through....   

I put a little paint thinner on a rag and wipe the holes out. Do a few holes at a time before it evaporates, and store the rag away from the welder when burning them in.

[soundcontrol]

I use this blue weld primer, made my Volvo in Sweden, used in their repair shops, it's the best one I tried, I tried 4 or 5 brands.
Dries quick.

[larry4406]

Here is a link to an alternate approach using a modified drill bit into an almost end mill like profile for cleaning off the epoxy/weld thru primer.
https://www.youtube.com/watch?v=J1jXNfJj2ac

Robert McCartney posts quite a bit on several other forums I frequent (Garage Journal, All Metal Shaping, and Metal Meet).  I've met him a couple times and he is a very nice guy and willing to share knowledge on metal shaping and repairs.

[Rich G.]

I thought it was just me having bad luck with weld through primer. I tried 2 different brands and they both stink. I've been scrapping out the primer from the top hole also before welding. Why do they even call it weld through when you can't!