I am hoping to get started on the Crown Wheel next week and I was just mulling over an issue I had with the wooden version of the clock. Before that, a reminder of how the crown wheel and verge and foliot work together... This is taken from the Wikipedia entry for Verge and Foliot
In my clock the Crown Wheel will be turned 90 degrees from what is depicted here. In other words, the arbor will be horizontal rather than vertical. It will also have 33 teeth. In addition, the verge and foliot (the bar in the top of the diagram) will be vertical rather than horizontal. The way this works is that as a weight turns the crown wheel, it catches one of the pallets (letter q in this picture) and that rotates the verge and foliot. Then, just as the Crown Wheel rotates one of the pallets out of the way, it catches the other pallet and it has to rotate it the opposite direction. This repeats over and over. So the Crown Wheel is always trying to rotate the same direction but to do so, it has to rotate the verge and foliot one direction, then the other. This oscillation is the "tic toc" of a medieval clock.
Anyway, in the wooden clock that I made, I had a lot of trouble getting this to work. The problem was that sometimes it would jam or skip teeth in the Crown Wheel. Sometimes the pallet would not swing into place in time or it would swing into place too early. Fine adjustments with sand paper was required to get it to work properly. Even then, variations in humidity affected this.
I think when I made the wooden clocks, I was trying to have the pallet engage the Crown Wheel as soon as the other pallet released the Crown Wheel. In other words, it would already almost be touching. I think the solution is quite simple. I am going to try to design it so that there will be a significant gap (maybe about 1/8 to 1/4 inch) when one pallet disengages to where the next one engages. This should cause a suddenly slip in the Crown Wheel as it rotates that gap to engage the other pallet. It will also lead to a more distinctive ticking.
If you don't understand this, don't worry. I just made this note because I've been mulling this over and I wanted to get it down on paper and make myself think it through.
2 comments:
It seems that the extra gap would indeed improve the action of the verge and foliot- but the trade-off could be increased wear at the bearing point. A good case-hardening would probably fix that, sometime after the clock was "run in". This sounds like it would be EXTREMELY similar to fine-tuning the sear in a flintlock.
Glad to see you back to work on the clock!
I don't think that should be an issue. The Crown Wheel does not have enough time to build up momentum. In order words, I don't think the overall force would be that great. But who knows? I've never done this before... :)That is one of the nice things with this version of the clock. It will actually be easier to fine tune than the wooden one... One of the few things that will be easier.
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