Linear measurement

The Micrometer Operating principle: a circular movement of a threaded spindle produces an axial movement. The distance moved by the spindle (axial or linear movement) per revolution (circular movement of the thimble) depends on the pitch of the threaded Spindle.

Advantages of micrometer over V.C. : Easier and clearer readability, Lesser observational errors due to parallax, Portable, Easy to handle, Easy operation, Reasonable cost.

The accuracy of the micrometer is governed by the Lead error. Question???? If the value of the measurand 0.45 in what is the expected Uncertainty or error in Measurement? The calibration chart for the micrometer. X-axis is the value of the reference Y-axis is the error in measurement (reference – reading of the micrometer)

Reading the micrometer Reading uncovered on the barrel + 0.01* number of divisions on thimble scale which coincides with horizontal line on the barrel.

The measurement to a third degree of decimal can be made with micrometer by employing vernier scale along with the thimble and barrel divisions. This vernier scale is employed on the barrel or sleeve

10.5+16*0.01 +3* 0.002 inside micrometer

Reading the Vernier micrometer Scale: Reading on micrometer = Reading uncovered on the barrel + acuracy of sleeve * number of divisions on the thimble scale that is just below that on the horizontal line on barrel + Accuracy of vernier * number of divisions on the vernier scale that coincides with horizontal line on thimble

Reading the vernier micrometer

Errors in reading: Lack of flatness of anvil, Inaccurate setting to “Zero” reading before use, Lack of parallelism between anvil and spindle or anvil and workpiece.

Cleaning of micrometer : Clean after every time of use, should never be dunked in solvent or kerosene as a whole, should always remain free from oil, dust, grit or dirt.

Precautions : (1) Apply workpiece gently between spindle and anvil, (2) Use proper size for proper dimensions, (3) Follow proper method of handling, (4) Regularly inspect parts and make sure that spindle moves freely.

Accuracy with micrometer measurements depends on : (1) Degree of calibration of spindle movement. (2) Linearity of spindle movement.

Micrometer types Micrometer accessories

Accuracy of the micrometer depends on 1- The parallelism and the flatness of the Measuring surfaces 2- The deflection of the frame (because of the Holding strength) 3- The accuracy of the screw thread 4- Heat transfer 5- Lack of alignment with the object 6- The reading error The use of an optical flat to check The accuracy of the micrometer