A
Micrometer is basically a measuring instrument. A Micrometer is also known
by another name and that of Micrometer Screw Gauge. As compared to a
Calliper it provides a greater accuracy but measures a smaller range of
lengths.
With a Micrometer the thickness of blocks, depths of slots or
diameters(both I.D and O.D) of shafts can be easily measured along with
length roundness or bore. Mechanical micrometers in the form of Vernier
scale or with digital and dial variations are quite popular. In a physics
lab both Inch Micrometer and Metric Micrometer are used. In case a metric or
inch micrometer is used without vernier then smaller measurement readings
than those graduated, can be got by a visual interpolation between the
graduations.
Do You Know?
The Micrometer was invented by William Gascoigne (1612 – 1644) an
English astronomer and a mathematician. Initially William Gascoigne used
the Micrometer to measure the distances between stars. Only later on was
the Micrometer adapted for measuring small dimensions. |
If a vernier scaled is added to the ordinary Micrometer it is
called a Vernier Micrometer. With the addition of a vernier to a Micrometer,
taking precise readings of one ten-thousandth of an inch becomes distinctly
possible. The vernier markings appear on the sleeve of a micrometer. They
are infact parallel to the thimble markings.
How to Select the Right Micrometer
Selecting the appropriate Micrometer is a challenging task especially if
there is a wide range of items that need to be measured. Some of the broad
points to be considered is given here.
- Readability Features : Gives accurate, instant and direct
readings. An uniform spindle pressure for all the readings along with
decimal equivalents on inch tools.
- Ease-of-Handling Features : A balanced frame and thimble
design. A Ring-type knurled lock nut helps to secure a quick and firm
locking.
- Accuracy and Long-Life Features : Rigid one-piece frame using
drop forged steel is preferred. For a good accuracy a hard and stable
single piece spindle is best.
- Range of the Micrometer : It is the entire range length or
dimensional range which can be measured by the gage.
Parts of a Micrometer
Some of the major parts of a Micrometer is described here.
Anvil : It is the part toward which the spindle moves. The
measurable object rest against an Anvil.
Spindle : Spindle is a cylindrical part which makes a push towards
the anvil by the action of a thimble.
Thimble : The component that one's thumb turns.
Frame : Frame is a typically a C-shaped body. Its use is for holding
the anvil as well as the barrel in constant relation with each other. The
thick shape of the frame is for minimizing flexion, expansion, and
contraction, than can distort the Micrometer.
Lock Ring : Lock-ring is essentially the knurled part. It can be
tightened for holding the spindle stationary, to say for momentarily keeping
a measurement on hold.
Rachet : The Rachet is turned clockwise for perfectly trapping the
object to be measured in between an anvil face and the spindle face. On
perfect tightening the Rachet makes a clicking’ noise indicating that
the reading of the measurement can now be taken.
Types of Micrometer
Outside
Micrometer
An outside micrometer is for typically measuring the external dimensions of
objects such as shafts, wires, spheres, blocks etc. Outside Micrometers are
also known as External Micrometers.
Inside
Micrometer
The Inside micrometer is used for measuring accurately and conveniently the
openings of holes or cavities. Internal micrometers are quite adept in
measuring the inner diameter (ID) or an inside feature of a part or
component.
Depth
Micrometer
In Depth Micrometer a spindle is projected via a flat and precisely
machined bar. Depth Micrometres are typically used for measuring accurately
the inside diameter of holes, slots, bores or recesses to within 0.001 of an
inch.
Digital
Micrometer
Digital Micrometer is appropriate for applications where the requirement is
to record accurately the absolute position or differences between two or
more positions. The object that is to be measured is made to fit in between
the metal rods positioned to the left of the digital display.
Some of the features to look for in latest range of Digital Micrometers
include
- Clear and easy-to-read numbers displayed on a digital counter
- Easy recalling of preset measurements
- Provision of position lock
- Display both in metric or English units
- For uniform measurements provision for torque limiting knob
- Automatic shut off
- High resolution
