For the prototype case, we originally used an end mill to create the cylinder spigot holes. For those not brushed up on their cylinder spigot tech, here is the quick primer:
Porsche cylinder spigot holes hold the cylinders in a pretty loose slip fit. If you’ve ever built a Porsche engine (many of you have), you will note the cylinders can be slipped into the case and removed by hand. There is acres of clearance, and it’s done that way on purpose.
Using an end mill to make the spigot hole is a simple procedure – the end mill rotates in a circular shape that is controlled by the 5 axis mill’s accuracy. The hole is only as round as the machine is accurate, so we of course tested this. Using our brand new Haas UMC-1000 5 axis mill, we got circles that were pretty darned round, I’d say with about 8/10ths accuracy (.0008″). This was pretty round, but I was not impressed with the surface finish.
Wait – no one sees the insides of the cylinder spigots. Also, I just finished saying the clearance isn’t super critical. Both true, but hey, we are making jewelry here so…..
I decided to upgrade our hole making ability by an order of magnitude – we are now using a D’Andrea boring head. Are you a boring head aficionado? I am :-), and D’Andrea (pronounced dan-DRAY-uh) is an Italian company that makes the Bugatti Chiron of the boring head world. Their equipment is top notch, but you pay for it. Our boring head costs over $2000 and mills perfectly round holes to .0002″. It simply does not get more accurate than this, and we are shooting for the moon as far as accuracy goes.
All in furtherance of the most accurate case possible!