How Does Micrometer Screw Gauge Works & How to Read

When listing precision measuring instruments, a micrometer screw gauge must be among them. It is one of the older precision measuring tools capable of measuring smaller dimensions that vernier calipers cannot measure.

Micrometer screw gauges are precision instruments purposely designed for taking small measurements with high accuracy. They are often used in metalworking, mechanical engineering, and laboratory settings.

We use these precision tools to measure objects’ dimensions to the hundredths of a millimeter (0.01 mm). They can also measure thousandths of an inch (0.001 inch). Well, in this reading, we’ll explore what a micrometer is, its parts, diagram, types, how it works, and how to read it.

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Table of Contents

What is a Micrometer Screw Gauge?

A micrometer screw gauge is a device widely used in the mechanical engineering field for measuring tiny dimensions. Though it belongs to the family of calipers, it also consists of two different scales. Hand tools are used in telescopes or microscopes to measure the potential diameter of microscopic objects.

Micrometers are not always in the form of calipers, but their spindle is a very accurately machined screw. The part to be measured will be placed between the spindle and the anvil. This spindle moves toward the object to be measured when the ratchet knob is turned and the object is lightly touched against the anvil.

In the 17th century, William Gascoigne invented the first micrometric screw as an improvement of the vernier. A telescope used it to measure the angular distances between stars and the relative sizes of celestial objects.

A micrometer is a neoclassical coinage word from Greek, micros meaning ‘small’ and metron meaning ‘measure.’ It has been micrometers, Merriam-Webster, that English got it from French.

In the early 19th century, Henry Maudslay developed a bench micrometer. He was given the jocular nickname “the Lord Chancellor” among his staff because of the micrometer’s final judgment on measurement accuracy and the micrometer in the firm’s work. In 1844, details of Whitworth were published.

Micrometer Parts

The various parts of a micrometer screw gauge are frame, anvil, spindle, sleeve, thimble, ratchet, screw, and lock.

Frame: this is the c-shaped body of the instrument. It holds and supports the anvil and the barrel.
Anvil: this part put the measuring surface in fixed position against the object to be measured is placed
Spindle: is the part that moves parallel to the anvil when the thimble is rotated, allowing for the measurement of objects.
Sleeve (or Barrel): is a stationary cylindrical component marked with a scale in millimeters or inches, providing the main unit measurements.
Thimble: is the rotating part that fits over the sleeve, marked with a circular scale that provides further precision to the measurement.
Ratchet Stop: A mechanism used to apply a consistent measuring force to ensure repeatable and accurate measurements.
Lock Nut: A feature used to lock the spindle in place once a measurement has been taken, allowing for easy reading without the risk of altering the setting.

Diagram Micrometer Screw Gauge

How Does a Micrometer Work?

Micrometers use screws to translate small distances into large screw rotations, which a scale can read. A differential screw is one of the thread forms that determine a micrometer’s accuracy.

The screw’s lead is a constant that correlates the amount of rotation with axial movement, and vice versa. The lead is the distance the screw moves forward axially with one complete turn (360°).

An appropriate lead and major diameter of the screw amplify a given amount of axial movement in the resulting circumferential movement. For example, if the lead of a screw is 1 mm and the major diameter is 10 mm, the circumference of the screw is 10π, or about 31.4 mm.

This amplification allows a small difference in the sizes of two similar measured objects to correlate to a larger difference in the position of a micrometer’s thimble.

Scale markings on the thimble and sleeve directly determine the position of the thimble in classic-style analog micrometers. A vernier scale is often included, allowing the position to be read to a fraction of the smallest scale mark.

Digital micrometers display the length digitally on an LCD, while mechanical-digit versions exist, like car odometers where numbers “roll over.”

Watch the video below to learn the working of a micrometer:

How to Read a Micrometer?

Before using a micrometer tool for measurement, ensure it is English or metric and has the same unit of measure as your current tool. Rotate the micrometer into the correct measurement and add the numbers found on the spindle and thimble for accurate results.

The type and design of the micrometer determine how to find desired numbers, and the manufacturer provides instructions on how to read the micrometer.

A micrometer is a tool used for precise measurement of various objects, including the size of pipes, tools, and hollow objects. It can measure the inside width of a pipe or bearing or the depth of a hole or recess.

Accuracy is crucial in machines with moving parts, as parts that move in and out of each other need to remain in a steady, straight line. Applications such as bearings, pipe fittings, and sheet metals rely on micrometers to determine the crucial thickness of items.

In essence, micrometers are the preferred tool for precise measurement in various applications, ensuring the safety and integrity of the object being measured.

Things to Know While Using Micrometer

First, know the instrument; note the movable and stationary parts. Before taking any measurement, ensure you clean the spindle and anvil. Use a paper or a clean cloth for this.

When cleaning, place the cleaning material in the midst of the spindle and the anvil and tighten the setup slightly until the paper or cloth is jammed, then pull it out. This step helps to take accurate measurements.

You can now take the measurement by positioning the object between the spindle and the anvil. You should place the object against the anvil due to its stationary nature. We expect you to place the object properly to prevent it from shaking during the measurement process.

The ratchet counter is rotated clockwise to tighten the spindle; ensure that the thimble zeros are parallel to the line of the scale on the sleeve. The spindle is tightened against the object and force should be applied until the clickable thimble clicks three times.

Lock the thimble while the object is forcefully placed. The spindle is still movable even as the thimble is locked. This approach helps to get a precise measurement.

Exercise caution when measuring the object, as it may compromise the accuracy of the screw gauge. Please record the reading before unlocking the spindle, and then remeasure the entire setup to verify the measurement.

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