USE/CARE OF HANDTOOLS & MEASURING TOOLS - OD1621 - LESSON 3/TASK 1
smallest models have a 1/4 inch screw, the average have a 1/2 inch screw,
(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.
(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.