Very nice as always James. I have been missing your updates.
Why do you use the L section to join the cill reinforcer to the floor of the cill? If I'm recalling correctly originally the 3 layers of cill were spot welded together, is that difficult to replicate?
It's a combination of having good metal to weld to which then retains the original strength of the box section once it is back together, access and a bit of future proofing in that I am using zintec steel everywhere.
Hello children, it's time for one of uncle James' dodgy drawings!!!
On the left is the original sill structure, the blue being the inner sill, red bring the diaphragm, and the green being the outer sill, welds are illustrated with black dots. You will notice that the original sills have a lip/channel on the base then a flat section which the original diaphragm is spot welded to. When you remove an original outer sill you tend to have to cut this lower folded section of the diaphragm off (it's normally rusty!).
On the right hand side shows my club sill fitting, you'll notice that they don't have the lip/channel, Alun will correct me if I am wrong but I believe this is due to the costs and relative complexity of adding it in. This does mean that the whole sill sits about 6mm lower (if you want the profile to look correct), this is not an issue. As the inner sill is almost always rotted at the ends so I cut this off and replace it with a club inner sill repair panel (panel F on the spares list), illustrated in pink on the drawing, this can be seam welded to the inner sill. This also gives you a good clean seam to plug weld the lower section of the outer sill to. As you have cut off the original diaphragm lip a new one will need to be welded on, I use a single length of strip press braked to just over 90 degrees, plug welded on to the base of the inner sill (as you won't have access to weld it to the base of the outer sill) then seam welded and plug welded onto the diaphragm (light green in the diagram). The club outer sill (purple) can now be fitted by seam welding along the top and plug welding to the inner sill repair panel. I haven't illustrated the jacking point's or the seatbelt mounting reinforcement, they will need to be either replaced or extended to meet the new inner sill, I would recommend seam welding these in place.
If you need to replace a section of the diaphragm, use a club one as they line up correctly, you can cut the original diaphragm off half way and either but or lap weld the new club one on, you will still need to cut off the lip and use a folded section as per above to retain the correct profile on the sill.
If your welds are good then you won't have altered the structural integrity of the vehicle by doing this.