The escapement mechanism is the most dimensionally sensitive part of the clock. The pendulum controls the rocking motion of the escapement pallet on its arbor. In turn, the pallet allows the escapement wheel to rotate one tooth at a time. To work correctly the following dimensions have to be correct:
- Distance between the pallet and escape wheel arbors.
- The shape of the pallets.
- The radius and width of the scape wheel teeth.
Nothing is perfectly accurate and I deliberately cut the escapement wheel teeth to be longer than required and then trim them to the length needed to for the escapement mechanism to run. The photo below shows how the initial, over length, escapement teeth results in the pallet arms not letting the escapement teeth pass.
I use a dial indicator jig and the Zenbot CNC router to check and trim the escape wheel teeth. The first step is to use the dial indicator to find the shortest tooth and then adjust the router cutter to just touch this tooth.
I then turn the escape wheel by hand through the cutter to trim them to the same length. I then checked to see if the escapement still binds. It did not and I returned to the CNC router to trim 0.005” off the tooth, re-checked if the escapement worked and repeated multiple times until the escape wheel just passed through the pallet arms.
Some of the teeth still rub on the pallet arms as they pass through, so I suspect that I will need to trim more off, but I did not want to trim too much off as this results in a clock that has a loud tick-tock.
Next, I made three 1/2” diameter brass collars. These will hold the hour hand, minute hand and secure the end of the great arbor.
Finally, I cut the arbors and the brass bushings for the wheels give 12:1 gear ratio between the hour and minute hands.
I received an email from Hobby Metals telling me that the 3/4” diameter brass rod that I ordered has shipped. Should arrive on Thursday. 😊. I am not sure what to tackle tomorrow. Although the CNC router gives a good surface finish, I still need to sand every gear tooth. This is a mind-numbing task ideal for doing when listening to a Cincinnati Reds baseball game. With no baseball, I guess I will do it while listening to Corona virus news. I also have to cut the clock hands. I will decide tomorrow.