Today I got started on a job for a guy I have only just met called Ran, but he is a ridiculously good tattooist. Check out his Facebook page here.
Ran has bought a crazy looking VolksRod, there are a few pics of it here on the Aussie VeeDubbers Forum. This beastie of a car was never registered here in Victoria by the original rodder, and once Ran had it inspected it was obvious some of the cut and shut work wouldn’t pass muster.
The engineering signatory that inspected it gave Ran a long list but one of the biggest hitters was the front axle beam extension. This was knocked together pretty roughly and the engineer wanted it put back to standard (no chance of that), X-rayed or remanufactured. Personally I wouldn’t run this part on one of my cars, so I offered to build a new one for Ran.
There are a few existing designs around; you can find them with a Google Image Search. The general idea of these existing beam extensions is pretty sound, I think, and with some thoughtful design work they are ripe for cutting out via CNC waterjet or plasma cutting.
So, I figured I would work along the same lines, in terms of the general approach to the extension, but we’d maintain the extension and raise dimensions of Ran’s car, which is definitely not common. Eight inch extension with 2-2.5″ drop is common, Ran’s is 6.3″ extended and 4.6″ dropped. Since the steering and sheetmetal have already been set up for this axle configuration it seemed stupid to undo any other good work already completed.
So I picked up the extension from Ran and took a bunch of measurements from the front end before retiring to the computer to start laying out the general shapes.
The process I followed is something like this:
- Maintain the position of the beam mounting locations on the adaptor (in the form of circles) in the software package
- Join up the circles with nice curves
- Check there is enough space to fit the mounting bolts
- Check there is enough space or at least a logical assembly sequence so you can actually weld it all together
- Repeat until satisfied
I use Trimble Sketchup (formally Google Sketchup) which is free and has a fast learning curve. I really should be doing it in some fancy-arse 3D CAD modelling package but I don’t want to pay for one, nor go through the pain of learning how to use it. I can get someone on Elance to do the modelling for nix, and they’ll do a better job than me anyway.
Here is a pic of the extension model I finished today:
The general ideas are as follows:
- Everything is made from 6mm plate – single material (keep cost down)
- The profile plates are all identical, which should make them cheaper to be cut out if I go waterjet or plasma
- There are two horizontal plates that run through the profile plates to stiffen up the structure
- There are three other plates that tie the horizontal and profile plates together
So the next steps are:
- Start putting in some weld details
- Get some Finite Element Analysis done to check whether the design and the welds will be adequate for the road loads expected. For example, maybe we need to use 8mm plate, or we can get away with stitch welds rather than long runs. This is specialist stuff these days, so I’ll subbie this out.
- Make any modifications needed and repeat the FEA until we are happy the design is strong enough to handle the road loads.
We’ve still got to account for VSB14 which will form part 2 of this build thread. Stay tuned…and head over to the Garage Engineering Facebook page for the beam extension build to see more pics and comments.