Micrometer: Types, Parts, Principle, How to Read (mm & inches) | How to read a Micrometer

Today you will learn types of micrometer, parts of micrometer, working principle of micrometer and at the last how to read a micrometer in mm and inches with an example.

Micrometers are precision measuring instruments used for making accurate measurements of small distances or thicknesses. They are commonly used in manufacturing, engineering, and scientific research to measure the thickness of materials, the diameter of wires or screws, and the depth of holes, among other things.

Micrometers typically consist of a U-shaped frame with a measuring spindle mounted on one end and a thimble on the other. The spindle moves along a finely threaded screw, allowing for precise adjustments to the measurement. The thimble is marked with a scale that is used to read the measurement, typically in thousandths of an inch or hundredths of a millimeter.

To take a measurement with a micrometer, the object being measured is placed between the spindle and anvil (a flat surface at the end of the frame opposite the spindle) and the thimble is rotated to bring the spindle into contact with the object. The measurement is then read off the scale on the thimble.

Micrometers come in a variety of types and sizes, including outside micrometers for measuring the outside diameter of objects, inside micrometers for measuring the inside diameter of holes, and depth micrometers for measuring the depth of holes or slots. Digital micrometers are also available, which provide a digital readout of the measurement for greater accuracy and convenience.

Table of Contents

What is a Micrometer?

A micrometer, also known as a micrometer screw gauge, is a precision measuring tool used to measure very small distances or thicknesses with a high degree of accuracy. It is commonly used in manufacturing, engineering, and scientific research for measuring the diameter of wires, the thickness of materials, and the depth of holes, among other things.

Micrometers typically consist of a U-shaped frame with a measuring spindle mounted on one end and a thimble on the other. The spindle moves along a finely threaded screw, allowing for precise adjustments to the measurement. The thimble is marked with a scale that is used to read the measurement, typically in thousandths of an inch or hundredths of a millimeter.

To take a measurement with a micrometer, the object being measured is placed between the spindle and anvil (a flat surface at the end of the frame opposite the spindle) and the thimble is rotated to bring the spindle into contact with the object. The measurement is then read off the scale on the thimble.

Micrometers come in a variety of types and sizes, including outside micrometers for measuring the outside diameter of objects, inside micrometers for measuring the inside diameter of holes, and depth micrometers for measuring the depth of holes or slots. Digital micrometers are also available, which provide a digital readout of the measurement for greater accuracy and convenience.

Types of Micrometer

There are several types of micrometers, each designed for specific measurement applications. The most common types of micrometers are:

How to read a Micrometer
How to read a Micrometer

Outside Micrometer

This is the most common type of micrometer used for measuring the outside diameter of objects, such as pipes, rods, or screws. It typically has a measuring range of 0-25mm to 0-300mm.

Inside Micrometer

This type of micrometer is used for measuring the inside diameter of objects, such as holes or tubes. It consists of a micrometer head with a set of measuring rods of different sizes that can be attached to the head to measure different diameters.

Depth Micrometer

This type of micrometer is used for measuring the depth of holes or slots. It consists of a long, slender spindle and anvil that can be inserted into a hole or slot to measure its depth.

Screw Thread Micrometer

This type of micrometer is used for measuring the pitch diameter of screw threads. It consists of a micrometer head with special anvils that are designed to fit over the threads.

Vernier Micrometer

This type of micrometer has a vernier scale that allows for more precise readings. It is commonly used in laboratory and research settings where high accuracy is required.

Digital Micrometer

This type of micrometer provides a digital readout of the measurement, which can be more accurate and easier to read than traditional micrometers. It is often used in manufacturing and engineering applications where precise measurements are critical.

The main parts of a micrometer include

Micrometer Parts
Micrometer Parts

Frame

The frame is the main body of the micrometer that houses the internal components.

Anvil

The anvil is a flat surface at the end of the frame opposite the spindle that rests against the object being measured.

Spindle

The spindle is a small, pointed rod that extends from the frame and moves along a finely threaded screw to make precise adjustments to the measurement.

Thimble

The thimble is a rotating sleeve that is attached to the frame and is used to read the measurement. It is marked with a scale that corresponds to the movement of the spindle.

Ratchet stop

The ratchet stop is a small lever that is used to apply a consistent amount of force to the object being measured, ensuring accurate and repeatable measurements.

Locking mechanism

The locking mechanism is used to lock the spindle in place once the measurement has been taken, preventing any further movement and ensuring the accuracy of the measurement.

Barrel

The barrel is the cylindrical part of the frame that houses the spindle and screw.

Scale

The scale is marked on the thimble and barrel and is used to read the measurement. It is typically calibrated in thousandths of an inch or hundredths of a millimeter.

Sleeve

The sleeve is a stationary component of the micrometer that surrounds the barrel and provides a reference point for the measurement.

