You might be wondering why we obsess over something so elementary as an object being flat. It’s pretty simple – mostly, when you are sending out your old factory cases to be machined back to spec, what they are doing is restoring the flatness of the case. Shops like Ollies, like Competition Engineering (Walt Watson) are mainly concerned with making the case mating surfaces flat as well as the cylinder spigot faces flat. Heat and age conspire to warp these surfaces ever so slightly.
But my premise is that they were never really that flat to begin with. As I have pointed out before, factory tolerances are pretty loose.
Also, the method these Porsche shops use to restore flatness is pretty primitive as well – they use a flat honing stone that is scraped against the surface to restore flatness. It comes back fairly flat, but it requires a talented machinist to do it, and that’s why there is such a huge backlog at these shops.
Candidly, our level of initial flatness blows any shop away. See for yourself in the attached picture. You’ll see sharpie marks right on the case that Harman marked after we cut this one. The notations are in tenths. For you non machinists, here are the way these are measured:
– The average human hair measures .004″
– One thousandth of an inch is .001″
– we are measuring in tenths, which is .0001″
So when Harman writes +4 in sharpie, what he is saying is .0004″ which is one tenth the thickness of a human hair! Oh, and that is our worst measurement. Most of them are zero, meaning we can’t measure any further.