Horological Meandering

I was wondering if someone could share thoughts on the issue. Can a watch be too small or too big to maintain time well.
Is there a critical size beyond which a movement will not work well.
Many thanks

...No time now forgive me. I hope to return to this soon.

In a nutshell, bigger allows more room for more energy storage (spring), larger heavier balance wheel etc. If this energy advantage is released over a normal duration (e.g. 50h) through a higher inertia and/or higher frequency balance rather than simply to give a watch a long endurance (e.g. 8d) then this usually results in a watch with better stability of rate. Unfortunately, movement sizes have not generally kept pace with the space available in the current crop of big pieces (>42mm for example ;-)) to take advantage of this.

Velociphile

As Velocophile says, bigger means more space for larger main springs and bigger balances. Bigger balance means more inertia which means more immunity to shock and more stability of oscillation (higher Q). Locking/unlocking forces can be higher which also adds to stability. Larger components means that tolerances are less of an issue and that manufacturing, assembly and repair are easier and can be more precise.

I'm not sure there's an upper limit. The observatory competitions had categories for marine chronometers, deck or pocket chronometers. The original categoiry A was for pocketwatches 43-70mm in diameter, and the category D for wristwatch movements 300mm in diameter only appeared in 1943.  You can argue that a marine chronometer is not quite the same because it uses a different escapement that's not suitable for a watch (modern AP version of the Robin excepted), but marine chronometer-sized movement with an anchor escapement will always have the edge of a wristwatch movement.

I feel like being contentious (for a change ) and stating that a wrist watch movement will never attain the performance that a large pocketwatch movement can get to if the same technologies are used.

nick

Being the geeky sort I created a little spreadsheet calculating the power of the oscillating balance and the energy store in the spring. As usual the old Rolex calibres are in the lead (based on my limited data set of balance wheel intertias - yes, I collect them; note to self, get out more in 2006) being 15 mgcm2 beasts and of course they oscillate away at the benchmark 28800 vph. Now assuming a given amplitude (may I?) we can compare the power delivered to the balance wheel/hairspring as a function of its inertia and frequency (cubed).

In relative units, if we make a Rolex 3135 100,
A JLC autotractor with a balance of 14 mgcm2 at 28800 vph gives us '93.3'.
A RM003 with a 10 mgcm2 at 21600 vph is '28.1'.
A JLC 8 day wheel of 3.8 mgcm2 going 28800 vph is '25.3'; a quarter of the power of the Rolex.

And of course, we can see how an 8 day movement can be delivered more easily with a lower power consumptive balance. Which brings me to the next step: the gas tank, the spring. So, we take the power reserve and power consumption multiplied together to give us the required energy store size, the size of the gas tank the size of the spring barrel(s).

Again taking the examples, we have Rolex '100' runs for what, 50h. So we'll call that '5000'.
The JLC autotractor=93.3 * 50ish=4665.
RM003=28.1 * 70=1967.
JLC 8 day=25.3 * 192 (9 days?)=4863.

So arguably despite all the fuss about twin barrel etc, in fact the energy stored in the spring pack of a Rolex 3135 could have powered the JLC 8 day. Hmmm.

So naturally, with a spreadsheet you can begin to perform some what ifs and investigate some truly marvelous and preposterous scenarios. What you notice however, and that dawns on you as obvious in retrospect is that for a given spring pack energy storage value, dividing it by the number of days reserve gives you the 'power budget' to expend in your balance combo; be it small wheel with higher vph or big wheel slower vph.

If we assume that the spring in the new ND58 43200 is comparable to the Rolex (and why not?), then with the 42 hour P.R. we can see that at 43200 vph, Seiko would have a 5.3 mgcm2 wheel (quite small). Returning to the above analysis, the ND58 would score '119' beating Rolex by ~20% on balance power! And of course, it's naturally at the expenseof power reserve (42 versus 50 ) for the same notional spring performance. (i.e 119*42=~5000). So let's go further. Who's got the biggest most impressive spring? Well, to cut a long story short AFAIK from my data, the Freak is right up there. It powers a 7mgcm2 balance at 28800 for 168h (am I right?), so if we take that baby what do we get? Well if opt to stay at 42h power reserve to maximise out balance power, we can have a 8.3 mgcm2 balance at 43200 vph. Now that, ladies and gents, would be a '187' relative to the '100' for the Rolex. I believe it would be possible to do something quite signficant with the accuracy and stability of a watch with such a high power balance operating at such a high frequency. Here's hoping for further developments.

I even propose that 1 + 1 will never add up to exactly 2.

Because the numbers themselves wear out !!!

Entropiously yours ))

amerix

I suspect that inertia is only part of the story.  It gives you a lot of advantages in a watch that will be shaken and stirred, but there are other factors that come from having a physically larger movement to play with.

In precisions clocks, one of the key things to master is the "strength" and consistency of the restoring force.  The idea being to give the lightest possible shove t keep the pendulum moving, but without going so small that you can't control the impulse.  If you can't control it you can get it consistent and the oscillator suffers.   A precision clock might have a couple of kilos of pendulum bob moving through a degree or two of arc, being impulsed by a gram or two falling through a couple of millimeters.   This is a ratio of impulse to inertia that's many many magnitudes beyond that of a watch. 

There's also the point of making the oscillator do the least possible work to trigger the impulse.  The more work the oscillator has to do to trigger its impulse, the more it's disturbed, adn the more inconsistent the unlocking force, the more the oscillator suffers..   I'm guesing that the unlocking force for the anchor in a small movement is not significantly proportionally less than the locking force of that of a larger movement, but I could well be wrong (no data).

I suspect, but don't know, that you can get a more controlable impulse with a larger movement, and that the impulse can be smaller relative to the inertia as there's proportionally less energy being lost unlocking etc. 

You only have to look at the major improvement in timekeeping from moving to a chronometer escapement to understand the disturbing influence the impulse has on the oscillator.

nick

with regards to the beat rate will even it out and make the accuracy of the movement less prone to being influenced by spontaneous shocks and wrist movements.

That much being said, I love large balances and a slower rate of 18,000 to 21,600 bps because I can experience more of the watchmaking tradition, with hopes that more young watchmakers will find their way into this passion and lifestyle than if they had been trained to assemble and be adopted by and for a particular brand.

A very personal view, and with due respect - and admiration - for some furiously fast-beating watches!

amerix
This message has been edited by amerix on 2010-05-20 08:14:01