Standard micrometer

How to Read an Outside Micrometer


 

A micrometer generally provides greater precision than a caliper, but is limited to a smaller range of lengths. For example, it would take a six-piece set of micrometers to cover the range of a 6” caliper.

Parts of an Outside Micrometer




Proper Use and Care for a Micrometer


Be sure to unlock the locking lever before attempting to rotate the thimble.
Clean the measuring faces with a clean cloth before and after measurements.
It is also a good practice to occasionally clean the spindle to keep any contaminants from being drawn into the sleeve. Use the grip on the thimble when requiring a large amount of travel but as you come close to closing in on the object to be measured use the ratchet stop so as to not over tighten the thimble and give an erroneous reading. Never leave a micrometer exposed in the hot sun and then attempt a measurement. This would also lend to an erroneous reading. When a micrometer is at its minimum reading the horizontal line on the sleeve should line up with the ‘0’ on the thimble. If that is not the case it will be necessary to calibrate the micrometer by rotating the sleeve. Each micrometer comes with a half moon adjusting wrench for this purpose. To make the adjustment simply puzzle the wrench to the side of the spindle and insert the small tip into the leverage hole. It will not require much effort to turn the spindle however there is sufficient resistance in the spindle so that it will never move on its own. Larger micrometers are supplied with standards to check for correct calibration. When checking, be sure to hold the standard squarely between the anvil and spindle. To help with this try rotating the standard slightly with your fingers while gently turning the thimble as you close in on the standard.

 

How to read an outside micrometer


Click to go to
1. Reading a .001” scale
2. Reading a .0001” scale
3. Reading a .01mm scale
4. Reading a .001mm scale


First of all, the basics:
The pitch of the screw thread on a standard spindle is 40 threads per inch. One revolution of the thimble advances the spindle face toward or away from the anvil face precisely 1/40" or 0.025" equaling the distance between two graduations on the sleeve. The reading line on the sleeve is divided into 40 equal parts by vertical lines that correspond to the number of threads on the spindle. Therefore, each vertical line designates 1/40" or 0.025". Every fourth line, which is longer than the others, designates 0.100" and is numbered. The beveled edge of the thimble is divided into 25 equal parts with each line representing 0.001" and every line may or may not be numbered however every fifth line is numbered consecutively. To read the micrometer in thousandths, multiply the number of vertical divisions visible on the sleeve by 0.025", and to this add the number of thousandths indicated by the line on the thimble which best coincides with the central long line on the sleeve.


Now some examples:

How to read a micrometer graduated in 0.001"


Micrometer thimble showing 0.276 inch

In the picture above, the thimble is positioned to where it is setting between the 2nd and 3rd numbered graduation thus 2 x 0.100” = 0.200”. Past that there are three additional sub-divisions, which is 3 x .025” = 0.075”. Lastly the graduation 1 on the thimble is the closest to the central long line on the sleeve therefore 1 x 0.001” = 0.001”. The reading thus would be 0.200” + 0.075” + 0.001”, totaling to 0.276".


How to Read an Outside Micrometer Graduated in 0.0001" (using the extra vernier scale).

Many micrometers include a vernier scale on the sleeve in addition to the regular graduations. This allows measurements within 0.001 millimeters to be made on metric micrometers, or 0.0001 inches on inch-system micrometers.
The additional digit of these micrometers is obtained by finding the line on the sleeve that best coincides with the line on the thimble. The number of this coinciding vernier line represents the additional digit.


This next example uses a 1” to 2” micrometer (shown with the 1” standard).


The horizontal scale on the sleeve is marked with graduations every .025 (25 thousandths). Every 4th graduation (starting after ‘0’) is numbered consecutively. These numbers represents 0.100 (4 x .025 = 0.100) which is read as 100 thousandths.
The vertical scale graduations on the thimble represent .001 (1 thousandths). Every 5th graduation is numbered for clarity.
The vertical scale graduations on the sleeve represent .0001 (tenth of a thousandths). This is the vernier scale.




Micrometer reading 1.1551 inches

The reading for this example is determined by adding five separate figures.
And these are:
· Length of the standard - 1.0000
· The numbered graduation on the sleeve – ‘1’ or 0.1000
· Two additional graduations on the sleeve – 2nd line past the ‘1’ which is 2 x .025 = .050 (50 thousandths).
· The number of thousandths on the vertical scale of the thimble - between 5 and 6 therefore .005
· The best match up of the two vertical scales which is 1 therefore .0001
Total of all five figures:
1.0000
0.1000
0.0500
0.0050
0.0001
is
1.1551 which is simply read as “1.1551 inches” or could be read as “one and one thousand five hundred fifty one ten-thousandths of inches”.




