Model: 049 ??? Ratchet Wheels (Boston) or Ratchet Pawls & Stops (Newark) ???
Ratchet mechanisms occur in a great variety of forms. A ratchet consists of a wheel with teeth called the ratchet wheel which receives periodic or intermittent motion from a swinging member called a ratch or pawl. Another pawl prevents backward motion, this is called a stop pawl. Model 1 shows three kinds of stop pawls, each form being necessary to perform its function under different conditions of space in mechanisms to which they are attached. A is the hook type and prevents backward motion by engaging with teeth. B is the straight type and acts as a barrier. Both of these have spring tensions to keep them in place. C is the gravity type, which is held in place by its weight below center. In Model 2, motion is transmitted to the ratchet wheel by the revolving pawl drive. The stop pawl is of the straight type.
[Virginia Downward & William M. Clark, 1930]

[Editor’s Note: Ratchet mechanisms are like diodes and digital devices in electronics; limiting motion in one direction and permitting only discrete motions. Franz Reuleaux was very much intrigued with ratchet mechanisms so much so that his collection as produced by Voigt in Berlin contained 26 ratchet models in the N series not to mention 12 models in the X series on escapements. He also called some ratchet mechanisms click wheels. Clark designed this model after Figures 75, 76 in Henry T Brown's 1868 catalog of mechanical movements. See also Clark model 50. FCM]

Francis Moon 2005-00-00

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