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Geneva Stop Work
The Geneva Stop Work known also as Maltese cross was a major contributor to timekeeping accuracy in both Watches and Clocks. The stop-work mechanism when used with older high carbon steel springs effectively ‘clipped’ or disengaged the end portions of a mainspring where extreme torque variation occurs leaving the middle much more constant torque flat portion of the mainspring to power the gear train.
This simple easy to manufacture design made the Geneva Stop Work an inexpensive, commonly encountered improvement on both watches and clocks.
I tried to show as much as possible using animation so I hope this is helpful for anyone wanting to know more about how this facinating mechanism works and how to go about setting mainspring pre-tension.
Enjoy!
This video covers:
- Geneva stop work purpose
- Theory on why ‘clipping’ the torque off of the ends of the mainspring is important
- Ratios
- Setting up mainspring pre-tension
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Thank you for your excellent video.
Please could you explain one thing to me after setting the pretension from the bottom end of the spring that is putting on one turn of preload onto the main spring will this also have the effect of removing the final turn of the mainspring? Or is that done in another way? confused
Good to hear you liked the video Malcolm!
Yes you’re correct. In the example I use in the animation, pre-loading one complete turn of the mainspring at the bottom end will automatically clip a turn at the opposite end. When winding the timepiece the convex face will come into play after four complete turns of the winding key/crown. This also applies to loading by backing off one turn from full wind and then setting the stop. The Geneva stop will take care of the opposite end.
Important to understand is that the mainsprings maximum usable energy and torque is never wound into the barrel. When winding the watch/clock the last turn will be stopped by the convex face allowing only five winding turns (the one pre-load plus the four turns allowed by the Stopwork) to pass into the barrel. Result is use of the flatter portion of the torque curve and less overall tension on the spring when the timepiece is fully wound.
Wow, great video; thanks!!!!!
Recently, I was given a 1904 Seth Thomas School House clock that runs as well as the day it was made and keeps perfect time.
I was just wondering about how tight to wind it, so as not to break anything or put too much torque on it, and how long it was designed to run when fully wound.
I have an 1896 Elgin Grade 27 W B Raymond watch. I did a tear down and rebuild last week and found the winding index in place but nothing on the post that was there. I hadn’t lost anything and was confused as to what might be missing until I came across a video by C S Spinner with him doing a Swiss watch that had both parts in it. Now knowing the names I asked him about its purpose and he directed me to your site. Loved your explanation and video.
I guess someone in the past lost or removed the star wheel. I have put the watch back together as it was with the winding index in place.
If I want to find a replacement star will it have to be from an Elgin of the same grade or would any Elgin star wheel work? Not having the original, I don’t know how many teeth it should have. Do you know of a source for that kind of info or should I just leave the movement the way it is without the star seeing as I am not trying to keep trains on time with it?