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Explanation of Terms Used in Connection With the Detached Lever Escapement

From The American Horologist magazine, June 1937

Explanation of Terms Used in Connection With the Detached Lever Escapement
By W. H. SAMELIUS

Club - One of the teeth of a club wheel.

Club Wheel - An escape wheel with impulse planes on the ends of its teeth.

Dart (guard pin) - A pin or finger in the fork which engages with the edge of the roller, to prevent the accidental unlocking of the escapement.

Draft - The tendency of the escapement to resist unlocking, as shown by the return of the fork to the banking whenever it is moved away except by the balance. Draft is produced by inclining backwardly (that is, in the direction the acting teeth of the wheel are traveling) the locking faces of the pallet stones.

Drop - The space between a tooth of the escape wheel and the pallet from which it has just escaped.

Escapement, double roller - One in which accidental unlocking is prevented by the dart coming in contact with a separate roller called the safety roller of smaller diameter than the table roller which carries the jewel pin.

Escapement, single roller - One in which accidental unlocking is prevented by the dart (or guard pin) coming in contact with the edge of the same roller that carries the jewel pin.

Fork Hollow - The two curves that extend outwardly from the corners of the fork slot. In double roller escapements these are a necessary part of the safety action and prevent the unlocking of the escapement after the dart has entered the passing hollow of the roller.

Fork Slot - The rectangular notch in the end of the fork which engages with the jewel pin to unlock the escapement and give impulse to the balance.

Heel - The locking corner of the club escape wheel tooth.

Impulse - (The same as "Lift").

Impulse Planes - (The same as "Lifting Planes").

Lift - The angle through which the pallet and fork move while propelling the balance.

Lifting Planes - Those surfaces on the pallet stones and wheel teeth, which by sliding past one another propel the balance.

Lock - The distance from the locking corner of the pallet stone to the locking corner of the wheel tooth at the instant when the two come in contact.

Pallet - Strictly speaking, one of the two jewels (or "stones") that engage with the teeth of the escape wheel. It is also applied to the metal frame in which the pallets are fastened, and to the pallets and frame combined.

Pallet, Circular - A pallet the centers of whose lifting planes are equally distant from the pallet arbor.

Pallet, Equidistant Locking - One in which the locking faces are equally distant from the pallet arbor.

Pallet, Discharging - (Also called "L" stone and "Let-off" stone.)-The last of the two pallets to engage with a given tooth of the escape wheel.

Pallet, Receiving-(Also called "R" stone.) - The first of the two pallets with which a tooth of the escape wheel comes into engagement.

Pallet Stones - Effect of Moving in the Pallet Frame:
Drawing out the "R" stone increases the drop on the inside and increases the draft on the "L" stone.
Drawing out the "L" stone increases the drop on the outside and decreases the draft on the "R" stone.
Drawing out either stone increases the lock on both stones.
Drawing out the "R" stone and pushing in the "L" stone increases the draft on both stones.
Reverse movement of the stones produces contrary results.

Passing Hollow - The crescent-shaped notch in the edge of the roller, which permits the dart (or guard pin) to pass from one side of the roller to the other.

Rake - This refers to the front side of the escape wheel tooth extending from the locking corner down to the rim of the wheel. The teeth are said to "have rake" because they lean forward. The purpose of rake is to prevent the locking side of the pallet stone coming in contact with any part of the wheel tooth except the locking corner or heel.

Roller, Safety - The small roller that acts in connection with the dart to prevent the accidental unlocking of the escapement. The relation of this roller to the table roller must be such that in looking through its passing hollow at the end of the jewel pin, the two corners of the hollow shall appear to be equally distant from the sides of the pin.

Roller, Table - The larger roller which carries the jewel pin.

Slide - The distance that the pallet stone travels beyond the lock.

Toe - That part of the tooth of a club escape wheel which leaves the stone last.  The wheel travels from heel to toe.


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