MICROMETER

A micrometer is a precision measuring instrument, used by engineers. Each revolution of the ratchet moves the spindle face 0.5 mm towards the anvil face. The object to be measured is placed between the anvil face and the spindle face.

Parts of a micrometer

FRAME
The body used to hold the anvil and barrel firmly in their place is called frame , in micro meter screw gauges , thick C shaped frames are used . Their mass helps in minimization of expansion or contraction due to temperature some manufacturers also deliver gauges with insulated frames to serve the above mentioned purpose.

ANVIL
It is the fixed part mounted at one end of frame exactly parallel to the moving spindle which move towards it , Anvil face which comes directly in contact to the object being measured is machined extremely fine so to achieve highest degree of precision.

SPINDLE
The cylindrical part which displaces by rotation of thimble decreasing the clearance between itself and anvil until the object being measured become stable between the two of them , in modern micrometer screw gauges , anvil and spindle`s open face are tipped with carbide.

SLEEVE/BARREL
The stationary part with having linear scale onto it, called the main scale, it also covers the screw mechanism of screw gauge , now screw gauges are available with adjustable sleeves which makes it easy to eliminate the zero error.

SCREW
It is the most important part of instrument because all measurement is done through it in fact. Very fine stainless steel screws are used for this purpose with a definite pitch.

THIMBLE
It is the part through which measuring screw is rotated, this screwing results in the displacement of spindle and thimble itself.

RATCHET
Ratchet is itself a small device which is used to provide a limited applied force , It is installed at the right end of screw gauge , ratchet acts as a safety device for instruments and also adds more precision in measurement . Final adjustment is made by a making three turns of ratchet.

LOCKING DEVICE
It is actually a nut whose operation is facilitated by means of a lever, usually used to hold tight the spindle at its place so that current reading of that time could be maintained up to a desired length of time.

SCALES
Micrometer screw gauge comes with two scales, one rotating scale which can be found on its rotating cylindrical part it is also called circular scale and the other one can be found on its stationary sleeve which is called main scale or sleeve scale , some designs of instrument can also have a vernier scale as well.

HOW TO READ A MICROMETER?

Watch this video of steps in reading a micrometer caliper.