Daily Archives: June 21, 2018

How do I bolt the body to the frame OMT

Yep, that issue again. Every iteration of the frame requires a new solution to mounting the body to the frame. This version is no exception. The issue this time is the frame rails and the body mounting flange literally have only a passing relationship, as in the frame rails pass under the front corner of the body for a few inches and they never see each other again. Now this might make for a great movie, but it makes for a crappy car.

This problem arose because to reduce flex in the frame I had to remove all the bends to get the frame to tuck up under the body. The mounting flange on the bottom of the body is 27″ wide at the firewall, spreading out to 34″ at the pinch of the cowl and then a nice straight run to 34½” where the back of the body meets the bottom 38½” behind the firewall. The topside of the body is considerably wider with the windshield base across the top of the cowl pinch being between 38 and 39″ depending on how you measure it, and the widest part of the body just a hair over 45″ right about the same distance behind the firewall as where the back meets the bottom. This results in conflict between straight frame members and running the frame under the body instead of through it. If this was a Locost instead of a bucket there wouldn’t be a problem because that car has vertical body panels that pop-rivet to the frame. On a Sprint-T the frame goes around the body so the body can be painted and installed after the frame is fully finished. The conflict arises anew when the ugly triad of light, strong, and cheap also conflict with “looks pretty”. So we have to make the mount light and strong, and cheap, and pretty as it runs from under the car to where the frame rail ended up, and what I’m getting is either light and strong but ugly and expensive, strong and cheap but heavy and still ugly, and everything pretty is either heavy, weak, expensive or all of the above.

The sticking point is the frame rail on the bottom runs from 30″ wide outside to outside at the front hoop to 48″ outside to outside at the rear hoop 58″ away, with the front hoop just outside and in front of the firewall and the rear hoop behind the rearmost part of the body. I tried to move the bottom rail in closer at the back but the diagonal that runs from the front hoop to the bottom of the rear hoop runs into the body. So far the best compromise is 0.060″ wall 1.5″ square across where the back meets the bottom of the body and forward under the body until it meets the main rails, and welding the floor to the top of that. It’s ugly with a Capital UGH and the aero is Not Good, but it’s strong and light and reasonably cheap.