[MARTINSR]

Here is a tip that I randomly just posted on facebook from the Hotrodders forum. I can't believe I posted it there 16 years ago! Wow time flies! It may say "floor welding" tip but it really is for just about any time you are plug welding. At least for how you lay the weld "fast and hot."

“Basics of Basic” Floor welding tip
By Brian Martin

This tip isn’t only for welding in floors, it can be used anytime. But it works the best when plug welding a thin sheet metal to a thicker brace, frame or whatever. Welding trunk floors into late model cars that have been rear-ended is common practice these days. Just a light hit on the rear of most late model cars will result in a badly crumpled floor and a frame rail or two needing to be replaced. After welding in many of these cars and always having a problem with keeping the floor nice and flat against the rails while welding, I came up with this trick that really works well for me.

I used to lay the floor and align it, then mark the underside around the edges of the cross members and rails with a sharpie. Remove the floor and punch all the holes around the edges of that line I made so I could plug weld the floor to in. I have some real nice punches with a long reach and I would drill the ones I couldn’t reach. This required cleaning up the back of the holes of burs and spraying some weld thru primer and what not, a lot of prep work. But I thought I was slicker than snot doing it this way, the thing sat back in there with a row of holes all the way around right in the right place and it really looked good. Until I started welding, no matter how nice I could do a plug weld, on these floors the darn thing would always come up a little around the holes as I welded and it looked like crap once done.

The solution is not only produces a better end product, but it is much easier. What I now do is to align the floor into place. I will hold the floor in with a sheet metal screw here and there just as before (later welding the hole up) but now I put them where ever I can draw a straight line from screw to screw or at least be able to know exactly where the rail or cross member is beneath the floor. I then mark it ON TOP of the floor where the holes need to be to plug weld it in. So, I have a nice floor pan with no ecoat removed, no grinding, no drilling, just a nice new pan sitting there on top of the rails. The rails by the way were cleaned with a Maroon Roloc surface-conditioning disc and a weld thru primer was applied.

I now drill a few holes thru the floor pan and a little into the rail. I use a killer spot weld drill I get from our fastener supplier (Winzer). They cut a shallow hole so I don’t cut thru the rail, but they have a pilot tip that is like an 1/8” drill to keep it where I want it as it starts. And they drill VERY fast. They are 8mm (about 5/16”) in diameter.

Soooooo, these few holes are now drilled, I have perfectly clean metal in the rail to weld to, the metal is a little thinned by the drill so I can get good penetration with a nice fast, hot weld! I weld these welds very hot and fast leaving a super clean flat weld on the top side. PLUS, the weld is so hot and fast that the surrounding floor pan doesn’t lift up from the heat as it did before. After a few welds, I drill a few more holes and weld them up, and on and on until it is done, skipping around side to side and even walking away and doing something else now and then to let it cool off.

I use this same method on radiator supports to the frame, when ever I am welding a thin metal to a thicker one. It produces a cleaner plug weld than anything I have ever tried when welding a thin metal to a thicker one. Plus, less corrosion protection is burnt off.