Hole size for floor pan spot welds...

[64 Dart 270]

When installing new floor pan sections, what hole size do you guys normally use in the new panels where you will spot weld them to the rails?
I've seen some posts that say 7/32, some that say 1/4.
I bought a section of frame rail from a member, bought a small sheet of 22ga steel, scribed the rail location and drilled 1/4 holes for my first practice of plugging spot welds. I'm taking a welding class and wanted to practice on the closest thing to what I'll eventually be doing. Did a sucky job as you can see from the pic. I got another sheet of 22ga today and I'm gonna grind the first practice one off this weekend, make a new one and try again. I know I made too many spotwelds (too close), but my goal here is to get better at plugging holes - making good spot welds.
So what do you suggest fir hole sizes???

 

[gdrill]

I like a bigger hole. That way I can make sure the rail is bare steel and start my weld on it. I then circle my way out to the floor pan. Then I know I have good penetration. A friend of mine actually drills into the rail too so he knows he is getting good contact. Either way, the trick is to ensure the weld is into the rail. It's easy to lay it on top and not hold!

 

[mopowers]

I always go with 5/16". Just make sure to keep the heat focus on the thicker base metal.

Why 22 gauge? That seems awfully thin. Do these old Mopars even have any pieces of steel on them that thin?

 

[pishta]

If you have never chopped a frame rail, you'd be suprised how thin the stuff is in a unibody. I was loooking into 220V stick welders and the guy asked if I was welding oil derricks. I told him just hobby car stuff and he said 110V would be plenty for that thin stuff. ..? with a stick you can get some beefy rods, MIG is different.

...Why 22 gauge? That seems awfully thin. Do these old Mopars even have any pieces of steel on them that thin?

Yeah, any of the original exhaust!

 

[64 Dart 270]

I always go with 5/16". Just make sure to keep the heat focus on the thicker base metal.

Why 22 gauge? That seems awfully thin. Do these old Mopars even have any pieces of steel on them that thin?

I read on a few threads here that the pans were originally 19ga. The pans I've been looking at, I didn't see where tgey said the guage of the steel. Anyway it was a simple choice of I just went to Lowes and they had 22 and the next thickest was 16. Thought using the thinner material would be better practice to ensure I'm also not burning thru.

 

[pauly]

Think my AMD trunk pan is 18 or 19 gauge.

 

[adamm]

I also used 5/16, started my weld on the frame then circled out to the floor pan.

 

[zkx14]

I think my spot weld cutter makes a 5/16 hole. Any I added were at least 1/4. Always start the weld on the heavier metal under the pan and be sure its down against it. I set a cinder block on my front pans to pull down and hold it tight till I got a few welds done. As best I could measure, both original and replacements from Year One were 20ga.

 

[YY1]

go to the u-pull and buy a hood or deck lid from the oldest car or truck there.

practice material

 

[64 Dart 270]

go to the u-pull and buy a hood or deck lid from the oldest car or truck there.

practice material

Thanks all for the great advice everyone!
Ground that piece off today and made a new one so I can practice again at class tomorrow night.
I like the idea of getting a deck lid at the pull a part to practice on.

 

[YY1]

I have a trunk lid skin from a 74 Charger, a hood from a 1980 truck, and an 86 5th Ave to practice on.

All metal on those cars behaves just like my 60's and 70's cars.