Continue celestial train demonstration drive, finish transmission, begin orrery output gearing - October 2013
This month we continue to fabricate the drive needed to manually demonstrate the various celestial functions of the clock in both forward and reverse. The first section of this installment finishes the two speed transmission. The second starts the output gearing.
This month Buchanan has begun to fret out the spokes for the celestial demonstration drive's two speed transmission. The fourth photo shows the main output shaft that will connect to the orrery output gearing.
Next we have the associated contrate wheel fitted to the output shaft. The third photo shows the underside of the plate with another drive bevel wheel. Both of these wheels are used in the differing speeds for the transmission's output.
These photos show the action of a ball clutch within the transmission shaft. In the first photo one can see the inner, beveled shaft within the hollow tube shaft. Next we see the ball clutch installed. Depending on the position of the inner rod that ball will either retract or protrude above the surface of the outer hollow tube's surface. The inner rod is shaped in such a way as to keep the ball permanently captured at this location. There are four of these in the transmission.
The first two photos show how the action of the ball clutch will either allow the sleeve surrounding it to rotate as in the first photo, or be held stationary as in the second. The next photo clearly shows the machined lobes which mate with the ball clutch. Next a roller bearing and ring mounting are fitted.
In this series of photos the transmission is built up. the last photo has the end of the transmission shaft protruding out from the front frame. One can clearly see the inner rod within the hollow tube.
Here the transmission is put into the movement for its trial fitting.
The escapement plate containing the output contrate and bevel wheels are fitted above the transmission. The vertical arrow shows the transmission bevel which engages the output bevel located below the escapement plate (hidden by plate in this photo, but clearly shown in the eighth photo in this installment). The horizontal arrow points to the transmission wheel which engages the contrate wheel through a slot in that plate above the escapement plate, (barely visible behind strike carousel cam). That slot is clearly shown in the fifth photo in this installment. We now turn to the next phase of the celestial demonstration drive, the orrery output gearing. One could be forgiven for assuming that there is a simple direct vertical connection from the output contrate and bevel wheel shaft up to the orrery. It is, after all, located directly below where the central shaft to the orrery is planned. However, as is the case with many of the design features in this project, there is usually a complication thrown in. We need the output gearing to perform two functions. The first is to reverse rotation of the final output shaft to the orrery from that present at the bevel and contrate drive wheels. The other is to obtain the correct gear ratio for the orrery. The period must be changed from mean solar to sidereal time. Could this have been done more efficiently? Yes, but certainly it would not be as visually interesting and beautiful.
The first photo shows a plastic mockup of the gear set proposed for the orrery output gearing. Five of the seven wheels needed are shown. One immediately sees the design as bridge raising the wheel set up and over the adjacent escapement antifriction wheel pair. The mockup allows Buchanan to check for component conflicts within the increasingly crowded machine. The next four photos show the mockup placement.
First the rough wheel blanks are cut out of the brass flat stock on the jewelers saw. Next they are turned into blank gears; the same procedure as has been done for the over 120 wheels that have already been fabricated.
Next a free-hand drawing is produced for the two cocks that will be used to suspended the upper wheel set bridge. It reflects the curvilinear ivy style seen throughout the structure of the movement. Next is a paper cutout of the proposed fretting for the escapement support plate. Note how much of the bulk of that plate w ill be eliminated. This is the last of the original blocky, rectangular plates comprising the initial clock frames which were made in January 2010 before the internal works were transferred from the temporary plastic frames to the permanent metal ones.
The center photo's circled area and the red arrow in the next photo show the original escapement support plate made in January 2010 as described above. This is a good time to look back and contemplate how far this project has come!
Next the paper templates are positioned where the final parts will be. Buchanan cuts the escapement support plate on the same jeweler's saw that has been used on all the flat stock in this project, including the spokes for all of the wheels, the swirled escapement wheels and the filigree pendulum balances.
The escapement support plate is put into position. Notice how this really opens up the area below to light and inspection. Of course this is then a bit obscured when the escapement and the associated antifriction wheels are mounted, but more wheels are just fine by me.
Now the two cocks which will hold the orrery output drive wheels are cut from brass stock.
Next these are mounted onto the inner celestial train frame pillar to test for fit and alignment. The two completed cocks and escapement support frame are then jeweled. Look carefully at the first photo and count the number of jeweled bearings, there are twelve, plus the eight yet to be installed in the two cocks and escapement support frame shown in the second photo, more in this one shot than in a good quality watch or fully jeweled clock movement. But can you tell the ones that are actual jewels and those which are hiding caged roller bearings? The answer is there are seven caged bearings and 13 jeweled pivots.
Two of the jeweled pivots close up. Next Buchanan begins the compound wheel that drives the orrery output gear set. This wheel is both a conventional and contrate wheel; one mounted on top of the other.
Once again Buchanan has created an elegant component that is both functional and beautiful.
Buchanan now begins to fabricate the wheel works for the orrery drive. In the first photo the large cylinders are the blank collets upon which the wheels will later be secured to. Next the blank wheels are tested for fit. Next begins the process of spoking the wheels.
Here we see the fabrication of the hard, tool steel pivots for each jeweled bearing. These are inserted into the end of each arbor. The reason why we cannot use the common practice of of making this from a single piece of material is that this movement used stainless steel for all of the arbors. Stainless is too soft and has poor frictional properties in that it is a 'sticky' metal, entirely unsuitable for bearing material. However, it will polish to a beautiful finish and more importantly will not corrode. I have seen too many wonderful skeleton movements that have flash-rusted arbors because of one unfortunate event where humidity was allowed to become too great for a period of time. All other silver metal in the clock will also use stainless, only blued material will use conventional steel since stainless will not blue properly. It is our intention to run all of these types of pivots without the use of oil. Dry jeweled bearings are used in applications where the arbor is lightly loaded and will turn at less than once per hour. Arbors that have greater loads or rotate more quickly use caged roller bearings. At this point we are using conventional roller bearings, but for the final build these will be swapped out for full ceramic bearings which require no lubrication. These in combination with the dry jeweled bearings and Harrison's grasshopper escapement will allow us to make this machine a 'dry runner'. Degradation and contamination of oil is the number one reason for clock failure over time. Breguet is reputed to have said in the 17th century, "Give me the perfect oil and I will give you the perfect watch." What was true then is still true today. I know this is quite controversial; we are breaking new ground here to apply these principals to a machine of this complexity and mobility, and comments are welcome.
This represents the number of screws needed for the orrery output drive, about 70. All screws used in this project are custom made, there are no "off the shelf' screws. As one might imagine the number of screws will reach into the low thousands. Below are two videos which show in real time how Buchanan makes a screw about 60 seconds a copy.
http://www.youtube.com/watch?v=J8vUfLGNfvM&feature=player_detailpage&list=UUXfBC8kwQoIupflS7aD8H_A
http://www.youtube.com/watch?list=UUXfBC8kwQoIupflS7aD8H_A&v=bnoztEvCDrk&feature=player_detailpage
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