Another example in inches using a 0” to 1” micrometer:



 


How to read a micrometer graduated in 0.01mm


The pitch of the screw thread on a metric spindle is one-half millimeter (0.5mm). One revolution of the thimble advances the spindle face toward or away from the anvil face precisely 0.5mm. The reading line on the sleeve is graduated above the central long line in millimeters (1.0mm) with every fifth millimeter being numbered. Each millimeter is also divided in half (0.5mm) below the central long line. The beveled edge of the thimble is divided into fifty equal parts, with each line representing 0.01mm and every fifth line being numbered from 0-50. Thus, the number of millimeter and half-millimeter divisions visible on the sleeve plus the number of hundredths of a millimeter indicated by the thimble graduation, which coincides with the central long line on the sleeve, give the reading.


Micrometer thimble reading 5.78mm

In the picture above, the thimble is positioned to where the edge of the thimble bevel is positioned between the 5th and 6th graduation on the upper side of the scale thus 5.0millimeter. It is also past the next graduation on the lower side of the scale thus an additional 0.5mm. Finally graduation 28 (.28) on the thimble coincides with the central long line on the sleeve. The reading then would be 5.00 + 0.5 + 0.28 = 5.78 mm.



How to read a micrometer graduated in 0.001mm

Micrometer reading 5.783millimeters

In the above picture this micrometer has the additional vernier scale on the sleeve. It is reading about the same as the previous example however a more accurate reading can be obtained with this vernier scale. The #31 graduation on the thimble lines up best with the .003 graduation mark on the sleeve. Thus the reading would be 5.00 + 0.5 + 0.28 + .003 = 5.783mm.


For accurate readings on all precision measurements it is important to hold the work piece squarely with the measuring tool. Consider purchasing a micrometer stand that can serve as a ‘third hand’. A stand can greatly improve the accuracy of a measurement and actually speed up the process especially when measuring parts repetitiously.



 

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Micrometers - Measuring instruments

The micrometer consist of a semicircular frame having a cylidrical extension, the barrel (sleeve), at its right end and a hardened anvil at the other end. The bore of the barrel (sleeve) is threaded and a spindle screws into the bore. The spindle carries a graduated thimble which turns at one with it.

Micrometers - Measuring instruments

There are three types of micrometers which are commonly used: the outside micrometer, the inside micrometer, and the depth micrometer.

OUTSIDE MICROMETERS

Outside micrometers are used to measure an outside distance or diameter to an accuracy of .001 of an inch.

INSIDE MICROMETERS

Inside micrometers are used to measure an inside diameter to an accuracy of .001 of an inch.

DEPTH MICROMETERS

Depth micrometers are used to measure depths to an accuracy of .001 inches.

- Parts of the micrometer

Parts of the micrometer

Micrometers have been fitted with two refinements which are great help to the user. The first of these is the spindle lock which is a device which enables the spindle to be positively locked in any positions. The micrometer can be set to a desired position and then locked. The second refinement is the ratchet stop and this is a device placed  on the end of the thimble. Only a relatively slight pressure on the thimble can result in a considerable force being exerted between the two anvils. If the force were to be excessive then it would be possible to overstress the frame thus causing permanent damage to the micrometer which would in turn lead to incorrect readings being obtained. To overcome this problem the ratched stop is fitted and this drives the thimble through a ratchet device.

Reading an imperial micrometer

Reading a micrometer is only a matter of reading the micrometer scale or counting the revolutions of the thimble and adding to this any fraction of a revolution. The micrometer screw has 40 threads per inch. This means that one complete and exact revolution of the micrometer screw moves the spindle away from or toward the anvil exactly 1/40 or 0.025 inch.

The lines on the barrel conform to the pitch of the micrometer screw, each line indicating 0.025 inch, and each fourth line being numbered 1, 2, 3, and so forth. The beveled edge of the thimble is graduated into 25 parts, each line indicating 0.001 inch, or 0.025 inch covered by one complete and exact revolution of the thimble. Every fifth line on the thimble is numbered to read a measurement in thousandths of an inch.

Reading an imperial micrometer

- TO READ A MEASUREMENT AS SHOWN ABOVE.

Read highest figure visible on barrel.. . . . . 3 x 0,1in = 0.300 in.

Number of lines visible between the No. 3 and thimble edge. . . . . . . 1 x 0,025in = 0.025 in.

The line on the thimble that coincides with or has passed the revolution or long line in the barrel   . . .. . . . 16 x 0,001in = 0.016 in.

