I have a 9j Wlatham 6 seconds stop watch, used by Royal Navy durnig the II WW (if you want to see it in detail, please check
Waktham PATT. 6
I am puzzled by the outer area, tooled like almost a wheel, with small teeth, as per the following picture. There must be a reason for working it in that way, but I can't figure it out. Could you kindly give me some hints ?
Have a nice weekend and a thousand thanks !
balance wheel detail

Oops ... you can see it clearly in picture 19 ... sorry

Mario

The reason for this unusual shaped balance wheel is the stop mechanism. Look at picture 14. The stop is bow shaped and could act in both directions of the balance swing. If the watch is stopped it is a bit of a sliding action when the stop touches the teeth it is like a brake slowing down the balance speed and then stopping it. Imagine a poising screw : it would stop at once; a flat rim would slide too long. The balance is of a 'high speed' type, the hairspring is stronger than normal, the lever is moving faster. I think a sudden stop would give a (too) strong impulse to the most sensitive impulse stone and balance pinions. (my thoughts)

Regards,
Gerald

Gerald, many thanks ! Loud 'n clear, I had not thought to the very basic fact that you have to ... stop a stop watch. It is true that accelerations there are quite big, and F=m*a, so you have to balance wisely things or all will end in pieces very fast. Old watchsmiths, with no CAD systems and no computers do were knowledgeable persons. The more I get to know old movements, the more I admire them. Thanks again for your cristal clear explanation.
Have a nice weekend
Regards
Mario

BTW, Gearld, I added your explanation, under your name, in the description of the stopwatch. Thanks again
Mario

Mario

I've just noticed. Cute gesture, I'am pleased.

The macro shots show exactly how it works. Have you ever thought about taking the blue-shift out of your macros?. Like the picture below.

Regards,
Gerald

BTW: I like your web-site although it's a little difficult for me to read italian.

Gerald, it has been a pleasure for me, believe. I'm sorry that, being in Italian, the audience is quite smaller that with English, but a translation is quite time-consuming. I'll have to consider the thing, anyhow (plese no babelfish around ...). As far as the blue, you're absolutely right. I use Picasa (thanks Dave ...) so, if I remember, I can take care. Of course problem is just in macros, because I use daylight for pictures, not having room on my crammed table even for lightining equipment. Thanks again, Gerald
Warmest regards
Mario