Calendar readout control levers, begin digital year indicator - April 2015
These arbors are for
the various release functions to set the dial work.
The three brass components are the sequencing
cams that control the release of
day, date (uses the same cam) and month and year. They all mount on the
calendar input arbor which revolves
daily for each
operation. Similar to the four legged cam on the strike
created four years ago in
These are the rocking levers which turn the forward or reverse motion of the
sequence cams shown above, into a smooth forward or reverse direction for
the connecting levers that will control each of
bird analogue detents.
There are a total of six, for the forward and reverse functions for the day
month and leap year. These rocking levers working together with the cams,
within the perpetual module, bird analogue detents along with the matching crenulated
output wheels will act as computational ‘logic gates’, often referred to in
computer design as AND,
and NOT gates. These mean that when a certain input is registered, the
output will be the result of the programmed logic gate and will follow a
certain pattern. This computational logic is the result of the surprise
pieces controlled by the various cams within the perpetual module.
Logic gate truth table. Now let's see how these gates apply to our
mechanical perpetual calendar calculator.
In the Gregorian calendar three criteria must be taken into account to
leap years: First, the year is
evenly divisible by 4; second, if the year can be evenly divided by 100, it
is NOT a leap
year, OR the year is also evenly divisible by 400; the
third order. This means that 2000 AND2400 are leap years, while 1800, 1900, 2100, 2200, and 2500
are NOT leap years. When these criteria are accounted for
the calculator is permanently perpetual; it is a third-order perpetual
A basic first-order perpetual calendar accounts for the quadrennial leap
years. That is, a four year perpetual calendar. The next complication is the
100 year calendar where at the end of that 100 year period the leap year is
skipped. To keep the calendar in synch that skipped leap year must be
continued for the next three 100 year intervals. That is for the next 300
years, every 100 years a leap year is skipped. The 400 year perpetual
calendar then allows the leap year to be re-inserted once every 400 years;
making it a perpetual calculator.
Of course it goes without saying that the
calendar properly accounts for the regular sequence of the months ending in
30 or 31 days.
Illustrated above is the
method used by Mr. Martin Burgess for the calendar dial's crenulated wheels. In
essence they are freewheeling, but are so light that they will run along
with the underlying toothed drive wheel since they are mounted upon those
drive wheel arbors through the use of a cannon arbor not unlike the
arrangement used in a conventional motion works for the hour and minute
hands, but instead of these being isolated from each other they are allowed
to contact. So when the drive wheel turns the crenulated wheel upon which
the dial hands are mounted will turn with it. This is because there is
contact between the inner arbor of the drive wheel and the cannon tube that
surrounds that inner arbor. Buchanan describes the process as follows: "The
first time I examined Martin Burgess clock, the one installed at Schröder
in London, which used the same principle, it took some time to realise just
how simple the principle was, and there were two of us and we had it in our
hands! I think you will also understand the need for poising and that I
cannot use a castellated wheel to perform any work although we can obtain
information off it. It also makes hand setting easy as all we do is lift the
latch and move the hand."That castellated wheel is beautifully
illustrated in the February
We now can see why it was so important that the entire perpetual module be
Here we are employing another fairly unique design feature to this machine.
These videos demonstrate the Martin Burgess clutch used to drive the
crenulated output wheels which are connected to the readout hands.
Buchanan has made a temporary front plate for the calendar multi dial
cluster from clear plastic so as to give the viewer a better understanding
of the fabrication process.
This photo shows the rough blank for the lever that will read the crenulated
daily index wheel of the perpetual module.
This photo shows that blank refined into its final, curvaceous shape which
follows the rid line just to the left. The red arrows highlight the
decorative organic plant spurs that are used throughout this project.
sinuous trip linkages which will control the bird analogue detents begin to
take shape. The circled area shows a flat on one of the levers that connects
with a pin on the
crenulated wheel. This provides for the once monthly trip.
See how this lever becomes more refined from left to right, red arrow.
Next the collet used to attach that lever to the one below it and rotate
both around a common pivot point.
The lever before and after decorative shaping.
The videos below show demonstrations of the calendar drive.
The first video demonstrates a 28 day February, the second a 31 day month.
This video demonstrates a 30 day month.
These photos show the toggle mechanism which replaced the solid, immovable
wire as illustrated
towards the end of
the February instalment,
which was used to read the various cams and crenulated ring on the
It solves the lag time for the change of the date as it relates to the rest
of the calendar dials when the calendar is run in reverse.
