Now that the vertical bulkheads have been tied in with the beltrail, it was time to tie in the beltrails with each other, around the rear of the car, underneath the rear windscreen aperture. By adding depth to this area, it massively increases torsional stiffness, and gives us an attachment point for the engine cradle/suspension/subframe structure.
The profile of the beltrail is too complicated to reproduce and keep that profile going around the back of the car, it does not need to serve the purpose that the beltrail does, as in hold any interior trimming pieces etc, so a simple box section is easier to fabricate and install. The transition from beltrail profile to simple box profile is done through simply welding endcaps to the beltrails at an oblique angle, which will allow the box profile to be welded on to these. This is done at the point where the rear window meets the beltrail at the rearmost point.
Drivers side:
Passenger side:
Justin has decided that the entire shell, including the roof is to be deseamed (and I thoroughly love the deseamed look of a Mini!!!). So prior to fabricating up the box-section that goes underneath the rear window, the rear seams where the box-section would cover has to be welded up. When deseaming the rear seams, I weld the seam from the backside (inside) then grind off the flanges from the outside, leaving a flush body line which is now fully one piece. You have to ensure that the weld on the inside of the seam covers the entire join, and has adequate penetration on both sides.
Inside passenger side:
Outside passenger side:
Inside drivers side:
Outside drivers side:
Also somehting else that needs to be done, is to fill in the fuel filler hole. As mentioned above, the fuel tank is now in the front bay, slightly offset to the passenger side to counterract driver weight. The old Mini fuel filler hole is now redundent. Its simply a case of profiling a piece of sheet on the english wheel until it is the same profile as the body (a complex curve in two planes) and then cutting it to size and then tacking it in prior to flly welding:
Ground flush:
Good penetrations on the inside:
We are now ready to fabricate the rear upper horizontal bulkhead. It is a complex shape, with the transition curves on the flanks leading into a larger radius curve along the rear window, and the depth and fall of the panels varying as they move from sides to back. I decided to build this complex shape in four parts - an upper and lower section and split in the middle left and right. The upper and lower pieces will overlap and be plug welded to each other through the front face, and then butt-joined to each other where they meet in the centre. The pieces will be joined onto the body by lengths of seam-weld at regular intervals.
I started on the passenger side upper section, folding a piece of 1mm cold rolled steel at right angles. I then worked the lip of the profile in the shrinker/stretcher until it conformed to the profile of the body. Ths took some time to get right as any gaps to body will make it harder to weld and potentially compromise the structural integrity of the monocoque. This is what it looked like:
And this is how it sits against the inside of the shell, welded on with holes punched through to plug weld to the bottom section. Note the crossbracing still in place to ensure that the shell shape and profile is unaltered as we work on the rear bulkhead:
And good penetrations to the outside of the shell:
Drivers side:
The lower sections were more of the same, except upside down. One the lower sections, because of the altering depth to the body, used CAD - Cardboard Aided Design - to get the correct profile and shape, prior to cutting and bending in the panbrake. Because of the depth to body being significantly larger than on the upper pieces, the curve had to be cut out and not profiled as you would in the shrinker/stretcher. A simple lip was turned up and dreesed using the hammer and dolly method:
And then trimmed and welded in position, and the plug welds welded through the face, to essentially make the two pieces one:
Good penetrations through to the shell:
And when the drivers side was done, this is what the finished bulkhead looks like - it makes this rear section extremely strong and now the crossbracing can be removed as well. From this photo you can see how complex the shape was to imitate and get right:
Plug welds ground and the transition with the beltrail dressed:
Once again good penetrations to the shell:
Now that this is done, this horizontal bulkhead now enhances the structural performance of the monocoque, and can be used as an attachment point for the rear subframe assembly.
Cheers,
Tricky
