As a public service, I’m posting in these pictures how you calculate and drill bolt circles.
The calculations are from a 1949 Sperry Gyroscope Company drawing, but the same material and table data is in your Machinery’s Handbook… This data may have been used to design the secret Norden Bombsight.
PROCEDURE:
1) Calculate the offsets.
2) Mount & Center the part with your dial indicator.
3) The top hole is at half the diameter of the bolt circle, at .000 along the bed.
4) Machine away!
Rocky
PS - This data is good for all bolt circles - up to wheels with 12 lug bolts!
