I fastened a post to the top of the rotary table as the means of finding the crankcase mandel's centerline once the case was installed. The photos show where an edgefinder was used. The DRO made this very easy since attention need not be paid to backlash in the machine's leadscrews.
The photo to the upper right shows the edgefinder being used to locate the case's radial position. Initially the crankcase was going to face the other direction so the through bolts were drilled to allow that. With the change in direction all of the case angles were 25 degrees off. Some simple math and a newly printed sheet of case angles were made and it was back to business. Although I really only needed to drill one locating hole I did it all around the case. Only one dowel is used for locating so there is no chance of having differing results.
The picture to the right shows the edgefinder doing it's thing. The edgefinder is accurate to .0002"
Initially I thought that drilling some 1/2" holes would allow me to use a depth mike accurately enough for the case to centerline distance. After seeing that this assumption was wrong I decided that rough milling the case flats then boring the cylinder bores would allow a better view and allow for cleaning of the measuring surfaces. The hole saw left a hole about 3.5" in diameter; well under the 3.812" that the final bore would be. Chips from milling made the shop look like a winter wonderland. Since I was always taking light cuts the rough milling of the case flats took about seven hours.
The case started out as an 11" round of 6061 aluminum. The distance from case flat to centerline is five inches exactly. Can you imagine how much longer it would have taken if I started out with a larger round of aluminum?