TOTAL = 0.300in + 0,025in +0,016in = 0,341in

 Reading a metric micrometer

The same principle is applied in reading the metric graduated micrometer, but the following changes in graduations are used: The pitch of the micrometer screw is 0.5 mm. One revolution of the spindle advances or withdraws the screw a distance equal to 0.5 mm.

On the barrel the datum line is graduated with two sets of lines, the one below the datum reading in millimetres and the set above reading in half millimetres. The thimble scale is marked in fifty equal divisions, figured in fives, so that each small division on the thimble represents 1/50 of 1/2mm which equals 1/100mm , which is 0,01mm.

Reading a metric micrometer

- TO READ MEASUREMENT AS SHOWN ABOVE:

First note the whole number of mm divisions on the barrel (major divisions below datum line) ........... 15 x 1,0mm = 15,00mm

Then observe whether there is a half mm visible (minor  divisions above datum line)............3 x 0,50mm = 1,50mm

Finally read the line on the thimble coinciding with the datum line. This gives hundredths of a mm. ........... 16 x 0,01mm = 0,16mm

TOTAL: 15,00mm = 1,50mm + 0,16mm = 16,66mm

DIGITAL MICROMETERS

Digital micrometer is very accurate and does involve the computations needed by a standard micrometer. When the spindle and anvil come in contact with the workpiece, the measurement can be read directly from a digital display.

CARE OF THE MICROMETERS

  1. Coat metal parts of all micrometers with a light coat of oil to prevent rust.
  2. Store micrometers in separate containers provided by manufacturer.
  3. Keep graduations and markings on all micrometers clean and legible.
  4. Do not drop any micrometer. Small nicks or scratchescan cause inaccurate measurements.
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A micrometer is a tool that measures the size of a target by enclosing it. Some models are even able to perform measurements in units of 1 μm. Unlike hand calipers, micrometers adhere to Abbe’s principle, which enables them to perform more accurate measurements.
In general, the term "micrometer" refers to outside micrometers. A variety of other types of micrometers also exist according to different measurement applications. Examples include inside micrometers, bore micrometers, tube micrometers, and depth micrometers. The measurable range differs every 25 mm—such as 0 to 25 mm and 25 to 50 mm—depending on the size of the frame, so using a micrometer that matches the target is necessary. Recently, digital micrometers have become incredibly popular.

Abbe’s principle states that, "In order to improve measurement accuracy, the measurement target and the scale of the measuring instrument must be placed in a collinear fashion in the measurement direction." With micrometers, the scale and the measurement position are collinear, so these instruments follow Abbe’s principle. As such, micrometers can be said to have high measurement accuracy.

Structure and usage of a micrometer
  • Place the target between the anvil and the spindle, and then turn the thimble to lock the target between the two surfaces.
  1. Before measurement, wipe down the anvil and spindle surfaces with a clean cloth. This removes dirt and dust from the surfaces, which enables accurate measurements.
  2. To hold the micrometer, hold the heat-resistant plate on the frame with the thumb and index finger on your left hand, and pinch the thimble between the thumb and index finger on your right hand.
  3. Grip the target between the anvil and the spindle, turn the ratchet stop until it slips, and then read the value.
  4. Read the value from the main scale on the sleeve and the scale on the thimble. Use the line on the right edge of the sleeve to read the value in units of 0.5 mm. You can then use the scale at which the center line on the thimble (scale) lines up to read the value in units of 0.01 mm.
How to Use a Micrometer
  • Use a gauge block or a dedicated gauge to calibrate a micrometer. In order to perform accurate measurements, the anvil surface must always be flat. After multiple measurements are performed, the surface may become no longer flat due to wear and the accumulation of dirt. Therefore, periodically use a part known as an optical flat to check whether the surface is flat according to the displayed Newton's rings.
  • When measuring a metal target and when performing calibration with a gauge block, exercise caution with respect to thermal expansion. Whenever possible, avoid holding metal with bare hands, or use gloves that do not transmit heat and are designed for precision work.
  • The calibration interval of micrometers is 3 months to 1 year.

INDEX

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Micrometer Setting Standard

Length: 100mm

Item number: 167-104

167-103_z.eps
167-103_z.eps
167-001_a1.jpg

Micrometer Setting Standard

Length: 100mm

Item number: 167-104

Suggested retail price: 32.00 €*

Used for adjusting the reference point of outside micrometers

*VAT excluded. All products are intended to be sold to commercial customers.

Product illustrations are without obligation. Product descriptions, in particular any and all technical specifications, are only binding when explicitly agreed upon.

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Micrometer standard

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