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# Use and Reading of the Micrometer in Hundredth of Millimeter

`Reading and interpretation of the micrometer in centesimal millimeter (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.

## Before use: adjust the micrometer

I am using the expression ‘zero out the micrometer’ to describe the operation of adjusting the instrument which is closing it to a known extent, for example: zero or other measurement, with the aid of a standard, and aided by a suitable key, align the reference line of the sheath ‘with the zero mark (0) of the thimble. Obviously, one must use the ‘ratchet’ to close it. Incidentally, the same number of turns of the ratchet must be repeated in each measurement. See the process of taking a measurement on the page: use of the micrometer.

## The micrometer operation

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

A male/ female thread pair has the pitch and calibrated settings. Solid to the spindle is the drum and its circumference is marked by equidistant lines. A complete turn of the drum (and the spindle) produces the advance equal to the pitch of the thread. This spindle, customarily, has thread of useful length a little larger than 25 millimeter.

In the sheath a graduation that controls the advancement of the drum / spindle-figure 1. Generally, these marks are 1 millimeter from the neighbors. There are also marks to control the half millimeter (0.5 mm – in this example, below the reference line), as, as we have seen, a complete revolution of the drum produced advance of 0.5 mm.

## The resolution of the micrometer

By definition: ‘resolution’ is the ‘smallest difference between indications of a display device that can be significantly perceived’, it is the smallest measure that can be referenced by a measuring instrument, for example.

In the centesimal micrometer, resolution is obtained by dividing the pitch of the micrometric spindle by the number of divisions of the drum (Resolution = micrometric spindle pitch / number of drum divisions) or Resolution = 0.5 mm / 50 = 0.01 mm.

## 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) 0.01 mm (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
• Represented 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

#### Virtual micrometer in millimeter hundredths – simulator of use, reading and interpretation

##### Eduardo Stefanelli

Engenheiro por profissão, professor por vocação