Working Principle of Micrometer 

The working principle of a micrometer is based on the linear displacement of a spindle along a precisely threaded screw. The spindle moves along the screw when the thimble is rotated, causing the spindle to move towards or away from the anvil.

To take a measurement with a micrometer, the object being measured is placed between the spindle and the anvil, and the thimble is rotated until the spindle just touches the object. The measurement is then read off the scale on the thimble.

The micrometer works on the principle of using a screw to amplify the rotational movement of the thimble to produce a linear displacement of the spindle. The screw has a very fine pitch, typically around 0.5 mm, which means that the spindle moves by a very small amount for each rotation of the thimble.

The measurement range of a micrometer is determined by the length of the screw and the number of revolutions of the thimble needed to move the spindle the entire length of the screw. Micrometers typically have a measuring range of a few millimeters to several centimeters, depending on the size of the micrometer.

Micrometers are designed to provide accurate and precise measurements of small dimensions, typically to within a few thousandths of an inch or hundredths of a millimeter. They are widely used in engineering, manufacturing, and scientific research where accurate measurements are critical for ensuring the quality and reliability of products and processes.

How to Read a Micrometer in mm?

To read a micrometer in millimeters (mm), follow these steps:

Micrometer Readings in mm
Micrometer Readings in mm

Clean the micrometer

Make sure the micrometer is clean and free from any dirt or debris that could interfere with the measurement.

Choose the correct micrometer

Choose a micrometer that has a measuring range that is appropriate for the object you want to measure.

Place the object to be measured

Place the object to be measured between the spindle and anvil of the micrometer.

Close the micrometer

Close the micrometer by turning the thimble clockwise until the spindle just touches the object being measured.

Read the measurement

Read the measurement on the sleeve and thimble of the micrometer. The sleeve is marked with millimeter (mm) graduations and the thimble is divided into 50 or 100 equal parts, each representing 0.01 mm or 0.005 mm respectively.

Add the readings

To get the final measurement, add the reading on the sleeve to the reading on the thimble. The sleeve reading represents the whole millimeter while the thimble reading represents the fraction of a millimeter.

Estimate the final digit

If the thimble is not exactly on a graduation mark, estimate the final digit by noting the number of lines visible on the circular scale and multiplying by the smallest increment for the thimble (0.01 mm or 0.005 mm).

For example, if the sleeve reading is 5 mm and the thimble reading is 0.25 mm, the final measurement would be 5.25 mm. If the thimble reading was between the 20th and 21st line on the circular scale, the final digit would be estimated as 0.005 mm, making the final measurement 5.255 mm.

Note: Some micrometer manufacturers can reverse the position of full and half millimeters graduations and but The order in which you read the micrometers remains the same.

Zero Error of a Micrometer 

A micrometer can have a zero error, which means that the zero point of the micrometer’s scale does not align with the actual zero point when the spindle and anvil are in perfect contact with each other.

There are two types of zero errors in a micrometer: positive zero error and negative zero error.

Positive Zero Error

When the micrometer’s thimble scale reads a positive value even when there is no gap between the spindle and the anvil, this is known as a positive zero error. In this case, the actual measurement is larger than the reading on the micrometer.

Negative Zero Error

When the micrometer’s thimble scale reads a negative value even when there is no gap between the spindle and the anvil, this is known as a negative zero error. In this case, the actual measurement is smaller than the reading on the micrometer.

It is essential to check the micrometer for zero error before taking any measurements to ensure the accuracy of the readings. To check for zero error, close the micrometer with the spindle and anvil in contact and note the reading on the thimble scale. If the reading is not zero, then there is a zero error, and the correction must be applied to the readings obtained during measurement.

To correct for zero error, add or subtract the value of the error from the actual measurement obtained from the micrometer, depending on whether the zero error is positive or negative, respectively.

Methods of Removing Zero Error

There are two methods for removing zero error in a micrometer:

By adjusting the spindle or anvil

In this method, the position of the spindle or anvil is adjusted to correct the zero error. To do this, loosen the lock nut on the micrometer and turn the spindle or anvil until the thimble reads zero when the spindle and anvil are in contact. Then, tighten the lock nut to secure the position of the spindle or anvil.

By adding or subtracting the zero error

In this method, the zero error is noted during calibration and is added or subtracted from the readings obtained during measurement. For example, if the micrometer has a positive zero error of 0.02 mm, then this value is subtracted from the readings obtained during measurement to obtain the correct measurement.

It is essential to note that the correction for zero error must be done carefully to avoid introducing another error into the measurement. It is recommended to calibrate the micrometer periodically to ensure that it is accurate and to check for any zero error. It is also recommended to use a micrometer with a digital display as it reduces the chances of making an error when reading the scale.

