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Finish calendar dial drive wheels. Begin the reversible, perpetual calendar calculator module - January 2015

The crossing out of the calendar dial drive wheels is now complete. The smallest wheel, Buchanan tells me, is as small as one can cut on the jeweler’s saw which he has used to cut all of the flat stock on the clock so far. Smaller wheels than this will have to be spoked out through a spark erosion (EDM) process.


These photos show the fabrication of the various pinions for the calendar dial drive wheels. Note the matchstick for comparison in the fourth photo.


The solid disks have small ‘V’ shaped groves which will act as does a star wheel in conventional calendar work. These serve to make the dial hands jump from one date to the next in discrete steps. This design is made necessary because all of the dial drives are directly geared together and not actuated by a pin engaging a conventional star wheel. The last photo shows the tubes that will carry these count wheels.

The count wheels are now spoked. When I first saw them I was pleasantly surprised in the way Buchanan followed the contours of each ‘V’ groove rather than making the interior of the rim a smooth circle. Once again his elegance shows through in the extra efforts made. The third photo shows day detent wheel mounted to its cannon arbor.


The first photo shows the detent wheel with its cannon pinion mounted onto the arbor of the mating drive wheel.

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Buchanan begins to make the reversible, third-order perpetual calendar module.

The second photo shows a wheel pointed out by the pen that is fixed to the frame in the calendar mockup, it will act as the ‘sun’ in a sun and planet epicyclical gear system. Next Buchanan points to the position that this sun gear will occupy. There will have to be a bridge built just above this drive wheel to fasten the gear to. The last two photos show a preliminary view of how the calendar drive wheels will look behind the dial cluster.


This is the sun gear and it’s safe to say that this one will be the first wheel in the one hundred or so made to date that will not be spoked out!


 The sun and planet gearing is shown in these photos.


Next the date detent wheel is shown next to the same wheel in the mockup. That squared plastic tooth wheel is three times the size of the actual one in brass. The last photo is an overview. The top gear covering the date detent disk is covering three layers of gears below. The largest is 90 teeth and just under 5/8 inch, (1.5 cm) and the smallest is 35 teeth and inch, (0.5 cm); module 0.18.



Here Buchanan makes what may be the smallest gear in this project at only 1/8”, (3 mm). The first two photos show the setup on the mill. Next a close up of the cutter and pinion before cutting. Next a few photos to show the scale of that part, especially nested between the teeth of the largest wheel in this project, the main going barrel. Last a 20x magnification of the wheel teeth during the depthing operation.

Here a small bridge, similar in design to that found on a tourbillon is fabricated. The purpose of this is to hold the small attached gear as seen in the first two photos. The bridge is in place in the third photo and that small gear is held in place, facing upward and floating just above the large wheel below.



Here the tiny gear gets installed and is shown with its chaton. The next photo shows a wheel that is mounted to the same arbor as that gear from below. Third photo shows the wheel from above mating to the pinion. The last photo shows the completed assembly with the gear (red arrow) and the other fixed gear that was described in the prior installment, (yellow circle).

The first two cams, the four and twenty year correction cams, are now being fitted with their associated drive gear.


Buchanan had to make five tries to get this nine toothed pinion. Adjusting the cutter to the center of the pinion blank is critical as an error of only 1000th of an inch spoils the part. The module for this part is 0.15, the diameter is 0.63 thousands of an inch or 1.6 mm. Next are the gears for the 20:1 leap year cam. Tooth counts are 33:66 and 9:90.

We have now descended to the smallest scale that will be encountered in this project. The three tiny screws are used to attach the wheel in the next photo to its collet. At this size it is no longer possible to spoke a wheel using a conventional jeweler’s saw. The wheel thickness is less than the space between even the finest teeth in a saw blade. These are now at the scale of pocket watch work. The conventional way watch wheels are spoked is either through stamping using tool and die methods or through the use of extremely accurate computer controlled micro-milling machines. These methods are only practical in a full scale manufactory producing parts in volume. Here we are making a one-off part. So Buchanan turns to EDM technology.

The third photo shows how the wheels are cut out using an EDM machine. The wheel blank is submerged in an oil bath while a copper electrode, above, is lowered to contact that wheel. The electricity then vaporizes the brass blank where the electrode is in contact. The design is completed through repeated contact until the desired spoke pattern is formed. The fourth photo shows a copper blank cut to the spoke profile and it is the positive die that electrically erodes the brass wheel blank to produce the spoke pattern. Next a set of copper dies for the various wheels in the perpetual calendar module and finally some of the completed wheels. This method is slow, but once set up requires little attention. The copper dies are made from relatively soft metal and the pattern easily machined. We have used the EDM process before to make some special conical holes in the main frame pillars but this is the first time it was used to make individual parts. Much later in the project we will use this method to create a fine matte decorative finish in some of the frame pillar parts.

A small cock is now fabricated. Note the tweezers for comparison. Even at this scale two locating pins are used as is best practice for clock and watch making. The third photo shows the pivot being drilled with a very tiny drill.

The rough blank of the cock is now in place.


Filing buttons are used to give the decorative contours needed to bring about the final contours of the cock. And yes, we are jewelling the pivot. Every pivot of the estimated 1000 to be completed is either jeweled or equipped with roller bearings with about two-thirds being jeweled.


Notice the beautifully machined pillar that supports a steel collar. It is only a few millimeter high. The next photo shows how small this part is as well as the fact that the entire perpetual calendar module is on the order of a conventional pocket watch. The attention to detail is penultimate.

Here we have the Geneva cam which will drive the 100 year cam in 20 year increments, hence the five cam lobes.

The various parts to the 100 year cam are shown. Note the tiny square holes in the center photo.


Here is the set up the fabrication of the small square holes and square arbors. The second photo shows one of the very small square posts at 20x magnification.

This photo shows how deep the calculator will be and the reason why Buchanan had to have a the clearance which would otherwise seem unnecessary for the rest of the calendar drive wheels behind the dial cluster.

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