Planisphere mask, finish bezels and misc. demonstration mechanics
This month Buchanan creates the planisphere mask. This marks a
milestone since this is the last mockup component, other than the dial
hands, to be fabricated into metal.
The first illustration is the CAD graphic for the computer-controlled
mill that will create the planisphere mask. Here is an application where a
one-off part still makes sense for the time it takes to program the machine
because of the complexity of the part. The engine-tuning and net as well as
the engraving all contribute to this. The next photo shows a test run of the
I can't remember exactly when I had decided to have this Latin inscription
added to the clock, but I had first seen it in a small pamphlet written
about the astronomical clock in Strasbourg, France by Jean-Baptiste
Schwilgué, in 1843. I had purchased
the pamphlet sometime in 2006. The design for the Sun & Moon rise-set module
was begun in late 2016 and at that time it was decided to use the unique
variable differentials used in the Strasbourg clock for the Moon's orbital
anomalies. It may have been at that time that I began to look into my
reference material on the clock.
The phrase was part of an epic poem, Metamorphosis,
Publius Ovidius Naso, commonly referred to as Ovid in AD 8 and is translated
“To man God gave an upwards gaze, bidding him to behold the
sky, and raise his erect countenance towards the stars.”
When taken in the context of the poem it is when God separates Man
from the animals by giving him the ability to stand erect and gaze toward
the heavens, presumably to unite him with God in contrast with the downward
earthly gaze of animals. Obviously Ovid was not familiar with primates! But given
when he lived and that he was from Greece that’s understandable.
The font chosen was Century Gothic seen in MS Word.
I thought this to be appropriate as the planisphere represents the night sky
with the stars that Man would observe in the poem. In fact the entire
machine is a small encapsulation of God's creation as experienced by Man at
several magnitudes. There are the stars as seen from the ground represented
by the planisphere, then the Moon and Sun within the tellurion and the Sun &
Moon rise-set module above it, and finally the Earth's neighborhood as
represented by the orrery that crowns the machine.
Begin the planisphere mask
The planisphere mask is
now started. The mockup model is fabricated of Corian and spray painted a
gold color, on the left, and was seen in the
May 2018 installment,
and has the distinction of being the last mockup piece to be made into its final metal incarnation.
In the first photo we see the beginnings outline of the planisphere
longitude and latitude net. Next the net begins to appear as the cutter
pierces below the back side surface.
Now the lower area is being
prepared for the diamond engine-turned pattern.
Next a detail of the
A close up of the diamond pattern engine turning similar to that seen on
Breguet's watch dials.
The planisphere mask is now fabricated from the mill and is ready for final
hand finishing. Doesn't look like it needs it does it?
The first photo shows the silver sector dial being engraved. Next the
dial is engraved and black dial wax filled into the lettering.
Today I finished the ring for behind the mask. I started with a bent up and
silver soldered ring glued to a face plate, first photo. Then I parted the
ring from the face plate photo, second photo.
This gives a perfect cut to the side that was glued to the lathe's
I had to machine a locating groove in the back of the mask, third
photo. And a matching raised locating ridge in the cylinder photo, fourth
The mask and the ring will be held together through a flange created by
milling the rest of the interior surface of the ring. This is the reason the
original ring was made from a thick material.
These four photos show
the drilling and tapping of holes for the screws to secure the mask to its
Progress on the mask today.
First photo, machining the outside to size. Second photo, machining the
curve on the inside of the upper moulding.
is the embryo upper cornice. The inner section is milled to conform to the
cylindrical portion of the mask. Then the gap is filled with’ body filler or
Bog’ as it is known here
before cutting the rear profile to match the main clock base Next, cutting
the recess for the movement.
getting there. And last, drilling the fixing screw holes.
The first photo
machining away the back profile of the ring's decorative molding piece to match the main
base's upper cornice of the clock, it also
had to be mounted in a groove, yellow arrow, and clamped down inside a
channel, red arrow, to stop it falling apart under the cutting loads. There
is not one square flat face that can be used for proper clamping. Next photo
the planisphere main support is dowel pinned to the base frame to preserve alignment,
First photo is the trial fitting on the
clock. Super glue holding the intermediate plinth in place so that it can
find the correct screw position. Next Buchanan screwed the intermediate
plinth to the base prior to final alignment and pinning. This is all
necessary to keep the adjustment pinion in mesh which will be mounted on the
The first photo shows the final molding, one can see
there is no proper reference face to hold it with when machining, see fourth
photo prior. The next steps are to trim the upper cylindrical section of the
mask to clear all the gears behind it and also the whips of the Fasoldt
flies. Then the final polishing of the mask and the web.
for once things work out well. The scroll saw can fit inside the mask. Next,
the start of hand fitting the mask to the base. Measurements and scribe
lines help but it is just cut and try in the end.