Test Pieces of Micrometer

Test pieces of micrometer are objects that are specifically designed to verify the accuracy and precision of a micrometer. They are used to calibrate micrometers and ensure that they are reading correctly. There are various types of test pieces for micrometers, including:

Micrometer Reading in inches
Micrometer Reading in inches

Setting standards

These are precision blocks or rods that are used to set the zero point or reference point of the micrometer. They are made of high-quality materials such as steel or tungsten carbide, and their dimensions are known and certified.

Step gauges

These are blocks or rods that have a series of steps of known dimensions. They are used to check the accuracy of the micrometer over a range of sizes. Step gauges can be made of steel, ceramic or other materials, and they come in various sizes and shapes.

Ring gauges

These are circular gauges with a known inside or outside diameter. They are used to check the accuracy of the micrometer for measuring internal or external dimensions. Ring gauges are made of steel or ceramic, and they come in various sizes and shapes.

Thread pitch gauges

These are gauges with a series of threads of known pitch. They are used to check the accuracy of the micrometer for measuring the pitch diameter of screws and other threaded components. Thread pitch gauges are made of steel or plastic, and they come in various sizes and thread pitches.

Spheres or balls

These are precision balls of known diameter, used to check the accuracy of the micrometer for measuring the diameter of round objects. Spheres or balls are made of steel, tungsten carbide or ceramic, and they come in various sizes.

It is important to use the appropriate test piece for the micrometer being calibrated to ensure accurate readings. The test pieces must also be maintained and stored carefully to prevent damage or wear, which could affect their accuracy.

Care and Maintenance

Proper care and maintenance of a micrometer are essential to ensure its accuracy and longevity. Here are some tips for caring and maintaining your micrometer:

Clean the micrometer after use

Use a soft, clean cloth to wipe the micrometer clean after each use. Do not use harsh chemicals or abrasive materials, as these can damage the measuring surfaces.

Store the micrometer properly

Keep the micrometer in a protective case or pouch when not in use to prevent dust, dirt, or other debris from accumulating on the measuring surfaces. Store the micrometer in a dry, clean environment away from excessive heat, cold, or humidity.

Check for zero errors

Regularly check the micrometer for zero errors to ensure accurate readings. If a zero error is detected, correct it before using the micrometer.

Lubricate the micrometer

Apply a small amount of oil to the moving parts of the micrometer to ensure smooth operation. Be sure to use a lubricant that is recommended by the manufacturer.

Handle the micrometer with care

Avoid dropping or banging the micrometer, as this can damage the measuring surfaces or the internal mechanism. Use the micrometer only for its intended purpose and handle it with care.

Calibrate the micrometer regularly

Calibrate the micrometer periodically, according to the manufacturer’s instructions, to ensure that it is accurate and reliable.

By following these tips, you can help ensure the accuracy and longevity of your micrometer.

FAQ for Micrometer

Which part of the outside micrometer ensures a uniform pressure between the measuring surface?

The measuring faces of the outside micrometer ensure uniform pressure between the workpiece and the spindle anvil, thus providing accurate measurements.

To read a micrometer you first read the?

To read a micrometer, you first read the main scale or sleeve reading, which gives you the whole units and tenths of units.

An outside micrometer has a negative error the correct reading can be taken by?

If an outside micrometer has a negative error, the correct reading can be taken by subtracting the error from the measured value.

How many divisions are graduated on thimble?

The number of divisions graduated on the thimble of a micrometer varies depending on the model and manufacturer, but typically, there are 50 or 100 divisions on the thimble.

Which part is the measuring face fitted to the frame of the outside micrometer?

The measuring face is fitted to the frame of the outside micrometer’s anvil.

What is the use of a tube micrometer?

A tube micrometer is used for measuring the wall thickness of tubes and pipes.

Which type of micrometer is used to measure the exact depth of holes?

A depth micrometer is used to measure the exact depth of holes.

Which spanner is used for zero setting in an outside micrometer?

A small spanner called a “micrometer spanner” is used for zero setting in an outside micrometer.

What is zero error in a micrometer?

Zero error in a micrometer is a deviation from zero on the micrometer’s scale when the measuring faces are brought into contact with each other, which can result in incorrect measurements.

A digital micrometer is used to measure?

A digital micrometer is used to measure the thickness, diameter, and depth of small parts with high accuracy and precision.

What are the parts of a micrometer?

The main parts of a micrometer are the frame, anvil, spindle, thimble, sleeve, and measuring faces.

What are the different types of micrometers?

There are several different types of micrometers, including:

1. Outside micrometer
2. Inside micrometer
3. Depth micrometer
4. Screw thread micrometer
5. Blade micrometer
6. Tube micrometer
7. V-anvil micrometer
8. Point micrometer
9. Gear tooth micrometer
10. Digital micrometer

Each type of micrometer is designed for a specific measuring application, such as measuring the outside diameter of a cylindrical object, the depth of a hole, or the thickness of a sheet of material.

3 thoughts on “Micrometer: Types, Parts, Principle, How to Read (mm & inches) | How to read a Micrometer”

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