Recent content by John MacArthur

  1. J

    Query pendulum amplitude

    Upon looking at various definitions, I see that many show the amplitude as being only half the swing. This may be related to electronic theory - it doesn't have much to do with the actual behavior of a pendulum except in mathematical analysis. Semantics and pendulum construction are quite...
  2. J

    Query pendulum amplitude

    Amplitude of the pendulum is the total swing angle from end to end, not from center. If this is a weight driven clock, it will likely lose a little amplitude when the weights are slightly below the level of the pendulum bob (i.e. where their cables are nearly the same length as the pendulum)...
  3. J

    Dividing Head for Mill

    I love my CNC. It's a better hacksaw. The finish work, except in the case of gear teeth, is still all done by hand. Johnny
  4. J

    Dividing Head for Mill

    The Sherline rotary table indexer (CNC Rotary Table Indexer – Sherline Products) can be used on any manual mill. You index it with the controller and then cut the teeth manually the old way with the mill. It works best if you mount it on an angle plate. Johnny
  5. J

    Antique regulator clock

    Maybe show us a pic of the pendulum suspension and top block as well. In your pics there appears to be a cross-wise mark on the end - possibly remnants of a cross hole that had been cut off? What brand of clock is it? Johnny
  6. J

    Carriage clock

    It's not a carriage clock and the whole strike control mechanism is missing. Johnny
  7. J


    Pepi - I like Rawlings, Goodrich, and Gazely myself. Johnny
  8. J

    Help Fly Cutter to Cut a 56 tooth Wheel

    Not to argue with Jerry, but I too run my shopmade fly cutters a lot faster than 500 rpm. From an experimental viewpoint why not try both? Obviously, to some degree it would depend on the working diameter of the cutter and if it had been properly hardened and tempered (which is where this...
  9. J

    Help Fly Cutter to Cut a 56 tooth Wheel

    Try tempering the cutter a bit higher - 450-475 F, or 235-250 C. This should be a dark straw or light brown color. Also, 400 rpm is way slow, it should be something like 10 times that. Good luck Johnny
  10. J

    Tempering Hardened W1?

    Did it turn blue? I think 485F is not hot enough for W1, you'll need more like 575 to 600, and it'll still be pretty tough. It should turn dark blue. The second heat at the same temp won't change the hardness much, if at all. And depending in the size of the piece, you shouldn't need two...
  11. J

    Grasshopper clock

    Very nice Ernie! Johnny
  12. J


    As to the power of the escapement varying by an order of magnitude: Since the escape wheel is "geared up" by a factor (usually) of some 43k, the minute changes in lubricant viscosity make a large difference in rotating resistance, as many, many clockmakers have noted over the centuries. I am...
  13. J


    Pepi - what limits the amplitude is the combined angles of impulse added to the combined angles of lock. My early clocks had impulse angles of two degrees, and a little more than half a degree of lock. They take a fairly large swing. My more recent ones have 1.5 degrees of impulse and at most...
  14. J


    You might look into "Science of Clocks and Watches, Rawlings. His analysis is somewhat disputed, but he gets closer to what you are looking at than others. The best books on layout of Grahams are Gazely "Practical clock escapements" and Goodrich "The Modern Clock". From the looks of things...
  15. J

    How do I properly polish a verge??

    Yes Dan - I'm rotating the anchor (strictly speaking, a verge is something else) so that the inside and outside surfaces are true arcs centered on the pivot. In polishing like this you must keep the object moving or else you risk leaving grooves. In this case the tiny increments are adjusted by...

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Weekly News 7/7/19 by Tom McIntyre