Chuck Mandrel for a small 5” 4-jaw Chuck

[mklotz]

I'm trying to figure out how to do bolt circles especially when there is no center point to go by, as in the brake rotors on my trike.

If the center of the workpiece has a largish hole, find the center by sweeping the hole with a DTI. Then you can locate the bolt holes by coordinates. You can use the program BOLTCIRC from my page to calculate the coordinates relative to the center or calculate them yourself using the following equations...

n = number of holes
r = RADIUS (half the diameter) of the bolt circle
a = 360 / n = angle between adjacent holes

Calculate x,y coordinates, measured from the center of the work, as follows for k = 0,1,2, ... up to k = n-1

x = r * cos (k * a)
y = r * sin (k * a)