131220chassisimageforprojectdev

We had many questions asked what our intentions are with the project. The initial intent was to build 2 917 replicas, mine to be for road and track, and John’s other for track only. But as I started to develop the chassis, it soon became clear that to build 2 repeatable chassis, would require a complex jig. So in parallel to developing the chassis, I started to design the chassis jig. And then to get similar repeatability for the suspension mounting brackets, I designed front and rear suspension jigs.

Then as we started to build the first chassis, it became clear that the jig was working very well, and that we could build repeat chassis to within a tolerance of 3 to 4mm for the main chassis, and 1 to 2mm for the suspension mounting brackets. And with everything designed in Catia, it also possible to offer a bespoke service to customers, to package seat, pedal, wheel, and gear change position to suit individual driver ergonomics.

And we can offer the same bespoke service to provide complete CAD design to package whatever engine and gearbox customers might want. Including water cooled Porsche engines, and in fact any water cooled engine. As the engine bay is designed to original dimensions and in fact we can fit an original flat 12 engine and box. We had one chap who was seriously interested in fitting big block V8, and I’m confident this could be done as well. Would need to investigate side mounted rads, and carry out fluid dynamics, to insure they would work efficiently.

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So to explain the reverse engineering process, and allow people an insight to how we had done this, we had set-up a 40” flat screen TV linked to my Dell laptop, allowing me to show the detailed Catia CAD models. And we also had around the walls of the stand, 10 x A2 display boards with a combination of CAD images and completed chassis and jig photos, to give additional detail. These posters and the CAD display generated a lot of interest, and I spent many hours each day explaining this.

To replicate such a complex chassis had taken me around 2000 hours on Catia, scaling-up from the detailed drawings that are available in several books, and then refining the chassis using the hundreds of photos and videos available on the web, and then further refining once I started to design the suspension brackets.

In total the chassis has 210 laser cut tubes, and approximately 250 laser cut brackets. There are 5 diameters of tubes, which is same as the original chassis. But the primary difference from the original cars is this first chassis is T45 steel tube rather than aluminium. With the suspension (in fact all) brackets being T515 plate, which is the equivalent plate to T45 tube. T45 was chosen as welds very well with minimal distortion, and does not require post weld heat treatment. This was very important due to the many complex joints in a 917 chassis.

 A question that was asked many times at Race Retro was that the original cars had aluminium chassis, and ours (and all the other replicas) are steel. Well the primary reason for this is safety, as the feet in a 917 are ahead of the front axle line. So steel offers better protection on the track and especially road use. We will build our 2 cars with steel, and then we plan to build a 3rd development car with an aluminium chassis. As we are interested to be able to assess the handing differences back to back.

This first chassis was manufactured in 3 stages, which can be seen in the slides in the chassis sub-section. The 1st level being the almost flat base, the 2nd level being everything forward of the engine bulkhead, and the 3rd level being everything rear of the bulkhead, so the engine bay.

As my primary skills are 3D design and engineering and not welding, I made the decision early in the project to have the chassis jig and first chassis built professionally. The other reason for this is I have given myself 3 years window to complete the first car, and if I tried to manufacture the jigs and build the chassis myself, would be more like 10 years!

So for the jigs, and chassis build I selected the Basildon operation of ARRK Engineering, as they had the necessary fabrication skills and facilities to enable accurate jig manufacture, and chassis build. They are also well known in the UK low volume sports car arena, as they manufactured the Noble M600 bodies, and more recently the BAC Mono bodies, along with various mechanical components. And they have done an excellent job, as you would expect from a multi-national engineering company. And in particular I would like to thank Andy Halon for the jig manufacture, and Anthony Maycock for a meticulous first chassis build, including manufacture of the suspension jigs.

The jig and first chassis build went very smoothly; in fact the biggest problem was finding a company to laser cut the 210 tubes. But eventually we located one in Wolverhampton who were very helpful, and prepared to fit my relatively minor project into their large scale production runs. So I sent them 210 igs files from my Catia model, and 3 weeks later had 210 laser cut tubes. And the laser cutters had marked each tube with the individual numbers from my chassis BOM (bill of material), but still took me a weekend to check and sort all the tubes into the 3 layers.

To support each and every tube I designed vertical support plates. In total I would estimate the jig has around 300 tube support plates. All the plates having cut-outs to locate each tube, generally in 2 positions. And there are additional supports that run across car, and these interlock into the vertical supports with 5mm milled slots. So virtually every tube is located into 3D position by a combination of the support plates and the laser cut end profiles.

 Then we started 1st chassis layer assembly. At this stage, I was somewhat nervous as this was the first time to understand if my jig concept was going to work. It looked good in CAD, but as they say the proof is in the build. And the first layer dropped into the supports and aligned almost perfectly, so I was rather relieved and also confident that as we moved into the more complex 2nd and 3rd layers the jig would continue to work and build accurately.

So after approx 3 months, we removed the first 90% complete (less suspension mountings, screen hoop etc) chassis from the jig. We checked weight and came in at 98.5Kgs, with a 48 / 50.5 Kg split front to rear. The first chassis took longer, as we had a few issues with incorrect trims on my CAD files. As at some of the complex nodes, there are 8 tubs coming into a single location. And easy to miss one of the trims, that’s my excuse!

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  • Rolling chassis 3