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US Patent: 211,975
Micrometer Screw Gage
George W. Dickinson - Ashtabula, OH

USPTO Classifications:

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


Not known to have been produced

L. A. Watson
E. W. Richards

Patent Dates:
Applied: Dec. 11, 1878
Granted: Feb. 04, 1879

Patent Pictures:
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The abandonment in the best workshops of haphazard fitting and the constantly increasing accuracy with which it becomes necessary to construct machinery render handy and reliable instruments for measuring minute linear magnitudes indispensable to machinists, compasses, calipers, and graduated rules being no longer sufficient for the refinement of modern workmanship. Compact and strong micrometer screw gages of various kinds have been devised to meet this want, but they have failed to satisfy it for various reasons. The simple pocket micrometer screw gage upon the general plan of that shown in the drawings is preferred for general use; but there is difficulty in bringing its gaging surfaces into certain contact with the opposite sides of an object to be measured without either compressing the object or flexing the frame of the gage by too great pressure of the screw, which can scarcely be avoided in the ordinary manipulation of- the instrument by the stiffened fingers and strong muscles of mechanics. To prevent such undue pressure the milled head for rotating the screw was pivoted to the end of the screw, and a spring friction brake or clutch interposed between1 them, so that the turning of the milled head should turn the screw with no greater force than was required to overcome the friction of the interposed spring clutch, the screw stopping whenever the resistance to its motion exceeded such friction, while the milled head might continue turning. This arrangement, while guarding against excessive pressure by the screw, created new difficulties by failing to make provision for varying resistance to the turning of the screw from grit, filings, and other factional matter, which inevitably gets upon the screw and nut in the pocket and on the work-bench; nor did it make any provision against change in the resistance of the friction-springs from loss of tension or from the polishing or the abrasion of the rubbing-surfaces. Another device to secure equal pressure of the gaging surfaces upon all objects under measurement is to make the micrometer-screw tubular, and to fit into it accurately a sliding rod and certain levers, springs, and graduated indexes. This device is known as the "contact-lever gage;" but, while delicate in its operation, and capable of measuring with great nicety, it has neither the strength, nor compactness, nor the convenience of application requisite for a bench and pocket tool in a machine shop. It is often desirable to apply the gage to an object to ascertain its thickness under circumstances where the scale cannot be seen, and to remove the gage for the purpose of reading the measurement. With the ordinary gage this is difficult, because in removing it from the object the friction against the flat end of the micrometer screw is apt to turn it, and so falsify the measurement or if the screw be made to fit tight enough in its nut to avoid this cause of error, the delicacy of the gage is so much impaired as to unfit it for nice measurement. My improvements, which are designed to remedy the aforesaid and other defects in gages, are shown in the drawings in connection with one of the common forms of the pocket and bench micrometer-gage.

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