At this point, I now have the pattern for the new shape of the frame, ready to cut out of 1/8 inch steel plate. How I got here from where I was last time, involved some important decision-making.

First I needed to determine where the front suspension mount would go, relative to the frame. And for that, I needed to know how high the truck would ride, the decision point where I left off in the previous post. I wanted the truck to ride a little lower than stock, but I was concerned about suspension travel and as it turned out, this concern was well-founded. In the end I achieved a two-inch drop, but the suspension will need to be somewhat stiff to make it work, and even so I had to draw in an indentation in the underside of the frame to allow for a little extra upward travel. With Erik’s help, I simulated full-range travel of the axle mount in the various link bar positions, to determine where the top of the mount would end up relative to the frame. This helped me to shape the indentation such that all link bar positions result in roughly the same amount of suspension travel. With this out of the way, I had a mostly-complete design drawn for the frame.

For today, the next step was to make a template from foam-core, which is easy to work with but durable enough to trace around it for each of the 4 identical steel pieces necessary to rebuild the frame. To transfer the drawing accurately, I used a large sheet of paper from a roll, taped it in place on the dry-erase surface, and traced the outline from my working drawing onto the paper. I then cut out the shape from paper, traced around it onto the foam-core, and cut it out leaving an inch of border all around. The next task would be to finalize the exact shape of the mockup, especially at the ends where it would mate to the existing frame.

Or that would be the next step, except that I was having trouble getting an accurate match-up against the edge of the frame. The problem is that the width of the frame rail is not constant. It bulges out in some places, and is narrower in others. This was probably not intentional, but it isn’t really a defect either — it’s merely an effect of how the frame is manufactured (it’s punched out in a press). The bulges were getting in the way, and so I cut the rails to an even width before continuing.

Fast-forward past a bunch of marking, tracing and transferring, and I finally now have the official new shape of the frame mocked-up in foam-core. I cut out the template and held it against the frame, and the transitions between the new frame and the old are exactly as I want. As a final act this evening, I traced the first two of the four pieces from the template onto the steel plate, and I’ll be ready to cut them out tomorrow. These will be the outside pieces — I may make the pieces on the inside of the frame a little longer, to stagger the joints a bit and make them stronger.

Pictures from the past few days are forthcoming in Planning the Suspension, for right now there’s just the one picture in Frame Modifications showing the finished template and the tracings on the steel plate.

Many thanks to AustinEV’s Aaron Choate for stopping by to help out and take pictures.