CLOCK AND WATCH ESCAPEMENT MECHANICS Mark V. Section 1: Clock Escapements. 1: Efficiency and Power Losses. Page 4 2: Drawing an Escape Wheel.
5 3: Drawing the Graham Pallets. 6 4: The Graham Explained. 8 5: The Importance of the Simulation. 11 6: The Recoil Escapements.
16 7: The Brocot Escapement. 18 8: The Pin Wheel Escapement. 19 9: Other Design Considerations. 20 10: The Graham Reconsidered.
22 11: Efficiency in Numbers. 23 The first nine chapters are explained without math. These chapters are less complicated, and they introduce the reader to the logic behind the drawing techniques, so as to serve the needs of those who want to learn about escapements but would not be drawing them on their own computers. The tenth chapter explains the math behind the previous chapters.
This way the reader has the option whether or not to become involved with the math. References: Britten's Watch & Clock Maker's Handbook, Dictionary and Guide (1978 Edition). Donald de Carle: Watch and Clock Encyclopedia (1977 Edition). Fried: The Watch Escapement (1974 Edition).
View animations of the escapements in this book on my website at http://www.com/mvhw/ 1 Section 2: Watch Escapements. 12: Drawing the Club-Tooth Escape Wheel. Page 41 13: Drawing the Pallets. 44 14: Changing the Design.
50 15: Improving the Design. 53 16: The English Lever. 57 17: The Pin Pallet Escapement. 60 18: The Cylinder Escapement.
61 19: The Duplex Escapement. 63 20: The Chronometer Escapement. 67 21: Daniel's Independent Double-Wheel Escapement. 72 22: The Double-Roller.
79 Chapters 12 to 18 are similarly presented in order to introduce the reader to the logic behind the drawings, though these drawings are more involved and require some understanding of watch theory, such as lock, drop, draw, and impulse. Chapter 19 and beyond become more involved with the math that is required to create the drawings. The reader who does not want to become involved with the math could benefit from the logic of the latter chapters by passing over the math. I would like to thank the following for their invaluable assistance and encour- agement: Daniel Henderson Cecil Mulholland Roy Hovey Steve Conover Nino Gonzales Harry and Sue Wysong 2 Introduction.
Graham escapement Discover how much more there is to know about escapements by creat- ing your own drawings. The purpose of this project is to introduce the reader, whether professional or hob- byist, to a hands-on method for draw- ing a mechanical clock or watch es- capement. While it is more obvious that a manufacturer needs to know how to design a pallet, the repairman could do a better repair with an im- proved understanding of design the- ory. The ability to draw an escape- ment enables one to experiment more easily with the effects of changing the variables and to compare different Strip-pallet recoil types of escapements, their similari- ties and differences.
The most important reason for careful attention to design is effi- ciency. The escapements most fre- quently encountered at the bench are the Recoil, the Graham (or dead-beat), and the Swiss Lever. These all have efficiencies below 50%. This means that more than half the power is lost in the escapement alone, after all the power losses in the gear train.
modern Swiss Lever These drawings are not dissimilar to what I have seen in escapement literature. They do not reveal the methods by which they were de- signed, why the lines and curves are positioned so. If these drawings ignite your curiosity, this project is for you. 3 1: Efficiency and Power Losses.
A clock is usually taken to the shop for repair because the clock fails to keep running. It runs for a while and stops because not enough power reaches the pendulum to keep it running. One way to get it running is to double the weight, but this causes enor- mous wear and consequent damage in the long run. The other way is to overhaul the clock.
The job of the repairman is to do whatever is necessary to minimize the power losses between the weight and the pendulum. The clock is cleaned. Pivots are polished. Worn bushings are replaced.
Adjustments are made to the escapement to improve its action. The clock is carefully lubricated. Other repairs are made as needed. These all have the ultimate goal of reducing power losses.
There are two kinds of power losses in a clock: frictional losses and losses caused by the action of the escapement (which result in additional frictional losses). Frictional losses are easily understood. The lubricant has failed, causing drag. The bushings are worn, so the gear and pinion teeth grind together.
The pivots are scored, causing frictional losses from rough surfaces. Dirt particles become imbedded in the worn bushing, causing binding of the pivot, and so on. Power losses caused by the action of the escapement are less obvious. The following reasons are explained in detail in subsequent chapters.
If the escape wheel rotates clock- wise, the force it exerts on the pallet would be in a different direction to that of the pallet's movement. The greater the angle between the two directions, the greater the loss of power as it is transferred from the escape wheel to the pallet. Consider that the pallets rotate clockwise as the escape tooth pushes on the entry pallet, and counterclockwise as the tooth pushes on the exit pallet, yet the escape wheel continues to rotate in the same clockwise direction. As the escape tooth pushes on the pallet, the tooth exerts a force in the same direction as its direction of travel at that point.
