Ron Walters's 4-digit counter
The cardboard box in the photo is the same size as the original full-size 3-digit counter. Reducing the dimensions 50% would produce a 3-digit counter 1/8 of the original volume. With the 4th digit added, my version is around 28% larger than that or roughly 1/6 the original size.
The paper template in the photo is for the original full-size plans is shown for size comparison. My gears and carry notch discs are made from 1/8" tempered hardboard. I made my carry gears in three parts, two (2) 1/8" thick 8-tooth gears and one (1) 1/8" thick 4-tooth skip-tooth gear. The carry notch discs and the carry gears were glued together with Titebond Glue.
The carry gear and main rotor shafts are both 1/8" piano wire. The center points for all holes were accurately located with an optical center finder (Lee Valley Tools). The axle shaft center holes were first drilled with a 1/8" brad point bit and then re-drilled with a No.30 (0.128) bit, which provided sufficient clearance for the digit wheels to turn freely.
The digit wheels were spray painted with flat white paint. The digits were rubbed onto the wheels using Matthias's process and then drawn using a Sharpie ink marker - ultra fine point. As an additional point of reference, each number should be centered on every other notch of the Advance Gear.
The Geneva Drive or carry notch is centered on the "7" on the Unit's, Ten's and Hundred's digit wheels (ref yellow line). The carry notch is also aligned with a notch on the Advance Gear.
The plywood top fit perfectly. Other than modifying the top, bottom and back due to the wider 4-digit counter, nothing was measured. I just cut out the pieces using the templates, which I printed at half-scale using the BigPrint Program. I used a scroll saw and then a scroll saw file to just sand away the template lines on the wheels, carry notch discs and ratchet advance parts. I was quite impressed with how accurately all the half-sized parts fit together. I had to do zero fine-tuning of the gears or carry notches.
The ratchet advance parts are made from 1/8" 6-ply aircraft grade plywood. The grain of the two center plies is aligned to essentially make this 5-ply plywood. Note: Plywood is normally expected to have an odd number of plies so the sheet remains balanced against environmental changes (adds stability to prevent warping).
I wanted the Advance Lever to return to center when incrementing. I used a straight piece of 0.032 piano wire for a return spring pushing against a 1/8" dowel I added to the advance lever. I did not provide a return spring for decrement, as I did not need one. If I wanted a decrement return spring, I would experiment with the location of a second 0.032 piano wire as suggested by the red line.
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