Andrew James contributed: >In any >case I could see clear benefits in drilling the holes and using pins as >I surmise even for a "one-off" because of the certainty of the lines >converging accurately to the same point for minimum effort in >positioning a straight edge. I have used a corner of something clamped >to the plate for the same purpose of locating a long ruler when drilling >was not a preferred option.
I'm pretty sure these conclusions are correct and in that connection have often asked myself how I would have performed the task of dial division before the advent of dividing machines. My own solution would have been a 'dividing room' with a central work surface to which the blank would be attached. Surrounding this, perhaps at a radius of several feet to increase accuracy, I would have an narrow annular strip at the same level as the blank. This might be of wood with a brass facing with locating peg holes at e.g. 10° intervals carefully located by trial-and-error stepping with dividers. A movable 10° sector with locating pegs, further divided into degrees and perhaps minutes, could then be placed wherever the current hourline was being drawn removing the need for a full circular calibration. A long straightedge between the scale and central pin at the dial origin would then be in place to assist engraving or marking through resist for etching with sufficient accuracy for a high quality dial. Two men working together, one at the outer scale and the other doing the marking, could then calibrate a dial very quickly. No doubt I'm entirely wrong and there was a much simpler way of doing it but these are the thoughts which occupy my idle moments. Nowadays of course it is just an angle in a dialogue box and a keystroke. Tony Moss -
