# Use and reading of the micrometer in hundreth of millimeter

## Use of the instrument of measurement 'micrometer' in the metric system and centesimal resolution: reading and interpretation

The micrometer is an instrument of portable measure, not so versatile, but with good precision when used correctly.

It is not much versatile, beyond other reasons, because its range of measurement is restricted to one inch beyond this, it has a loss of time relativily big in the tasks of adjustment of the measure to be done.

This text assume that you are familiar with the nomenclature of components of the Micrometer <- if necessary, make a review here and with the reading of the ruler, or line gauge, in millimeter <- review by click in here.

## Before use: adjust the micrometer

I'm deciding to 'turning to zero the micrometer' the operation of adjustment of teh instrument that is to close in in a known measure, for example: the zero or with help of a pattern, and helping with a aquired key, align the 'reference line of the sleeve' with the zero mark (0) of the thimble. Evidently, it must make use of the 'turnstile' to close it. By the way, the same number of turns of the turnstile must be repeated in each measure. See the process of taking a measure in the page: use of micrometer .

## The micrometer operation

figure 1 - Thimble in partial view to reveal the divisions of millimeter and half millimeter in the sleeve scale

A pair of male thread/female it has the step and adjusts for beeing calibrated. Solidary to the spindle, it has the thimble and its circumference is marked by equidistant lines. A complete turn in the thimble (and of the spindle) produces an advance equal to the thread. This spindle, usually, has thread with useful length slightly larger than 25 millimeters.

In the sleeve a graduation that controls the advance of the thimble / spindle -figure 1. Usually, this marks are 1 millimeter away from the others. It has also marks to control the advance of half millimeter (0.5mm - below from the reference line, in the sleeve scale), because, how we saw, a complete turn of the spindle produces an advance of 0.5mm.

## The resolution of the micrometer

By definition: 'resolution' is the 'lower difference between indications of a display device that can be perceived', it is the lower measure that can be referred by an instrument of measurement, for example.

In the centesimal micrometer, the resolution is obtained dividing the step of the thread pitch of the micrometer spindle by the number of divisions of the thimble scale (Resolution = pitch of thread of micrometer/ number of divisions of the thimble scale) or Resolution = 0.5mm / 50 = 0.01mm

## The centesimal resolution (hundredth)

figure 2 - image of graduation of the thimble scale rectified to reveal the 50 marks/divisions

The configuration most find in the metal mechanic offices, in Brazil, is the spindle of micrometer that has a step of 0.5mm and the thimble of 50 divisions -figure 2. This way, to turn the micrometer spindle, each mark of spindle that pass by 'reference line' will indicate that the mobile jamb walked away (or closer) 0.01mm (one hundredth of a millimeter).

## Reading of micrometer in centesimal millimeter

To determine the value of teh measurement, it is necessary to sum:

• the value read in the scale graved in the sleeve, in millimeter
• repesented by ( o ) 'in green color' in the animation below
• with 0.50mm in case of the counter of half millimeter it will be exposed
• repesented by ( o ) 'in blue color'
• with the value of the spindle aligned with the 'reference line', in centesimal millimeter
• repesented by ( o ) 'in the orange color'

animation 1 - reading of the measure by the sum of the parcels

Tips
- click in the icon in the inferior corner of the animation screen 1 to change the value of the measurement
- use the icon 'eye' to hide the total values and partial
- with the 'closed eye', click in the colored circles shows the partial value related to them