Another reason for designing the ribs with AutoCAD is that I would have a computer file that could be sent to a fabricator to have the ribs cut out either by laser or water jet, instead of me buying the raw materials and cutting and shaping the ribs by hand. Before I did that, I wanted to make sure that the design would work, and also to see how it would look. I printed out the drawings, glued them to ¼" plywood, cut them out and fitted them into place. Although not shown here, there will be a gap between the tilt shell and the aluminum rib. The gap will allow space for the rib mounting tabs to be bonded and 'glassed to the shell.
Once I had the templates made, I laid them out on a 1" grid pattern and traced the curve onto the grid. From here, I measured the location of the curve along the horizontal and vertical axis every inch. This gave me the coordinates that I input into the AutoCAD software to create the curve. Once the curve was created, I added the details. The last picture is the completed rib in AutoCAD.
To make the finished aluminum ribs, I decided on drawing the final design using CAD software. In order to input the curves into the computer, I needed to make more accurate templates of the tilt shell where the ribs would be attached. There are four rib sections on each side, plus one transverse rib, for a total of nine rib sections.
Being that the tilt shell is very flimsy by itself, I built a raised jig which keeps the shell in the proper shape while I work on it. If left to lie on the floor, it will droop and the fiberglass will take a set. This also insures that the ribs will be made to the correct contour and also hold the shell in the correct shape when bolted up. After putting the shell in the jig, I took the opportunity to let it sit in the sun to warm up and let the fiberglass "relax" and get used to its final form.
I wanted the ribs stiff enough to keep the tilt shell supported, and also to be able to take the force of the linear actuators. I decided on a 3" deep rib, and started laying out the ribs in cardboard. The ribs will start at the front of the tilt shell and be parallel with each other in the hinge/grille/actuator area, and then flare out to follow the original hood line. They will continue rearward until just ahead of the firewall, where a transverse rib will run parallel to the firewall and tie together the two front-to-back ribs. These photos show the early rib layouts in cardboard. The third photo is with the tilt shell positioned back on the car to check the clearance for the transverse rib. The rib will be just forward of the firewall extension "horn". The electric suicide door latches that I installed in the firewall horn will protrude through the horn and into a corresponding hole in the rib. The latches, along with the linear actuators, will keep the tilt shell closed and locked.