Complete strike and repeat control assemblies, quarter and hour racks - July 2011
This month Buchanan continues with the fabrication of the strike
train control systems and now proceed with the fabrication of the quarter
and hour strike racks. These are made of both brass, for the tail portions -
that part which contacts both the associated snail cam as well as meshing
with the pinion of the rack let down fly, and steel for the saw toothed rack
itself. The steel portion will be later polished and blued.
These photos show the initial blank for the hour strike tail
in paper. Notice how the paper is rotated to check for full movement between
the first and second photos.
Next that paper blank is positioned on the brass blank. The
outline is next scribed. The next photo shows the mill cutting the teeth
into the tail. These teeth will mesh with the fly let down pinion.
Next the quarter rack tail paper blank is tested for
clearance within the movement. As with the hour paper blank, it is then transferred to
brass stock and this is now mounted to the mill. This part has internally
cut teeth and these are cut in the same fashion as the internally cut teeth
for the repeat function
Notice the support given near the area where the
reciprocating blade cuts the internally toothed tail piece. The next photo
shows a close up of this process.
Next the brass hour strike tail is fabricated as well as the
actual rack from steel, first two photos. The next two show the rough hour
and strike racks in place on the movement being checked for fit.
In the left column of photos are the rough quarter and hour
rack assemblies. To the right are the design drawings depicting the finished
Both the t
brass and steel portions of the rack outlines are cut with a hand fret saw. All
of the steel components are cut with an old fashioned fretting saw, all by
hand with lots of elbow grease. Once again
contributing to the hand-built nature of this project.
e photo above is the quarter strike rack. The
actual teeth are cut by machine to retain meshing accuracy. The part is then
tested for functionality within the movement below.
Note how the sector gear is highly raked to compliment the general curvature
of that part of the component. It almost disappears within the curve. Some finish filing has
been done to enhance the part.
The lower two photos above show the graceful outlines of the
rack tails. Notice external and internal toothed meshing surfaces for the
hour and quarter rack tails. We needed this since both racks operate in the
same reciprocating direction but need to mesh with pinions attached to fly
fans which will turn in opposite directions to each other. We do this to
maintain the the left-right 'handedness' of the three paired fly fans in
this movement. They are the two remontoire, the strike and these rack let
We now begin the hour rack lifting pawls using the same
allegorical bird design used for the quarter rack. First the rough parts are
made and the pivots inserted in the appropriate places. The third photo
shows the assembly in the movement to test for fit. Next is a drawing
depicting the final outlines to be cut for the pawls.
Once again these parts are cut with the hand fret saw. The
next two photos show the completed assembly in place. The last photo shows
an additional lever attached to the quarter rack tail which is used to
release the hour rack at the end of the quarter strike sequence (part
attached to lower jeweled roller). When the quarter rack is near the end of
the sequence it puts that additional rocking lever, which has two pins, into
a position where those pins simultaneously pull away the pair of bird pawls
(not shown) holding the hour rack in place; allowing it to fall and begin
the hour strike sequence.
The strike lever work is now complete. The large and
numerous jewels within these assemblies are a nice touch. The feathers on
the strike detent birds are only a preliminary trial of seeing how we will
attach these detents to the racks. If one looks closely at the quarter
strike (right hand) bird's feathers, and last photo close up, you can see a
pin protruding between the uppermost and next lower feather. This pin is
connected to the quarter rack tail and moves that detent downward until
intersects the fly fan's whip.
Below are three YouTube videos showing the strike trains and
the action of these linkages and their epicyclical fly fans. Depending on
your security settings you, may need to allow your browser to run
active-x controls to see these videos. Otherwise you can visit my YouTube
channel at: http://www.youtube.com/user/fgtyc