Classic 911 Air Control Box
For many decades this air control box distributed air through the cabins of various Porsche 911 models.
This ingenious designs is entirely modular, employing 5 base parts which in different configurations make up a left and right hand assembly consisting of 7 components each. Unfortunately neither this assembly nor any of its components are available from the manufacturer. Good second hand ones are rare and expensive and typically sold as complete units, often with defects which only become apparent when disassembled.
It is wasteful to buy a whole replacement unit when only one or two of the components need replacing but aren't available individually. We set out to solve this problem.
There are two flaps inside the assembly which are notorious for breaking.
The challenge here is to make them as strong as possible while adhering to the original dimensions.
The originals were made from a bacallite-like material and, while being extremely rigid and heat resistant, it also means that they were brittle.
Porsche clearly over-engineered this mechanism for maximum strength and durability so why would it break? Under normal circumstances these parts would last forever and we see instances where they are as good as new.
However over the course of half a century there are some moments in a car's life when circumstances aren't normal. It often has to do with an accident which causes a small fracture which takes years to propagate to the point where the part finally breaks. The most common cause of failure however is disturbance during restoration. More often than not these parts have been weakened over time but still function, only to finally fall apart when removed from the vehicle.
With this in mind it's essential that the replacement parts are not only rigid but also durable and impact resistant.
This eliminates many of the commonly used thermoplastics as well as almost all the resins currently available.
The complex nature of this assembly and the relatively low volumes in which it will be produced means that MJF printing is the most sensible option. The material of choice is nylon PA12 which is tough, heat resistant and less likely to become brittle and crack over time than the original. It also produces parts of high dimensional accuracy which is particularly important in this case as only one or two components will typically be replaced, meaning that the restored assembly will almost always consist of a mix of original and printed parts. So our replacement parts have to fit each other and the originals perfectly, every time.
Step one
3D scan all the parts in high definition. Some of our samples had bits missing but fortunately there's a lot of repetition between the parts so we could fill in the gaps in CAD.
Step two
Design new parts from the scans and from measurements of the original. Fortunately the sizes and shapes of the parts made them fairly easy to scan and all the details were picked up accurately including the locating indents and grooves
The genius behind this mechanism quickly became evident. The centre part which on face value is a fairly complex shape, turns out to be a mirror image of itself along 2 axes which means only a quarter of it needs to be designed and then mirrored twice to make up the complete part.
This also means that there's no wrong way to start the build as the cornerstone part is always oriented correctly to slot into the rest of the assembly, which is also made up of parts that are mirror images of themselves. What a shame that such a clever design has to be hidden deep inside the body of a car.