of Rare Porsche 907 Castings
Restoring vintage racecars can be very
difficult when parts like castings are no longer available as spares
from the manufacturer. In some cases, the castings are made in only
the number required to build 25 to 50 cars plus a handful of
replacements for crash repair.
The original Porsche part
the case with our Porsche 910 restoration. Our original 910 castings
were damaged and repairs would be a marginal solution at best. No driver
wants to race along at 180 mph with a doubt as to the integrity of his
A brand new
spare upright casting was loaned to us for a few weeks. This casting was
from a 907, which was an improved part with improved geometry. We knew
that we would have to go to great lengths to reproduce the rear
uprights, so we chose to put the time and money into the revised 907
part and go for the improved suspension geometry that would result. The
907 was better than the 910 – not a difficult decision.
We only had
a left side part and we needed the other side. We also wanted to make
absolutely sure the shape was copied with fidelity and all of the
critical geometry was preserved. There are no easy technical references
available for working on such rarified limited production machines of
automotive warfare. The part we had in hand was over 33 years old and
Porsche has moved on to building SUV's.
The cast made from the digitized data.
part was beautiful and exquisitely complicated. It also had no flat
surfaces or easy features to make a geometrical reference from. We
visited several foundries and pattern makers and they would scratch
their heads. No one agreed on exactly how the part was cast. All agreed
that the skill level of the original craftsman was extremely high and
that it would not be easy for a modern pattern maker to reproduce such a
part. This was getting complicated fast.
We purchased a
MicroScribe 3D with the idea that we would digitize the original part.
We would turn this four pound hollow magnesium piece of sculpture worth
the price of a new street car by itself, into a database that would
allow us to make more parts using more accessible modern machining
technology After some careful consideration and strategizing, we
embarked on a precise digitizing effort using the Microscribe. We used
Rhino to generate all of the outsidee surfaces of the casting.
It was not
practical to knit all of the surfaces into one surface that could be
imported into Solid Works and manipulated – this part was far too
complicated for such an approach. Instead, we knitted as many of the
surfaces into each other as we could and imported the IGES surfaces into
Solid Works as references
The part in SolidWorks.
also allowed us to hollow out the part in such a way as to maintain a
very thin 5mm casting thickness everywhere inside. With a few keystrokes
we were able to make the mold parts as derivatives of the hollow spaces
inside the part. Later we would make the mirror images of the rear
upright part and the molds and send the final IGES file to Dave
Aspenwall of Marty Manufacturing.
Mazak CNC machine, Dave took huge blocks of pattern plastic the size of
Texas, and machined them down to perfect polished pattern parts and core
box molds. Being a pattern maker by training, he was able to help us
make some small changes to the patterns and cores to ensure success at