Mechanics of Micrometers.

Use And Care Of Handtools And Measuring Tools
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smallest models have a 1/4 inch screw, the average have a 1/2 inch screw,

and the largest inside micrometers have only a 1 inch screw.

c. Mechanics of Micrometers.

(1) Design. The micrometer makes use of the relation of the circular

movement of a screw to its axial movement. The amount of axial movement of

a screw per revolution depends on the thread, and is known as the lead. If

a circular nut on a screw has its circumference divided into 25 equal

spaces, and if the nut advances axially 1/40 inch for each revolution, then

if it is turned one division, or 1/25 of a revolution, it will move axially

1/25 x 1/40, or 1/1000 of an inch. In the micrometer, the nut is stationary

and the screw moves forward axially a distance proportional to the amount it

is turned. The screw on a micrometer has 40 threads to the inch, and the

thimble has its circumference divided into 25 parts, so 1 division on the

thimble represents an advancement of 1/1000 of an inch axially.

(2) Construction.

(a) The steel frame is U-shaped, one end of which holds the

stationary anvil. The stationary anvil is a hardened button either pressed

or screwed into the frame.

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