Bulova 11AF Will Not Run
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By nevenbekriev · Posted
OK, a little bit more from today's lecture about the main springs. Generally, the spring in the barrel is limited and can't unwind fully. With the blue line is shown the reserve/torque relation when spring unwinding is limited by the barrel. The green line represents the same when the spring is free to unwind fully And the red line shows the minimum torque that is needed for the movement to keep running. The yelow graph shows how the torque changes (from the blue) when the spring gets weaker (set) after 100 years of work. The purple line represents thinner and longer spring in the same barrel. As You can see, using thinner and longer spring will increase the power reserve. The 'set' spring will have the same reserve as a new one with the same sizes, only the amplitude will be just a little smaller. Of course, this is true only when the movement othervice is in good health ( the red line is lo enough) -
By rjenkinsgb · Posted
As long as you don't grind the stuff up and blow it around, you should be fine. Use a dust mask if in doubt. The things I'm very careful of are: Radium lume - even the stuff that is visually completely dead and inert is still highly radioactive; it's the fluorescent part that decays, not the radium. A single speck inhaled or ingested can cause cancer, so store parts in zip bags and wear a dust mask & wipe your work area down after handling anything that uses it. A proper geiger counter is a good investment if you plan on working with vintage watches, so you can check for it & take appropriate precautions. "One dip" & equivalents - the original type & the generic PERC dry cleaning fluid (Tetrachloroethylene / perchloroethylene) which is what the original one dip was mostly made of. That's toxic, a known carcinogen. Use in very good ventilation only & keep it sealed whenever possible. The newer B-Dip is presumably a safer replacement. -
By Neverenoughwatches · Posted
Only 137% ! sounds like you're not putting enough effort in 😆. I would think of it like cogs on pushbike. Fastest speed to the spindle would be largest pulley wheel on the drive and smallest pulley wheel on the driven. If the motor was into a sliding bed you would have 3x4 ? Speeds. -
By rossjackson01 · Posted
So please we have that comment. Eccentric59. Great work. -
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Thanks @nevenbekriev. I did some further reading and I think I kinda understand it now. Basically, if you were to fully fill the entire barrel with a super-long mainspring, you can't actually wind it anymore. Hence zero power reserve. Likewise the other extreme (mainspring too short to be wound around the arbor). This explains in very basic turns why there is a sweet spot in the middle of the curve you drew. Importantly, this is relative to the barrel diameter (and arbor diameter). In other words, if you have a larger barrel you should have a longer mainspring and hence also longer power reserve. So Longines' statement isn't entirely wrong (longer mainspring = more power reserve). BUT you can only make the mainspring longer if you also increase the barrel diameter. Thanks again for making me think about this a bit more and learning something. That's why I love this forum! However 😉, there is still some truth to what I said (I think! Please correct me if I'm wrong!): according to my reading, the key parameter is the share of the space between barrel arbor and barrel wall. Half of which should be occupied by the mainspring (based on Theory of Horology by WOSTEP, quote in depth here: https://www.vintagewatchstraps.com/mainsprings.php). The space occupied by the mainspring in the barrel is a simple function of mainspring length AND thickness. This implies that increasing length, but keeping the same thickness, will lead to occupying too much of the barrel space and hence reducing power reserve. This is what @nevenbekriev 's drawing correctly shows. However, if you increase length AND decrease thickness in the correct ratio, you can maintain the correct mainspring proportion vis-a-vis the barrel (i.e. occupying half of the space between arbor and barrel wall). This would indeed lead to an increase of the number of barrel revolutions (when unwinding) and hence a potential increase in power reserve. However, you loose torque. And a loss of torque will also lead to the watch stopping earlier (when torque can't overcome the friction in the gear train). Thus, these two opposing effects may cancel each other out. Which again makes this statement probably true: FINALLY, we still want to help @Zendoc with his very concrete decision: GR4485 (same thickness but shorter than original) or GR4477 (slightly thinner and a bit longer than original). I would still advocate (considering modern lubricants and potentially stronger metal alloys -- and consequently the risk of knocking at full wind) to choose the latter.
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