Before we could get on with joining the chassis rails together, we had a few other jobs to do.
We had a small problem to sort out first: when tapering the rear section of the left hand chassis rail, we didn't get the sidewall ligned up with the bottom closely enough. The rectangular tube used was slightly concave on the sides, but we managed to end up with about a 1mm step at the joint. This probably wouldn't show on the finished truck, because we're planning on panelling-in the chassis kick-up area, but that's not the point, we would know the fault was there.
We also had the opportunity to try out some bronze MIG-welding wire. This isn't for structural work, the idea being to fill in low areas without using excessive heat. We found the welding a bit fierce, using an Argon/CO2 shielding gas, producing a lot of spatter, and large weld beads. This was possibly because we hadn't had much practise, as it is supposedly used by motor manufacturers to fill small panel joints. By laying on a series of weld beads, about 1-1/2" wide at a time, then grinding roughly flat before filling in the next strip, we gradually covered the whole shallow area. Once covered, we finish-ground all over to smooth things out. We didn't make it dead flat, but left enough material to blend the joint and match the rest of the rail. We are quite pleased with the finished job, as there was very little shrinkage caused by the welding, especially compared to what would have been caused by using mild steel to fill the step. Hopefully we won't have any trouble getting paint to stick to it!
We intend to use a shortened pickup bed - we have an original one that is in reasonable condition, but as everything else is new, we're planning on making one up. To keep the bed as low as possible at the back, in spite of the channeling and chassis kick-up, we will mount it straight onto a rear subframe that will also serve to mount the rear suspension. This will save the extra couple of inches taken up by the wooden supports on an original truck.
The two side members are 3" x 2", laid flat, and the crossmembers are 2" square: the corners are simply mitred (not at 45 degrees because of the different sections), clamped down onto the chassis jig to hold them square, then carefully welded up. We had to cut and re-weld one of the corners to get it square, but we finished up with a nice flat rectangle.
If you've looked at Chapter 1, you will have seen that we made the front crossmember for this chassis at the same time as the other one. Because we were already intending to pie-cut the front rails at the firewall, so they would slope up, the crossmember would be angled at about 5 - 6 degrees. This meant that the centre of the crossmember would already be angled for the spring mount. All we had to do now to make it fit the chassis was to trim the ends to fit between the rails.
We decided to be clever by leaving tabs on the front flange to fit inside the frame horns to blank off the open ends - these were then drilled with a 3/4" hole each side for wiring access. Once the chassis rails were clamped in place on the chassis jig, and all dimesions double-checked, we measured the respective distances between them at the front, and cut the crossmember accordingly. It actually went more easily than expected, and fitted first time!
That's it, we can get on with it now.