Classic Escapement - Graham (Modified)

Last crawled date: 1 year, 11 months ago

This is the continuation of my former project Classic Escapement - Graham (Ideal).
Based on the book CLOCK AND WATCH ESCAPEMENT MECHANICS by Mark V. Headrick (Copyright 1997) as a fine source, I try to present rigorously the essence of escapement design. The book is public and you can find it here: http://www.nawcc-index.net/Articles/Headrick-EscMechanics.pdf, so you can read and compare (with the book) everything I present here. I recommend you to download the book in order to use it when your computer is offline.

All parts, assemblies and simulation/animation are made with Inventor 2014, so some specific references are bonded to this software.
This is the presentation of the Modified Graham escapement explained in the book between page 11 („5: The Importance of the Simulation”) and page 15.
Firstly you have to look to the picture showing the Inventor sketch „Wheel - Palette modified.jpg”. The difference from the Ideal escapement (see https://grabcad.com/library/classic-escapement-graham-ideal-1) is that the left and right ends of the palette are thinned, so they are now able to enter between the teeth of the wheel. You notice the angle of 2° on each side of the palette, accordingly with the explanations in the book at the page 11.

Watching the Video you see immediately the movement of the palette, due to the pendulum which is jointly to it. Now the rotation of the wheel is permanent, step by step. Why? Because of the imposed motion, this is why. Again, when the mechanism is presented from the back you understand that a thread and a weight must be spooled on the reel to produce the motion. They are not present because threads/ropes are not allowed in Dynamic Simulation in Inventor. Instead, a torque (of only 6 N·mm) is applied to the reel.
The wheel feeds the movement of the pendulum so the pendulum is permanently maintained swinging. This is made because of the perpendicular placement of the red faces of the palette shown in the picture „Contact and impulse faces.jpg”. This is really important, and the book emphasis the aspect. A small part of the wheel energy is transferred to the pendulum each time the palette sweep the teeth with these faces. You understand that the potential energy of the virtual weight which hangs on the reel is consumed on this way almost strictly to feed the pendulum movement. Longer the contact face - greater useful energy is transferred from the wheel. This is why we carefully thin the arms of the palette, and that two degrees are awarded sparingly.
Included are the files „Output Grapher (10s).jpg” and „Output Grapher (60s).jpg” where you can see the graphs of movement of the wheel and the palette. The points considered are the same A and B as in the previous project (Ideal). When the time is longer (60s) you can see an increase of the amplitude of palette oscillation. This can be adjusted by changing the length of the pendulum rod.

Enjoy!