An Analysis of the Lever Escapement Informative Summary

Overview:

This 1910 lecture by H. R. Playtner, delivered to the Canadian Watchmakers’ and Retail Jewelers’ Association, offers a detailed analysis of the lever escapement. Playtner begins by explaining the metric system of measurement and its significance in horology, then dives into the lever escapement’s history, tracing its evolution from Graham’s dead-beat escapement for clocks. He emphasizes the importance of precision and proper proportions in creating a high-performing escapement.

The bulk of the lecture focuses on examining the various aspects of the lever escapement, including the pallets, the lock, the run, the lift, and the center distance. Playtner explores the advantages and disadvantages of different forms of pallets (equidistant vs. circular) and teeth (ratchet vs. club) in detail. He also delves into the mechanics of the fork and roller action, including the unlocking, impulse, and safety actions.

Key Findings:

Circular pallets are better suited for general purpose watches than equidistant pallets. While equidistant pallets offer less unlocking resistance, circular pallets offer a more favorable lifting action and are less prone to certain defects.
A narrow pallet paired with a wide tooth offers superior performance compared to a wide pallet and a narrow tooth. This is due to the lesser frictional forces involved and the more efficient distribution of the lifting angle.
The fork and roller action can be divided into three distinct actions: unlocking, impulse, and safety. The ideal proportions between the fork and impulse angles are crucial for optimal performance and are influenced by the type of roller used.
A double roller escapement is preferable to a single roller escapement, as it provides greater safety and stability. By separating the impulse and safety actions, the escapement can function more reliably, especially in watches with finer proportions.

Learning:

The reader will gain a thorough understanding of the lever escapement, its history, and its various components.
- Pallets: Learn about the different types of pallets, their advantages and disadvantages, and how to determine the correct angles for each.
- Teeth: Understand the differences between ratchet and club teeth and their respective strengths and weaknesses.
- Center distance: Learn the importance of proper center distance for optimal performance and how it impacts the unlocking resistance and impulse transmission.
- Fork and roller action: Gain a detailed understanding of the unlocking, impulse, and safety actions, and how they interact to control the balance.
- Savage pin roller escapement: Discover this unique variation on the lever escapement that combines the benefits of both wide and narrow ruby pins.
The reader will learn about the importance of precision and proper proportions in horology.
- Playtner stresses the need for accurate measurements and careful consideration of angles, lifting angles, locking angles, and the widths of pallets and teeth.
- He emphasizes the importance of balancing the conflicting needs of the unlocking and impulse actions to optimize overall performance.

Historical Context:

This lecture was delivered in 1910, a time of significant advancement in horology. The lever escapement was well established as the preferred escapement for general-purpose watches, and horologists were continually seeking ways to improve its precision and reliability. The development of the Savage pin roller escapement, mentioned by Playtner, is a testament to this ongoing pursuit of excellence in watchmaking.

Facts:

The lever escapement is derived from Graham’s dead-beat escapement for clocks. The lever escapement was adapted for use in watches around 1750.
The lever escapement is the best form of escapement for a general-purpose watch. It offers a good balance of accuracy and reliability.
Thomas Mudge was the first horologist to successfully apply the detached lever escapement to watches. This innovation greatly improved the accuracy of watches.
The number of teeth in the escape wheel is not fixed in a lever escapement. While 15 teeth are common, other numbers are possible.
The pallet embracing three teeth is sound and practical. It offers several geometrical and mechanical advantages.
The equidistant pallet is sometimes called the tangential escapement. This is because the unlocking takes place on the intersection of tangents to the primitive circle.
The circular pallet is sometimes called “the pallet with equal lifts.” This is because the lifting arms on both pallets are of equal length.
The drop should be as small as possible. Excessive drop wastes power and contributes to irregularity.
The draw angle is necessary to draw the fork back against the bankings. It is measured from the locking edges of the pallets.
The lock should be as small as possible. A deeper lock increases the unlocking resistance.
The run or slide should also be as small as possible. A larger run increases the angular connection of the balance with the escapement.
The lift is composed of the actual lift on the teeth and pallets, the lock, and the run. The smaller the lifting angle, the more energetic the movement.
A narrow pallet requires a wide tooth, and a wide pallet requires a narrow or thin tooth wheel. The relationship between pallet and tooth width is crucial for efficient lifting.
The loss of lift is greater in the equidistant pallet than in the circular pallet. This is due to the difference in the paths of the discharging edges and the deviation of the tangents from the circle.
The lifting angle on the tooth must be less in proportion to its width than it is on the pallet. This is essential for a smooth and efficient lifting action.
The ratchet wheel offers advantages over the club tooth wheel. It has a constant lever length, less drop and lock, and is better suited to a wide pallet.
The center distance of wheel and pallets should be such that the direction of pressure of the wheel teeth is through the pallet center. This is achieved by drawing tangents to the primitive circle.
It is impossible to plant pallets on the tangents in very small escapements. The pallet arbor would be too small for proper strength.
A larger roller is required for a smaller impulse angle. This is because the ruby pin must be placed further from the center.
A round ruby pin should never be used. It violates the law of the parallelogram of forces and increases friction during unlocking and impulse.

