I saw this clock in a catalog last night:
I like 24-hour clocks; and I’m a computer geek, so I use 24-hour time for its unambiguity. And I like the visuals of this clock — but it’s functionally useless and/or made for idiots, as the 24-hour-ness of it is strictly cosmetic. It gives you no idea whatsoever whether it’s currently 07:00 or 19:00; it just has both numbers painted on, and the hour hand will point in the general direction of both.
How ’bout a clock with a face like this — numbers spiralling inward — and an hour hand that slides back and forth end to end across its axis as it turns, so that the end of the hour hand is always touching the marking for the correct hour? At 07:00, the hour hand is still slid most of the way to the outside of the clock and its end touches the 07; at 19:00, the hour hand has withdrawn further across the center of the clock and its end touches the 19.
Of course it’d need to be done with gears; I’m not talking about an LED or LCD clock.
Gears? We don’t need no stinking gears! There are plenty of other ways of doing it. You could use a fine resolution stepper motor to drive the hands (well, ok, so maybe you would need a gear to drive both the hour and minute hand, since I don’t know of any coaxial stepper motors, although it might be fun to design one).
As for the lengthening/shortening of the hour hand, there may be other options. What about using some of that Nitinol (Nickel Titanium shape memory alloy) to make the hour hand from:
http://en.wikipedia.org/wiki/Nitinol
And, then suppling heat to make it change shape from a long pointer to a short pointer. Bonus points for electromagnetically coupling energy from behind the clock face to the hour hand to supply the heat.
I’m sure there are many more ways, other than simple mechanics, to perform this.
Dave
You could have a spiral grove in the clock face. A sliding extension on the hour hand has a peg that tracks the groove. The tricky part is resetting the peg to the outer groove at the end of the day. I guess you could this with special mechanics that would force it to the outer groove. Interesting design problem.
Dave, those are definitely cool ideas! I’m kinda fascinated by the idea of doing it all mechanically, with gears or cams or grooves (good idea, JP!), though.
I wouldn’t choose the hard way if I were building something to mass-produce; but I’m fascinated by things with gears, from Isaac Youngs’ all-wooden Shaker clocks to the Clock of the Long Now to Curta calculators. So I’d love to see one of these done all with gears — and I think I’d like it even better with a geared mechanism between the shaft and the hand than by having the end of the hand ride in a groove, as good an idea as that is.
Just my $.02.
Easy. make two (or more) clocks that exchange in a cabinet. Real clock cabinets take up space.