A Treatise on Modern Horology in Theory and Practice
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1887 edition. Excerpt: ...perfectly made, was shown at the Exhibition of 1855 by a modest but very clever watchmaker, M. Sylvain Mairet of Locle. Escapement with Ratchet Teeth. 742.--In a small work on watchmaking we readj "Pointed teeth are best suited to the lever escapement because they traverse a longer impulse plane and therefore exert a greater force on the balance." This assertion is utterly gratuitous. For consider an impulse plane nod (fig. 49): the pointed tooth b will impel it backwards through the interval d h and in doing so will traverse the full extent, n o d, of the plane. Now assume half of the plane to be on the tooth and half on the pallet so that we have the two inclines n i and i d. The corner i of the tooth will traverse the incline i d, and the corner d of the pallet will be driven backwards over the plane n i. On the whole the displacement of the pallet will remain the same (A d), and it will be just as if a pointed tooth successively passed over the two planes n i andz d joined end to end, so that in fact their total length would be slightly in excess of that of the original plane nod. 743.--An escapement with pointed or ratchet teeth has the following objections and advantages: Both the pitch with the locking face and the drop are very nearly doubled; there is therefore an appreciable increase in the resistance opposed to unlocking, especially when the oil is at all thick. Out of the 10 through which the pallet moves, a greater proportion is expended in the unlocking (705). Lastly the fine pointed tooth must be made of brass, it is liable to wear and distortion and is ill-adapted for retaining oil, which must be applied in very small quantity. On the other hand its advantages consist in: (1) the pallets having double width so that a...
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