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Lever escapement

Lever escapement The lever escapement is the escapement par excellence of luxury or standard watches, however small or large. It is robust, relatively easy to make and completely reliable. It also produces the highest timekeeping accuracy. A lever escapement consists of an escape wheel, mounted on the last wheel in the train of gears. A lever. One or more rollers fixed to the balance staff and engaged in its movements. The lever escapement is made of hardened steel in high-quality watches and of brass in standard or non-magnetic watches. The escape wheel has to be lightweight and, depending on its qualities, may be hollow on both sides or on one side only, flat, double bevelled, single bevelled. The lever's shape is vaguely reminiscent of a ship's anchor. The lever, depending on its quality, is made of hardened steel, polished or matt, or non-hardened and matt, non-hardened steel or brass. If made of hardened steel, it may be angled or non-angled. The lever carries two pallets. In superior quality watches, these pallets are made of red or colourless rubies or sapphires, or garnet in medium quality watches. The roller is either single or double. It is made of steel or brass. The roller carries a pin, which is still often referred to as an "ellipse", or impulse jewel, in watchmaking circles on account of its antique form. The roller pin is made of ruby, sapphire, garnet or even steel in standard quality watches. The "visible" pallet jewels of the lever escapement can be easily seen by looking into a watch from above when the pallets are locked perpendicularly in the plane of the lever. When these pallets are completely hidden by the metal holding them in place, the escapement is said to have "covered" pallets. The lever escapement works as follows: in the rest position (when the gears are at a standstill), a tooth of the escape wheel presses against one of the lever pallets. As the balance wheel turns, the roller pin, which is engaged in the movement, comes into contact with the entrance pallet, and makes it turn at a certain angle, thus releasing the wheel; this in turn is set in motion, and the same tooth, by activating the pallet, sends its impulse to the lever. The lever in turn sends an impulse to the balance via the roller pin. The balance continues to move while another tooth on the escape wheel comes to rest on the second pallet. The same operation is repeated in the opposite direction etc. The first pallet is called the entrance pallet and the other the exit pallet. The purpose of the small roller, dart and horns is to prevent unlocking which could accidentally happen as a result of shaking or when setting the time. The banking or unlocking pins are used to restrict the movement of the lever. The lever escapement achieves very precise timekeeping in a watch as it leaves the balance free to oscillate. All three parts of the escapement - the wheel, lever and roller - make up what is known in the jargon as the "assortment".