Drilled the hole pattern today. Required hole pattern diameter of 111.125mm (4 3/8"), 6 holes with 60° split, were drilled on the dividing table of the deckel mill. I used a 27 hole dividing disc which made me turn the lever 6 times plus 18 hole distances per 60°. I drilled the holes to 15.7mm and reamed them afterwards to about 15.85 to make them fit the lugs on the flange.
Centering the spindle was the big issue. If you start off with a minor offset already, the hole pattern wont match the one on the engine!! I started first with an edge finder to bring it as close as possible to an absolute "0" G55. Afterwards I crosschecked and improved the absolute "0" with a special caliper mounted in the spindle. It turned out to be within 0.005mm 360° around the the center hole checked.
From the absolute 0 position, I moved the "Y" axis to 55.56mm and crosschecked the 6 hundrets with an other caliper against the mill indications.
I predrilled all 6 holes then with a 10mm milling cutter and on the second turn with the 15.7mm.
At the very end and after the fitting, I drilled 6 10mm holes to take some weight off!Those are in a 30° angle to the 6 main holes.
