Strike and repeat control assemblies, complete initiators - April 2011
This month we continue with the fabrication of the
strike and repeat control initiators.
The above photos show the fabrication of an additional drop down frame which
will house the components of the strike and repeat initiator systems. Note
that we keep our design consistent with that used for the time train
remontoire fly fans.
The components consisting of the initiator wheels and their fly fan are
preliminarily tested between the pillars.
The ratchet wheels are fitted to the initiator fly fans.
The mating ratchet pawl springs are fitted. We keep our
design consistent in that we use oversized curvilinear springs for the
ratchet pawls. It is the same design used in the remontoire fly fans as well as the
main winding barrels. These springs are not only decorative in this form,
but also, due to their geometry, offer a more consistent and gentle force on
the ratchet pawl. Notice in the second photo we keep our bird's head design
for the pawl. This part will later be blued. Also one can see a chaton with
the red plastic 'jewel cap' removed revealing a ball bearing assembly.
Buchanan now begins the fabrication of a mount that will hold one of the
leaf springs which will 'load' the initiator wheels. The first two
photos show the part still attached to the rough block. Next the part is then sliced off with the slitting saw.
The part is now mounted to its position on the drop down frame along with
its spring. Note the two red jewel caps which cover similar ball bearing
pivots shown four photos back. The next two photos show the overview of the assembly.
A close up of the assembly.
Now begins fabrication of the quarter strike cam detent. This part is driven
by the time train and will trip the quarter striking under normal operating
conditions. It will trigger one of the two initiator wheels that will begin
the proper sequence needed to drop the quarter rack into place. Note that
Buchanan cuts this complex piece
in one pass out of the
solid blank; just as was done on the
pendulum balance anti friction wheel
cages. A steel rim is attached around the
jeweled piece. In this way we obtain a more finished look.
The first photo shows the initial mount for the tellurium in the
foreground with the initiator wheels in the background. Next the assembly
mounted within the movement frames. Third photo shows the first,
conventionally designed sector gear that will both load a leaf spring and in
turn use the energy from that spring to spin the initiator wheel. The last
photo shows the quarter strike cam in place.
Now begins the fabrication of the second sector gear which is involved
with the repeat function. The initiator wheel
in connection with this gear needs to turn in the opposite direction.
We have a pair of wheels and drive sector gears that are related closely
both physically and operationally, but need to be power the initiator wheels
in opposite directions. Here is another example where the design and
engineering expertise of the Buchanan firm shines. An obvious solution would
be to insert a small gear between another conventional, externally toothed
sector gear and the initiator wheel in order to obtain the needed counter
rotation. We chose another way. Throughout this project we ask ourselves
"How can we make this part in such way as to fascinate and engage the
viewer?" In this way we create not just a complicated and interesting
mechanism, but a coherent piece of horological art. Our solution is both
elegant and simple in theory, but a bit more difficult in execution. A
scenario encountered many times. The second sector will have its teeth cut
internally on the inner rim rather than on the outside rim as was
done on the first sector gear.
The first photo shows the brass blank with the sector gear's internal
space cut out. The space within the sector is too small for Buchanan to
employ the same setup that was used to cut the internal teeth of the two
time train remontoire fly fans. See the chapter for
April 2008, as
well as the video
showing that procedure. Since the cutter cannot be mounted to a proper
drive, Buchanan has clamped the cutter to a small tube vise, second photo.
The third photo shows how this setup fits within the confined space of the
sector's cutout. The vise is then mounted to a reciprocating head on the
Bridgeport machine, last photo. Instead of the cutter spinning to create the
sector gear teeth, a single tooth of the cutter is reciprocated to do the
These two photos show the tooth cutting progress, note the cutting wheel
at the top of the second photo.
The rough blank is fitted to the initiator assembly and when satisfactory
the internal toothed sector gear is fretted out, but is not yet
The two sector gears are now shown fitted side by side with their mating
wheels. A nice presentation.
The initiator springs, once fabricated must be heat treated to bring
about the proper temper. These springs need to be quite strong (stiff) to do
their job. The springs are packed into a copper tube along with charcoal.
The tube helps to distribute the heat evenly and the charcoal keeps surface
scaling of the metal to a minimum. The package is heated at
8100 Celsius (14900
F) for one hour. Afterward the tube is quenched in a can of oil (see video
below). These will later be polished and blued. The quarter strike spring is
Buchanan now fits the rough outline of what will be the lever that will
be used to depress the internally toothed sector gear. This is the repeat
initiation function. The last photo shows this lever in place just behind
the tellurium dial. (See video below to view this and the quarter strike
The externally toothed sector gear is connected to the strike initiator
wheel and is triggered by the quarter strike cam. This part is now fitted
with a spring-loaded safety lever, first two photos. This is needed in the
event that the quarter strike cam in turned backward as would be the case if
the hands on the clock were pushed backward. The third photo shows the cam
depressing the lever in the normal operation; the cam turning
counterclockwise. The last photo shows the cam approaching in the opposite
direction, clockwise. The lever is harmlessly lifted out of the way and when
the cam's wheel passes, snaps back to its proper position. This is another
example of our trying to make this clock as user-friendly as possible. On
most clocks, particularly those with strike features, one would never turn
the hands backwards, but we design for this event.
Buchanan now makes some of the flat jewelling needed in the strike lever
For those who cannot use the built-in viewer I have added the YouTube