16: The English Lever

This escapement has several disadvantages. The escape wheel's teeth are pointed, so they lack the strength of the club-tooth design. The escape wheel's teeth do not have impulse faces of their own, so the lock must be created by changing the design of the pallets. This results in the pallets having impulse faces with angles other than the optimal angle, so the design is less efficient.

The escape tooth is simple. The locking face appears to lean forwards by 24º. There is an angle of 12º between the front and the back of the tooth, and there is a small gap to create some thickness.

As in the Swiss Lever, there is 30º between the vertical line (1) and the escape circle radius lines, (2) and (3), which are used to design the pallets. Rotate line (2) by 90º to get line (4). Rotate line (3) by 90º to get line (5). Place the pallet circle such that its center lies on the point where lines (4) and (5) intersect.

The 15 tooth escape wheel rotates by 12º per beat, so make the pallet occupy a span of 10º, in order to allow 2º for drop.

To draw the impulse face lines, it is necessary to determine their positions. Rotate line (4) by 2º (for lock) counterclockwise to get line (10). Then rotate line (10) by 8º counterclockwise to get line (11). Rotate line (5) by 8º counterclockwise to get line (12), and by 2º more to get line (13). Draw a line from the point where lines (6) and (10) intersect to where lines (7) and (11) intersect: this will be the entry pallet's impulse face. Draw a second line from the point where lines (8) and (12) intersect to where lines (5) and (9) intersect: this will be the exit pallet's impulse face.

Rotate line (6) clockwise by 15º to get line (14), which will be the entry pallet's locking face with a draw angle of 15º. Duplicate line (14) and place it on the point where lines (7) and (11) intersect. Repeat this procedure for the exit pallet: rotate line (8) clockwise by 15º to get line (16). Duplicate line (16) and place it on the point where lines (5) and (9) intersect. Finish the drawing as you wish.

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