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US Patent: 202,866
Micrometer Gage
Patentee:
George M. Pratt - Middletown, CT

USPTO Classifications:
33/828

Tool Categories:
metalworking tools : machinist tools : measuring tools : micrometers

Assignees:
Victor Sewing Machine Co. - Middletown, CT

Manufacturer:
Brown & Sharpe Mfg. Co. - Providence, RI
Victor Sewing Machine Co. - Middletown, CT

Witnesses:
James L. Norris
James A. Rutherford

Patent Dates:
Applied: Mar. 23, 1878
Granted: Apr. 23, 1878

Patent Pictures: [ 1 | 2 | 3 | 4 ]
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Martin J. Donnelly Antique Tools
"Vintage Machinery" entry for Brown & Sharpe Mfg. Co.
American Precision Museum
Description:
This invention relates to that class of micrometer gages having horseshoe shaped frames, in which the object to be measured is clamped between a suitable abutment and the tip of a micrometer-screw. In order that the measurement by such an instrument shall be absolutely correct, it is necessary that the surfaces of said abutment and screw shall be perfectly smooth, and they should, therefore, be made as hard as possible, to resist abrasion and wear. In hardening these surfaces, the ordinary methods of tempering have been employed, the screw being completely formed and adjusted while the metal of which it was composed was soft, and afterward tempered. In thus tempering the screw after its complete formation, it has been found that its adjustment is always more or less impaired, as the heat necessary in the process of tempering expands the metal, a portion of the expansion being permanent, and the contraction, on cooling, unequal so that, though a micrometer-screw should be perfectly accurate before being tempered, it would often, after tempering, be found so altered as to materially affect its accuracy in the minute measurements for which such instruments are employed, and is then worthless for its intended purpose. Besides, when the screw is first perfectly accurate, if its tip becomes much worn, a new adjustment or the substitution of a new screw is necessary in either event involving more or less expense. The bar forming the horseshoe or U shaped frame of such an instrument has heretofore been formed of uniform width and thickness throughout its length; and, in order to give it sufficient rigidity to prevent springing, this frame has been of inconvenient weight and bulk. To obviate the necessity for heating the screws for tempering, to provide for their easy repair, thus reducing the expense, while preserving the accuracy of micrometer-gages, and also to render the frame of such an instrument strong, light, and of elegant shape, is the object of my invention; and it consists, first, in a micrometer-gage screw, having a socket formed in its end, and provided with a separate tip of tempered steel or similar hard material, whereby the necessity for heating the screw, in order to temper the tip, is obviated, and said screw is rendered easy to repair by the simple replacement of a worn tip by a new one, properly hardened and adjusted; second, in forming a micrometer-gage frame of an approximately crescent shape, or semicircular and tapering from its middle portion to its ends, in which the screw-bearings are located.

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