Next two photos, getting there and then extra-long counter bore so that the screw
heads will be recessed to make final assembly possible.
I have measured and drawn the spacing of the demo select lever. We have 19
degrees of movement between each selection position or an inch and 1/8
spacing on the rim. I made a paper mock up and took some photos, (above
and below). Please remember that there is also a cut out for
the setting window and we only have an inch for the script. I am racking my
brain for an elegant way to fit a pointer though. I think it is the correct
place for the demo plaques though.
The second photo shows the Corian mockup that has the star field calendar
setting window cut out behind the three paper mockup windows.
The three tags represent the selector for the demonstration function.
The first is when the machine is in normal operation CLOCK DRIVEN, next when
all of the celestial modules are being driven together, CELESTIAL
DEMONSTRATION, next when only the orrery is being driven in high speed (12
times the speed of the prior demonstration), ORRERY DEMONSTRATION. The
window behind the three mockup tags is the setting calendar dial for the
star field and is already designed and cannot be altered.
The same three mockup tags on the fabricated planisphere in the first photo,
note the star field calendar setting window has not yet been cut. The second
photo shows the solution that was adopted.
Buchanan could not put
the selector tags on the rim of the planisphere's body, there were obstructions that
could not be surmounted and so the proposal is to have a sector dial behind
the planisphere, on the same plane as the spring duration dials. This,
however has also proved impossible, so it is one issue yet to be resolved.
Perhaps a small semicircular sector dial can be placed above the square
selector keyway with the letters C, D and O for Clock driven, Demonstration,
and Orrery. In this way someone who is unfamiliar with the mechanism will
know immediately that this is a selector and not a conventional winding
square meant to be cranked all the way around.
The first photo shows
where the original setup of the Sun setting clutch was. This would allow the
user to move the sun hand around by manually grasping the sun arbor. The
problem is that this was made without taking into account the net that now
covers the area where the sun can be see and so makes it impossible to set
it in this way. The second photo shows the two wheels that are positioned
directly above the planisphere. Here is an instance where Buchanan's
serendipity came into play.
In this photo we see
the new Sun setting arrangement, yellow circle. The knurl knob, clutch and
the new wheel arrangement is seen in the second photo above this one are now
assembled above the planisphere setting window. Buchanan just needed to
split the arbor that the two wheels were fixed to and put the clutch between
them. Now when one turns the knob the Sun moves, but when left alone,
the wheel directly behind and clutched to the new wheel will drive the Sun
in normal clock time mode. The second knob, white circle, adjusts the
planisphere star dial and is set through the window aperture.
The longitude and latitude net is now hand finished
Because the web is so delicate I had to make a backing support plate.
Fortunately I had the machine code that I could slightly modify. I also made
a secondary plate with a recess so that I could spin the support plate on
and it is always over a hole.
We now turn to the
refinement of the mask net. Look carefully at the photo, while the net is
very nice, it has a flat top and side profiles. Here is where
Buchananization begins, to take something that is good and make it great.
The mask net is placed over a substrate made of Corian to the exact outline
to support the net for the hand finishing to be done.
The net before the hand finishing is fitted over the support
substrate. Note the straight, blocky profiles of the webbing.
In the first photo Buchanan uses a set of calipers to show that
about 50% of the mass of the web is reduced. Both the vertical sides are
reduced by tapering these toward the top. The remaining part on the top that
is flat is given a rounded profile.
The last two photos above show the difference between the ‘before
and after’ effects of the hand profiling. The photos show on the left the
finished web compared to the unfinished on the right; and the corresponding
reduction in the thread profile.
Buchanan writes: There are 4 rings of 16 holes = 64 holes in the web.
Each hole has 4 sides = 256 sides. Each side has a top, bevel and side to
polish. Total of 1024 facets, and 256 bevelled corners. If I can finish a
facet in one minute it comes to 17 hours. And I have just started.
this type of attention to detail that makes the clock so special.
The mask is truly a stunning asset to the machine. The grid is so
delicate and reflects the light beautifully. Where they intersect is lovely.
Even up close under magnification the millwork is perfect, Breguet would be
proud! The Latin inscription is nicely proportioned and lends a bit of
mystery. The tiny screws holding it are so fine as to be just about
planisphere mask. It should be noted that the dial itself is still a paper
photocopy mockup, the enamel dial will be installed only when the entire
module is finished.
Two three-quarter views of the planisphere installed on the clock.
Front elevation of planisphere module.
The entire compliment of enamel dialing with their bezels completed.
Compliment of bezels now ready for gold plating. Another refinement to the