A bit of advice please.

[reno]

So, I'm new to welding and as my first project I need to make some repairs on my cars floor pan (drivers foot well) and sill.

I've stripped the interior out to get to both side of the rot and have made or started to make most of the repair sections out of mild steel but I've got a few questions to ask before I cut the hole in the floor or put the welder anywhere near the car.

I was originally intending to make my floor pan repair with a set edge so that I could plug weld the repair section onto what remains of the original and them seam weld up both the top and bottom edges. Is this a good idea or should I butt weld the repair section in?

Any and all advice greatly received.

Cheers reno

 

[rusty69bus]

in general a repair piece should be........like for like, if it was one piece of steel you should seem weld alround

 

[piman]

Hello Reno,

I prefer to see a butt weld as there is less chance of trapping moisture, or in your case, if I understand correctly, you are going to weld both edges of the overlap afterwards which is double the length of weld?

Alec

 

[engybenjy]

Anything for MOT on a car 'should' be seam welded.........Its the way ive been taught to do it and my MOT man insists on it
HTH

 

[piman]

Hello EB,

not strictly true, if the panel is being attached to where the original was spot welded, the repair panel also may be spot welded. All inserted patches should be seam welded.

Alec

 

[reno]

Thanks for the replies guys! I don't think I've explained myself properly so I'll take some pictures over the weekend and post them up.

@ piman: I was thinking of producing an offset lap and would seam weld both edges which would mean effectively doubling the length of the weld. I'm not too worried about the lip that this would create as it will be underneath the sound deadening what I am more concerned about is the potential for the floor pan to distort with the heat.

Thanks again, reno

 

[weldingscotty803]

depends how big the repair patch is. small 100mm square should be ok if you dont concentrate in 1 place too much.

 

[reno]

Erm, its gonna be a tad bigger than that... From memory its about 300mm wide (edge of floor pan to centre of chassis rail) and runs forward to the edge of the front edge of floor pan at about 350 - 400mm.

 

[stormin]

By overlapping the patch you are effectively doubling the thickness to be welded. This means a higher setting on the welder, more heat, and more chance of distortion. Doing both sides, whilst good for sealing, just doubles the chances of heat distortion.
If you cut the patch to the exact size and butt weld it'll produce a better finish, you can grind both faces near flush afterwards. Work in short lengths at a time and come back again once cooled. Apply a heatsink nearby if possible.

 

[weldingscotty803]

just do 1-2 inch runs, alternating each fouur sides. leaves enough time to cool in between, put a tack weld every couple of inches

scott

 

[reno]

Ok, thanks for the advice guys.

By the sounds of it using an overlap is likely to give me more of a headache so I'll ditch that idea and butt weld the repair in.

Thanks again!

 

[engybenjy]

Hello EB,

not strictly true, if the panel is being attached to where the original was spot welded, the repair panel also may be spot welded. All inserted patches should be seam welded.

Alec

Sound. See you learn something everyday!