|
Graham, glad you like how the “exo-cage” came out. It was a unique challenge as fabricating a cage in any 7-esque vehicle always is. Most look at any car and think that you can just start cutting/bending/welding and Voila, you have a cage. The problem with our cars is that the frame rails and aluminum body skins don’t allow for real attachment points to anything substantial. I say “substantial” as if there really is anything “substantial” on a car that has 3/4” and 1” tubing as it’s main structural elements!
First, I had Graham sit in the car and determined how tall the main hoop needed to be. His original rollbar was 3-1/2 to 4” too tall and looked awkward. We agreed to shorten it a bit, but his main concern was having the finished product look good on the car. The correct rake, length, supports, access to the and removal of the fuel cell, ingress/egress, etc.... Not only function, but aesthetics as well.
Next came some exploring and seeing just how his car was constructed and what was or wasn’t hiding beneath the interior and exterior aluminum body skins. No big surprises here, just 1”x0.095” tubing. I had some threaded sleeves that I use on the inboard side of upper and lower a-arms. They are 3/4” OD, 2” long and are tapped 1/2”-20. Once a design was figured out and where the sleeves needed to be installed, it came time to start drilling. First a 1/4” pilot hole, then a 1-1/2” hole saw gently through the aluminum skin. After that, a 3/4” hole in the outside of the frame tube and an 11/16” hole on the inner side. Each one was turned on the lathe to the correct length and then down to 11/16”. 0mce all of the slugs were fitted, it came time to weld but there was a bit of an issue. The original builder filled the space between the inner and outer aluminum skins with some type of styrofoam sheet and I was afraid of a smoldering fire. No worries though, some wet rags and air helped the whole welding process.
After the slugs were installed in the chassis it was time to start figuring the next piece of the puzzle. How to attach the tubes to the threaded sleeves. In order to do that, I cut some 1-1/2” solid bar stock to 2” in length. Those pieces were turned to have a 1” hole bored in them 1-3/4” deep so they have a wall thickness and end thickness of 1/4”. Some socket cap bolts attach them to the slugs.
Now the fun begins, it’s tubing time! Cutting tube, a bend here, a bend there, lots of notching, a whole bunch of grinding/fitting and welding it all in place. It sounds like it went quickly, but it took a bit of time to get right. Then, after it was all welded on the car, the moment of truth. While designing the cage, I wanted/needed it to be removeable in order to fully weld the body-side of the attachment pieces. With 2 people helping, the whole cage was able to be lifted off the car!!!!! Another hour of welding and cleaning up with a wire wheel and it was ready to slide back on the chassis. I was worried about the final welding causing a bit of distortion, but it fit with no issues.
The nice part about having the cage removeable is that Graham is planning on fabricating a new aluminum scuttle over the winter and once he begins, he won’t have to continually work around it. Once the rough shape and size is determined and fits under the front radiused cross bar, it can all be removed.
I appreciate Graham reaching out to me to work on this project for him. It also gives me some inspiration for the next 7 project that I build. I would like to eventually have a fully caged trackday/hillclimb 7, but that’s years down the road.
Thanks Graham and good luck with the evolution of your car.
Be safe,
Dan
_________________
Dan Lipperini Jr
www.RaceLabz.com
|
Login
Register
FAQ
Members