Here we see a demonstration of the calendar being run in reverse for a
normal 28 day February.
Can we possibly cram in any more parts? Yes we can, and we will!
Quadruple frame calendar module
The complex calendar mechanism is housed between the quadruple frame assembly yet it is completely removable
as a unit from the rest of the movement. From left to right the frames
contain: forward remontoire, reverse remontoire, calendar works. Below the
horizontal pillar is the overdrive safety clutch built last month.
Buchanan now begins the fabrication of the
The first step in trying to create a mechanical digital counter is to
see how these function. It is not the sort of mechanism one normally
encounters in a clock. The first photo shows a couple of modern inexpensive
digital counters which were taken to pieces. In the next photo one can see a
digital counter in the background on a clock by the custom clockmaker
La Vallée of Como, Italy.
readouts have ten flat surfaces, in other words the ring has ten facets one
for each digit. I found this to be a nice innovation over the conventional
cylinder readout and when done properly is far more legible.
One of the key things learned from the forensic observation of the
commercial digital counters is the type of tooth profiles used in those
devices. Conventional clockwork uses cycloid tooth profiles for the wheels
and pinions. That
design, however, has too much lash to be useful in this mechanism. Here one
needs to have each digit disc align as accurately as possible to its
neighbor so that all of the four digits for the year are perfectly in
alignment as possible. This required Buchanan to make a custom tooth design
to achieve this goal of minimal lash yet having a smooth drive between the
digital discs. The type of tooth profile for the discs was very close to a
perfect circle. So a drive pinion had to be made to mesh properly with this
type of wheel tooth profile.
Here we see
the making of the ‘carry’ pins. These are located on the opposite side
of each digit disc and after
a complete revolution of the disc will advance the adjacent decimal wheel to
the left by one digit, thereby carrying the calculation forward. This allows
the additive calculation to continue through to the next decimal counter and
so on. In
example we have four decimal wheels so the first, rightmost
wheel would have to rotate ten times to advance its neighbour by one digit,
and turn 10,000 time to completely turn over the entire set of four decimal
Here is how
how a new custom tooth profile fly cutter is made. The first photo is a 50x paper pattern of the
pinion tooth gap. The second photo shows the optical profile grinding
machine that will convert this to the actual size needed to grind the fly
cutter needed to make the pinions. Buchanan describes the process: "
The gear to be copied is placed on the work table. Above it is a microscope
attached to a 50:1 pantograph arm (red
at the end of the arm is a pencil. By manipulating the arm one guides the
cross hairs of the microscope along the profile of the gap in the gear tooth
and a 50 times over size copy,
is drawn on the drawing table. One then replaces the sample gear with the
cutter blank and then by plotting along the line, or cut out, on the paper,
one manually manipulates the vertically oscillating grinding wheel to grind
away the tool until the cutting edge is up to the cross hairs of the
Then the microscope is moved along the profile a little further and the next
portion of the tool is ground back. In theory one produces many small steps
along the profile but the edge of the stone has a radius and the steps blend
somewhat. Some practise is needed and good hand eye coordination helps a
lot. The line of oscillation of the grinding wheel can be adjusted to give
the correct cutting angles. Once cut the 8 tooth wheels need half a tooth
removed the work correctly."
The custom fly cutter is shown next to one of the pinions produced from
it. The cutter was made to fabricate only three drive pinions.
The last line Buchanan writes above about a half tooth being removed is
shown in these two photos. Half of the width is removed from every other
tooth. This is necessary since the eight teeth of the pinion on the unaltered side are in
constant mesh with the ten pins on the decimal wheel to the pinion’s left.
However on the opposite side the pinion must mesh with the paired ‘carry’
pins that are on the neighbouring decimal wheel to the right. The alternate
milled areas are required because the paired carry pins require twice the
area than do the single ten decimal pins. If one tried to drive the pinion
without its neighbouring tooth milled down, it would immediately jam.
the ten facets are milled onto each decimal wheel.
Buchanan has now
fretted out each of the decimal wheels. Once more I must point out that he
has taken the ‘high road’ in his quest for the maximum quality and
of what I believe sets his work apart from all others, his skillful fretting
out of every conceivable part. These wheels are close-mounted to each other
and it would be difficult to see if the outer, let alone the two interior
wheels were spoked; not to mention that these are only about one half inch,
(1.3 cm) in diameter.
Year digital counter demo showing a minimal amount of lash between the
decimal wheels; allowing for good alignment, yet a smooth meshing between