Page:Popular Science Monthly Volume 89.djvu/30

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��Popular Science Monthly

��STANDARD

��ADJUSTMENT SCALt

��MEASURING , POINT

���If a machine part is too small by one twentieth the width of a hair, this measur- ing scale can detect it

A Measuring Machine More Sensitive Than a Human Being

THE average person has little con- ception of the accuracy with which it is necessary to work on some classes of machinery. Ball-bearing parts, for instance, are produced in large quanti- ties, yet in some cases the limit of error is placed at one tenth of one thousandth of an inch or about one twentieth the thickness of a human hair. Special measuring appliances are needed to make these fine measurements in a commercial way because hundreds ot du|)Iicate parts must be gaged per day. 'l"he human sense of touch is coarse in comparison.

The multiphing indicator illustrated is a very satisfactory device for measur- ing parts that must be accurately gaged without loss of time. The machine consists of a substantial Ijase-plate witii an accurately' ground, hardened steel facing and an integral stanilard carrying a measuring appliance. The dial-intlica- tor reads in thousandths of an inch, eac-h graduation representing a one- thousandth inch movement of the in- dicator stem.

Thi- work to be measured is placed under the measuring point on the

��multipKing lever. As this is \-ery near the fulcrum, a relatively slight motit)n will be changed to one of ten times that magnitude at the dial-indicator. If the work is but one thousandth inch larger or smaller than the standard, the pointer of the indicator will mo\e over ten graduations on the dial. An error of one tenth of a thousandth will move the pointer one graduation. The measur- ing arm may be mo\ed up or down to accommodate work of varying diameter, and when gaging duplicate parts, it is set by a standard master-disk of the correct dimensions. Any de\Mation can be easily detected by a comparatively inexperienced of)erator.

��Lighting the Inside of an Oven

Ali.\KER'S o\en, illuminated on the inside, is a great advantage since otherwise the contents cannot be closelj' inspected, unless withdrawn from the oven. An arrangement, suitable for electric or gas lighting, is shown in the illustration. The door is hinged to the frame b>- means of pins. One pin is provided with a counterweight to facili- tate the action of the door in opening and closing. The other pin has a crank- arm. On an extension on the door is mounted a knife-switch, with two short fingers to engage with the crank-arm. The opening of the door establishes an electrical connection with a lamp moun- ted in a casing near the door. If gas is used, the crank-arm engages with the shank of a vaKe which regulates the How of gas to till' burner in I he casing.

���The act of opening the oven door completes an elcctricnl circuit for lilthting the inside o: the oven. A similar arrangement can be used for gas

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