Long second hand to match long minute hand

Posted: Mon Aug 17, 2009 11:02 pm     Post subject: Long second hand to match long minute hand

There are seven inch minute hands (and longer) available for the high torque atomic clock movments, but I have only seen short second hands. Should the second hands not be nearly the same length as the minute hand? Otherwise, the comparatively short second hand would look rather anemic.

Posted: Tue Aug 18, 2009 2:29 pm     Post subject:

You have touched upon an apparent weakness with our product offerings. It is true: While we have minute hand lengths beyond 7", we do not carry a second sweep which would exceed 5".

I am curious if this possibly has something to do with the amount of power that is delivered to the hour and minute hands. With a high torque movement, most of the power is required for those specific hands to ensure that the movement can pull each hand up from the 6 to 12 positions. Longer hour and minute hands are even counter-balanced to help ensure that there are no problems. An additional second hand of equal length to the minute hand may steal power from the main hands (resulting in possible time loss).

If a longer second hand is available for these movements, it would require some test time to ensure that a large second hand would not inhibit the main hands from proper timekeeping.

Posted: Tue Aug 18, 2009 5:56 pm     Post subject: Angular momentum

Chis, you spoke of the minute hand stealing power from the main hands. The stepper motor in these movements primarily drives the second hand. The minute and hour hands are geared from the second hand. I don't think the minute and hour hands pose a significant problem if they are ballanced, but the second hand is another matter. Since there is an impulse every second, the mass of the second hand is what drives the stepper motor requirement. The angular momentum must go from zero to maximum every second (for each 6 degrees of movement).
It would be pointless to go into a discussion of moment of interia in a forum like this, but suffice it to say that a high torque movment, if it is properly designed, should handle a long second hand, particularly when the second hand is such an important part of synchronizing the "atomic clock" movement.
I agree with your conclusion that there is a weakness in your product offering. I have avoided purchasing these movements since they were first offered because of this weekness. While it isn't impossible to fabricate a second hand, it would be far easier to purchase one. Feel free to pass the observation on to your marketing people.

Posted: Wed Aug 19, 2009 2:06 pm     Post subject:

I am, by no means, an expert of quartz movements and gearing, but I would be more than happy to pass along the request for longer second hand sweeps (which could be used with high torque movements).