3 replies to this topic

[srx600]

I am slowly removing the near and offside floor pans, I decided to retain the tunnel and bought pre-assembled floors from m-machine.

I have nearly removed all of the old floor and need to decide what is the best technique for welding the new floor to the existing tunnel. There seems to be several options. 

1. Joggle the new floor pan edge and seam weld along both edges, I can see this being quite strong but could form a rust trap if water gets into the gap. It can also be a 1mm or so out so accuracy isnt quite as important.
2. Lap weld, which is pretty much the same as above but not quite a neat.
3. Butt weld. This needs both pieces to be accurately cut. and then held with intergrips whilst tack welded

3) is my preferred approach but I am not sure how I can make a straight and accurate cut down both edges of the join. The only approach I can think of is to assemble and pin everything together with 20-30 mm overlap, then clamp a straight edge along the floor down the centre of the overlap and then run a 1mm disc down the straight edge. I have an air saw but I cannot see me getting a good straight cut with that.

 

Any other ideas or approaches ?

Edited by Ben_O, 20 March 2018 - 04:41 PM.

[minimans]

Use the lap joint joggled or not, unless your an experienced welder it's going to be a hit or miss affair as to whether you will get a good strong bond, with the lap joint you have twice the weld! also if you use a good weld through primer the space between the laps will not be a concern.

[Ben_O]

I would always go for the butt weld.

 

I tend to lay the new floor in so that it overlaps the existing metal by at least 1" and then once it's clamped in place accurately and you are happy with everything, mark the edge of the overlap on the existing floor from the edge of the new one with a pencil (sometimes I spray some primer down in that area so that the pencil shows up clearer)

Remove the floor again and cut along the pencil line with a 4.5" 1mm cutting disc in the grinder. I find that you can get a straighter cut by running the disc along the line carefully without going deep enough to cut through. This will create a channel for the disc to sit in when you do make the cut right through and stop it going off path.

Once you have they panel cut in. put the new floor back and clamp it up as before. If you have it right, you should have a 1-2mm gap between. It is important that you have at least 1mm. If they edges are touching or the gap is too small, the panel will buckle when you weld it and penetration will be poor.

I usually have a 3mm gap between but I wouldn't recommend this unless you are experienced with the Mig as it has the potential to blow holes everywhere very easily. If done right, this will provide a very strong join.

I have a nice big piece of 6mm thick copper sheet which I often clamp underneath the join on the opposite side to welding. This provides a very good heatsink to minimise heat and distortion and also acts as a great backing piece to help get the weld in nicely without blowing through.

The other bonus is that it makes for very tidy penetration on the back instead of being blobby and uneven.

 

Take a look here to see what I mean. This is Inner sills I did on a Mini recently and shows the process

 

http://www.theminifo...f-wight/page-10

[srx600]

Thanks guys, food for thought. I have been welding for while but not done much in the way of panel work. I think I will practice with some cut offs before making the final decision.