Daisy Wheel / Hour Hand
  • Is there any Way or View that better explains the function of the Daisy Wheel in regard to how the minute arbor turns the Hour hand. I guess I'm just having issue Visualizing it's function...
  • I'm glad I'm not alone! I couldn't work it out either so I went on a hunt and found a description at http://www.raynerd.co.uk/?p=1488

    Here is another video which shows a daisy wheel:


    I'm not sure what the stem is for as I got a bit lost in the description about that, so although I now see how the gearing works I still couldn't make one.

    Pete
  • The Daisy wheel is one of those things that has to be seen in action to be understood, like the grasshopper escapement.

    It was invented by the American clockmaker Aaron Dodd Crane (1804-1860) and is an absolutely ingenious way of reducing the 1 hour revolution of the minute hand to the 12 hour revolution of the hour hand.
    Normally this 1 to 12 reduction would need 2 pinions and 2 cogs if made with gears.

    It is basically a harmonic motion drive, the daisy wheel is oscillated by an eccentric fixed to the minute arbor, as the wheel oscillates it catches the pins on the pinwheel and advances it.

    The daisy wheel has one less petal than the amount of reduction, so as with the hour hand the reduction is 1 to 12 but the daisy wheel has only 11 petals.

    The holding rod attached to the daisy wheel bottom, prevents it just turning on the eccentric, depending upon design, it can either just hang down with a weight attached or, as with the Primus, held in such a way that it can still move up/down.

    Although I understand how it works, what amazes me is how anyone could come up with something so counter intuitive, absolute brilliance.

    The only drawback with the daisy wheel is it is no good for high load work, as it would just develop too much friction and start binding, but works fine with the hour hand as it only has a few grams.