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Complete the reversible, perpetual 400 year calendar calculator module - February 2015

Shown here is the four hundred year cam assembly. The four lobed Geneva cam will rotate once in 400 years in four 100 year increments.


The first photo shows a brass blank with holes being drilled for wheel pivots and fastening points. The blank has been made to copy the diameter of the rest of the perpetual calendar calculator so as to better ascertain the correct proportions for the frame that will be cut from this. Next the decorative upper frame is cut from that blank.


 Next are two photos showing the layering of components both below and above the frame.

Now the main construction of the date mechanism of the calculator is finished. Note how small this is. Next the module is shown in the context of the rest of the calendar mechanism.


These photos show how the perpetual calendar module will look with the context of the rest of the calendar work. It is located behind the date dial at the apex of the calendar dial cluster. One can readily see why there is so much space between the dial cluster and the rear plate. That space is needed for the perpetual calendar module. The solid disk will later be fretted out.


The three ‘surprise pieces’ are shown in the first photo. These were first described in the October 2014 section of this project. The term ‘surprise piece’ is a phrase first used in the 18th century in connection with pocket watches that performed complex repeat functions in their strike work. Quarter and minute repeat functions required separate, movable steps to add or subtract from the profile of the snail work steps used to count the strokes of the strike hammer. What these parts do is to add or subtract the number of detents that are present to read the output for the date. The top piece is controlled by three cams, each rotating once in 20, 100 and 400 years to introduce or remove the 29th day in February that are exceptions to the regular four year leap year cycle. The next two are controlled by the normal four year leap cycle as well as the cam indicating the months having 30 and 31 days. Notice that we still continue our ‘bird motif’ even in these very small parts. The extended beaks on the top and bottom pieces are not necessary to their function. The next photo shows these pieces in place within the module.


The surprise pieces are now assembled. Even these small spacers have some decorative turning. The perpetual module contains four independently rotating disk-shaped platforms numbered 1 through 4 as shown in the fourth photo. All platforms contain some combination of wheels and cams. Each one will, as the finishing progresses, be poised so as to minimize the amount of energy needed to rotate them. The fifth photo shows the overall module cage on two parallel knife edges used during the poising procedure. If this precaution were not taken, then conceivably, at some point in time all four rotating platforms could align where each has its greatest imbalance resulting in a possible stoppage.

Here we have another example of Buchanan's tour d’ force of his skeletonising techniques. The solid, crenulated date disk seen in the prior segment is now fully fretted out. Any other conventional maker would have simply left a solid inner rim, thus saving a huge amount of effort. But here he follows the crenulations exactly to produce a magnificent and delicate undulating rim design no larger than a silver Dollar coin, 1.5 inches, (3.5 cm) and is as thick as a thin piece of cardboard. Also shown is the 30 or 31 day cam for the month; the first of several oddly shaped cams.


The first photo shows a front view of the calculator and attached is what looks like a chapter ring, red arrow. This is the base to which, in fact, a tiny chapter ring will be fitted with the individual months of the year, second photo. The engraving will later be cut into the final ring shape and silvered with the lettering filled with dial wax.

One can see how incredibly crisp the engraving is at this small scale. Buchanan says that he sharpens his engraving tools with diamond lap cutters. Then to be sure the spinning engraving tool is set perfectly dead center in the lathe chuck he lets the tip touch nail of his finger to feel for any shake. He readjusts the tool in the chuck until all vibration is eliminated. This allows for maximum accuracy for the engraving cut, as well as several small holes in his fingernails.


Next is some of the hand filing used to shape the cams. The month chapter ring is then installed. It seems a pity that the foot of the drive wheel cock has to be mounted over the month of January, red arrow, completely obscuring it. Later this part of the ring will be completely cut away.


Here we see Buchanan using a piece of clay to poise the one year cam along with the month chapter ring. The perpetual calendar module has four separate rotating assemblies and each must be individually poised. This prevents any problems that could arise should all four assemblies, if unbalanced align into a quadruple un-poised position. A situation that could occur every 400 or so years. Next the assembly is shown nearly poised.


The twenty year cam is cut out on the piercing saw. The 400 hundred year cam assembly is seen just to the right. Next the twenty year cam is installed in the second photo just above the month chapter ring.

Next the module is reinserted into the calendar subassembly and in the second photo one can see the need for the deep clearance between the dial and rear plates. Next the 100 year cam is shaped by hand filing.


The twenty year chapter ring is installed on the twenty year cam along with the 100 year cam mounted in the 10 o’clock position. Note the fairly complex contours of this part. Next to it is the 400 year cam assembly.

The two main subcomponents of the perpetual module.

 This photo shows how petit this whole calculator really is.

Here are the main components of the reversible 400 year perpetual calendar calculator. The total comes in at a bit over 102 parts. The main components are as follows:

1. Daily index wheel, this advances daily and is where the drive to the calculator begins

2. One year cam, controls the duration of February in non leap years

3. Ten year cam

4. Twenty year cam

5. One hundred year cam

6. Four hundred year cam

7. Twenty year chapter ring

8. Month chapter ring

9. Calculator frame assembly, partial

A. Four hundred year drive assembly


The S1 through S4 surprise pieces described below operate in the open area of the rim at the 3 o’clock position on part #1, the daily index wheel.

S1, S2. Dual surprise pieces that are controlled by both the 100 and 400 year cams

S3. Surprise piece for introduction of extra day in February in normal four year leap cycle

S4. Surprise piece for the introduction of the 31st day in the appropriate months, excluding February

The remaining parts are ancillary drive wheels, Geneva drives, fasteners and support parts.

These photos give a comparison in both weight and size of the calculator in relation to a wrist watch. In the first photo the wrist watch movement comes in at 36.1 grams with the calculator, second photo, weighing in at 29.7 grams, 1.047 ounces.



The completed calculator. It looks a bit reminiscent of a skeletonized tourbillon escapement model.


The first photo shows the calendar parts to date and those parts including the perpetual calendar module mounted behind the calendar dial cluster. That cluster is currently still a wooden mockup.

Now we turn back to the rest of the calendar work. The first photo shows the hand filing of the detents which have again been shaped into the characteristic bird analogue used throughout this project. The five detents will be used to read the output of both the calculator and balance of the dials are shown in the next three photos.

Those detents are now in place (red arrows).


The first photo illustrates a set of paired detents used to read the data from the calendar module. There is actually only one detent, the one in the background which reads the crenellated daily index wheel. It is connected through a wire to another nearly identical looking piece in the foreground which only serves to secure the other end of that wire. Both parts are fixed to and pivot upon their arbor on the left. The wire is necessary as there are three separate cams positioned across the width of this module that will actuate the rear detent through contact with that wire at various times throughout the calculator’s 400 year cycle to either engage the crenulated wheel or keep the wire raised so one or more teeth on this cam are skipped. The last photo shows one of the bird-analogue detents located into the leap year wheel groove.

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