The middle case is at the heart of the engine. It sits between the front and rear cases. It has two cavities on either side that create the internal space in which the crank cheeks rotate.
The picture above shows the completed middle case front cavity. The center hole which holds a bronze bearing for the crankshaft is bored through, and the lip at the edge of the case is cut in the same setup to make it concentric with the bearing hole.
Back to the mill to hog out the rear cavity before finishing it on the lathe. I use a coaxial indicator to pick up the center of the bored hole.
Living up to the web sites name, hogging out with a 1 inch end mill creates lots of swarf. Both the main pocket and step being cut are created using D2nc. You can see in the image the tool is ramped into the material using D2nc’s ramping feature.
The middle case is returned to the lathe and the rear cavity is completed to finished dimensions. The recess in the center of the case will house the two oil pumps, pressure and scavenge, which are contained in the engine. Once again the lip which mates to the rear case is machined concentric to the bearing hole.