Finding bottom edge of a disk

[compact8]

When using a pin to locate an edge we would spin the pin in the chuck against a dti and mark the high spot with a sharpie. This confirmed that the two concentric spots on the pin were at +/-90 degrees to the mark. Then used either of the two concentric points by having the mark 90 degrees from the face.

Another way is to close the gap at a randomly chosen angular position of the spindle. zero the DRO, then rotate the chuck by 180 deg, close the gap again and half the new DRO reading by using the 1/2 function. At this point the center of rotation of the spindle from the edge is pin radius + DRO reading. I use this method for my cheap electronic edge finder which has some significant runout.

 

[mws]

Isn't the bottom of the disc coplanar with the top of the 123 blocks?

That's what I thought!? He meant lower edge in X not Z. LOL!