If the point of contact on the pallet were at 90º to this direction, such as on the locking face of the Graham pallet, the escape tooth would not move forwards and no power would be transferred to the pallet. If the point of contact were in the same direction as the escape tooth, so that the pallet's impulse face were parallel to the path of the tooth, the tooth would pass by freely and provide no impulse to the pallet. No power is transferred to the pallet when the angle is 90º or 0º. An angle in between is needed: the angle that maximizes the power transfer.
Find what direction the escape tooth is moving in as it passes over the pallet, and the direction of the pallet. Then determine the direction in which the pallet should receive power from the tooth. The di- rection should be half way between those of the tooth and of the pallet. For maximum efficiency, the pallet's impulse face needs to be at right angles (90º) to this direction.
If the angle between the directions of the tooth and of the pallet were 90º, the maxi- mum achievable efficiency would be only 50%. This is achieved when the impulse face's 4 angle is at 45º to the direction of the tooth's travel. If the impulse face's angle were 25º, the efficiency would be merely 38%. That is a 24% power loss caused by improper de- sign.
If the repairman could see this, he could adjust the impulse face's angle more closely to what it should be, and maximize the pallet's efficiency, given the original design he has to work with. Ideally, the impulse face's angle should be at 90º to the angle half way between the directions of the tooth and of the pallet. You may not find this easy to understand: power losses by escapement design are less obvious. This will become clearer in the next chapters, as we draw the Graham escapement.
It should, however, have become clear to you how important the design of the escapement is. I have seen clocks in which one pallet received a negligible impulse from the escape wheel, so the maximum achievable efficiency was only 25%. Why would they would not keep running? 2: Drawing an Escape Wheel. I am currently using an IBM with Windows and a drawing program called Key- Draw.
If you have AutoCAD, you are well equipped. The most important features you need are the ability to draw lines and circles on a grid, and the ability to rotate the lines by angles that you determine. You may have a different method. This is just one way to do it.
First, draw a large circle. A diameter of 6 inches worked well for me. Draw another circle of 4.5 inch diameter and center it inside the first. Draw a horizontal line across this circle, bisecting it.
Draw a tooth on one side until you are satisfied: I chose a line at 15º and another at 25º from horizontal, positioned to fit, and with a small gap to allow for tooth thickness. Duplicate, rotate, and place a tooth on the other side. Your drawing should look like this: Move the inner circle outside. Group the outer circle with the line and the two teeth, duplicate and rotate by 12º.
Duplicate the new group and rotate it by 12º again. Repeat this until you have thirty teeth. Ungroup all the elements and remove the outer circles, one at a time, until only one is left. Place the inner circle in its original position, and group all the teeth and circles.
The reason for placing a tooth in a circle before rotating is because the circle makes the tooth rotate about the center of the circle, in order to achieve the desired result. 5 Rotate the groups by 12º at a time because there are 360º in a full circle, so if you want a 30 tooth circle: 360 / 30 = 12º. If you want a 48 tooth circle, divide 360 by 48 to get 7. Thus escape wheels with different numbers of teeth could easily be made.
Escape wheels with the teeth pointing in the other direction could be made by flipping the image, or with teeth of different shapes, such as the club-tooth escape wheel in Swiss watches. 3: Drawing the Graham Pallets. Over the escape wheel, draw two radius lines at 90º to one another. Draw two more lines at 90º to the radius lines and place them at the edge of the circle.
The point where these new lines inter- sect is the center of the pallet cir- cle, the radius of which should measure three inches. Draw the pallet circle about this point. You now have four radius lines. Draw two more radius lines next to each one, positioned at 3º on either side of each.
I chose to extend all the radius lines: Since the escape wheel rotates clockwise, the entry pallet is on the left side of this drawing. Draw a horizontal line between the three lines. The exit pallet is on the right side: draw a vertical line between the three lines there. 6 It is important to draw the locking faces, which will consist of curves drawn over circles, such as to preserve the dead-beat nature of the design.
Draw two more pallet circles with diameters of 5. Once these lines have been completed, the rest of the pallet could be drawn any way you wish. I drew the this one by drawing a hori- zontal line across the pallet circle, then rotating it by 24º, duplicating it and placing one line 0.25 inches above the center line and the other 0. I grouped these two lines, duplicated them, flipped them horizontally, and placed one pair on the other side.
Remove the excess lines to get the result. This is the ideal Graham design as its angles maximize the power transferred from the escape wheel to the pallets. 7 4: The Graham Explained. As the escape wheel rotates, it exerts a force upon anything it encounters in its path.
The direction of this force depends on what point on the escape wheel the pallet is located, as shown here: the arrows show the different directions of force for three points on the escape wheel.