(07-04-2018, 12:32 AM)KnifeGrinders Wrote: ... A prerequisite for calibration is that the laser pointer is at the same distance to the knife edge ...
Jan's diagram illustrates the geometry at work. Visualize sliding the laser left and right, and you'll see alpha is independent of the distance between the laser pointer and the knife edge:
Measuring alpha requires a fixed distance in the plane of measurement between the knife edge and the measurement scale. The DILAGON achieves this via the 2-step procedure of measuring the offset in the plane of measurement between the knife tip and the knife edge, then positioning the tip back from the origin of the protractor by the measured offset.
While this procedure establishes the correct distance between the knife edge and the measurement scale of the DILAGON, it does not ensure the edge is optimally aligned in the laser beam. Alignment is done by freehand adjustment of the knife's roll and yaw, neither of which should have a significant effect on the accuracy of the measurement.