Statistics:

There are 393708⁄10000 inches in a meter. This conversion factor is essential for understanding the metric system used in horology.
There are 25.4 millimeters in an inch. This conversion factor is essential for understanding the metric system used in horology.
The side shake for a balance pivot is .01 mm. This represents the amount of lateral movement allowed for the pivot.
The thickness for the spring detent of a pocket chronometer is about ⅓ the thickness of a human hair. This illustrates the precision required in watchmaking.
Every circle contains 360 degrees. This fundamental fact is crucial for understanding angles and their measurements.
A degree on the earth’s circumference measures 60 geographical miles. This demonstrates the scale and relative value of a degree depending on the size of the circle.
Authorities on escapements allow 1½° of drop for the club tooth and 2° for the ratchet tooth. This illustrates the typical drop angles allowed in escapements.
A total lock of 1¾° is recommended for the lever escapement. This includes both the lock and the run.
A lifting angle of 8½° is advisable for the lever escapement. This ensures a free vibration of the balance and an energetic movement.
A proportion of 3 to 1 for the fork and impulse angles is recommended for a single roller escapement. This balances the needs of the unlocking and impulse actions.
The width of the ruby pin is influenced by the freedom required in the slot. The wider the ruby pin, the greater the impulse radius.
A width of ruby pin equal to half the angular motion of the fork is recommended. This balances the needs of the unlocking and impulse actions.
A 12° pallet angle and a proportion of 3 to 1 for the impulse and pallet angles are recommended for the Savage pin roller escapement. This ensures the delicate action of this escapement.
The freedom between the guard point and the roller should be 1¼°. This ensures that the escapement remains locked even when the guard point is pressed against the roller.
The angle of opening for the crescent in the double roller escapement is greater than in the single roller escapement. This is because the safety roller is closer to the balance center.
The length of the horn should be such that the end points at least to the center of the ruby pin when the edge of the crescent passes the guard point. This ensures the safety of the ruby pin.
The space between the end of the horn and the ruby pin should be 1½°. This provides sufficient clearance to avoid collisions.
The radius of the safety roller should be 4⁄7 of the theoretical impulse radius. This proportion ensures a balance between the safety action and the impulse action.
The acting length of the fork is equal to the center distance of the escape wheel and pallets. This ensures a fork of a fair length.
The width of the slot in the fork is 5⅛°. This provides sufficient space for the ruby pin to move freely.

Terms:

Millimeter (mm): A unit of measurement in the metric system, equal to 1/1000 of a meter.
Degree (°): A unit of angular measurement, equal to 1/360 of a circle.
Drop: The amount of freedom allowed for the action of pallets and wheel.
Primitive diameter: The diameter of the escape wheel measured across the locking corners of the teeth.
Lock: The depth of locking, measured from the locking corner of the pallet at the moment the drop has occurred.
Run: The amount of angular motion of pallets and fork to the bankings after the drop has taken place.
Total lock: The sum of the lock and the run.
Tangent: A line that touches a curve but does not intersect it.
Impulse angle: The angular connection of the impulse pin with the lever fork.
Impulse radius: The distance from the face of the impulse jewel to the center of motion in the balance staff.

Examples:

The example of an escape wheel with 16 teeth in a watch beating 300 times per minute illustrates how to calculate the appropriate number of teeth for the 4th wheel and escape pinion. This demonstrates the importance of gear ratios in watchmaking.
The description of the equidistant and circular pallets provides clear visual examples of their different forms and their respective strengths and weaknesses. These illustrations help the reader visualize the differences in unlocking resistance and lifting leverage.
The use of diagrams to show the lift angles on the teeth and pallets helps the reader understand the distribution of power and the importance of proper proportions. This visual representation makes the complex mechanics easier to grasp.
The example of the Savage pin roller escapement demonstrates a unique and innovative approach to combining the advantages of wide and narrow ruby pins. This illustrates the ongoing development of the lever escapement to improve its performance.
The use of the drawing board and tools to create the detailed drafts of the lever escapement provides a practical example of how horological principles are applied in practice. This demonstrates the meticulousness required in watchmaking.
The detailed explanations of how to measure the draw angle in different positions of the fork and pallets illustrate the importance of accurate measurement in watchmaking. This emphasizes the need for precision in all aspects of escapement design.
The example of how to determine the loss of lift on the engaging and disengaging pallets provides a practical application of the principles discussed in the lecture. This illustrates how theoretical knowledge can be applied to practical situations.
The instructions for delineating the fork and roller action in different positions demonstrate the flexibility of the lever escapement design. This shows how the escapement can be adapted to different watch designs.
The example of how to measure the correctness of the drawing using the lock and lift angles provides a practical method for verifying the accuracy of the design. This demonstrates the importance of checking for consistency and accuracy in horological drawings.
The description of the escapement model created by Playtner provides a concrete example of how horological principles can be implemented in a physical model. This illustrates the importance of hands-on experimentation in understanding watchmaking.

Conclusion:

This 1910 lecture by H. R. Playtner provides a thorough and insightful analysis of the lever escapement, a crucial component in watchmaking. Playtner masterfully deconstructs the escapement’s mechanics, exploring the advantages and disadvantages of different forms of pallets and teeth, the importance of precise angles and proportions, and the intricacies of the fork and roller action. He offers valuable insights into the ongoing development of the lever escapement and emphasizes the importance of balancing conflicting needs to achieve optimal performance. By understanding the principles outlined in this lecture, watchmakers can gain a deeper understanding of the lever escapement and create more accurate and reliable timepieces.

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