Monday and part of Tuesday, I finished up my work with the crib toy. When I left off last week, I was just getting started with the roller jewel and corner clearance. As with each step in the process, the important part is making sure you start with the pallet stones and go up from there. If the stones aren’t set in the proper place, the shank of the fork won’t be straight and that will impact/impeded progress with getting the roller jewel in the right position.
Besides delivering the impulse to the pallet fork (from the balance wheel), the roller jewel can serve as a form of shock protection. I am going to jump ahead for a moment, but it will help me explain the shock protection of the roller jewel. Most modern watches use what is known as a safety roller. The safety roller is an added disc that limits the movement of the pallet fork by interacting with the guard pin. When there is a shock to the watch, the guard pin will move forward a bit and touch the safety roller ensuring the the integrity of the lock between the pallet stones and the escape wheel teeth. The roller jewel can do the same thing if you have the proper corner clearance.
When you are adjusting the roller jewel, you need to make sure that it isn’t too far back or forward on the roller table, as well as making sure that the roller jewel is centered to the cut-out of the safety roller. When you have the proper “vertical” placement (how forward or backward it is) as well as the correct orientation, when the roller jewel makes its arc through the pallet fork, it will have an even amount of spacing between the jewel and the horns of the fork when it enters and exits the space between the horns of the fork.
After adjusting the roller jewel, the next step in the crib tool process is the guard pin. As I said earlier, the guard pin serves as a safety mechanism. The guard pin on the model can be adjusted both forward and backward, as well as rotating right and left. When adjusting the guard pin, you want to make sure that when the the roller table is rotated around with the finger out of the cut-out (see the picture below to see the cut out in the safety roller), you want the guard pin to be almost touching the safety roller (on both sides of the cut-out)
Finally, the last step with the crib toy is to adjust the banking pins. The banking pins serve to limit the lateral movement of the pallet fork. If the pallet fork didn’t have banking pins, when it received the impulse from the roller jewel and went as far as it could to one side, there would be a lot of wasted energy to move the pallet fork all the way in the opposite direction. Lets not forget, increasing efficiency is one of the goals of watchmaking, which is why things like the Cartier ID 2 and the Girard-Perregaux Constant Force Escapement have been made (look for a post later about these watches). They (banking pins) also serve as the way the pallet stones and escape wheel move from the initial lock phase to total lock (a very small difference in distance, but it is significant).
After getting the banking pins set, it was time to take what I had been practicing (regarding the pallet fork exercises and crib tool) into some “real” world scenarios. I was given an ETA-6497 movement and had to remove the pallet fork stones and them replace them while making sure they had the proper amount of lock. The removal went fine, as did the shellacing. The first time I did it, I had too much lock with the exit stone. After adjusting the depth of the stone (took it out, cleaned it again and put it back in and re-shellaced it), I put the stone in and thought it was good. Once I took it up to be checked, it was brought to my attention that I had the direction of the exit stone reversed. Surprisingly, the watch still ran, but just not efficiently (when I put it on the timing machine, it had a slight loss in amplitude in the crown up/down position, but I can’t attribute that for sure to the pallet fork. Once I got it flipped and put in the right way, it was time to strip down the movement, get it cleaned, oiled and put back together. I got the cleaning done this morning, was in the process of getting it oiled and put back together, but I managed to snap the lower shock jewel spring (I was warned by pretty much everyone who is in their third and fourth semester that I will have that happen a couple times). I got a replacement spring put in (rather quickly) by my instructor, and I’ll finish oiling and re-assembling the movement tomorrow morning. After the 6497, I am pretty sure I’ll have some smaller movements to do the pallet stone adjusting with.