In the realm of precision engineering and manufacturing, dimensional metrology equipment plays a critical role in ensuring the accuracy, quality, and conformity of machined and manufactured components and assemblies. Whether measuring incredibly small tolerances or validating complex geometries, a diverse array of metrology equipment and technologies are used to uphold the standards of measurement precision and accuracy. In this thorough guide, we delve into 21 types of dimensional metrology equipment, each designed to tackle specific measurement challenges with varying degrees of accuracy and sophistication. Whether it’s the essential caliper and micrometer for everyday measurements or advanced systems like coordinate measurement machines (CMMs) and laser scanners for detailed 3D analysis, understanding the capabilities and applications of these tools is essential for maintaining excellence in manufacturing and engineering practices. Let’s explore the diverse landscape of dimensional metrology equipment and uncover the tools that drive precision and accuracy in modern industry.
“When you can measure what you are speaking about, and express it in numbers, you know something about it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind” – Lord Kelvin
- Caliper
Calipers are one of the most commonly used pieces of dimensional metrology equipment. They are used to measure dimensions of an object (commonly 6” or less) and are especially effective at measuring diameters and/or depths. Measurement accuracy as close as 0.01 mm is possible, with repeatability dependent on operator skill.
- Micrometer
Similar to calipers, micrometers are a commonly used piece of dimensional metrology equipments for measuring dimensions of an object. Micrometer can allow for greater accuracy and precision due to their design using a calibrated screw mechanism. A micrometer can be accurate on the order of magnitude of 0.01 mm with repeatability dependent on operator skill.
- Height Gage
Height gages are accurate one-dimensional measurement systems used for measuring the height of various objects. They can come in forms such as dial, electronic, or vernier and can be configured to measure various ranges.
- Universal Length Measuring Machine
Universal length measuring (ULM) machines are highly accurate on-dimensional instruments that are effective at measuring external diameters (OD) and internal diameters (ID) of various sizes. The measurement uncertainty can reach sub-micron values in some setups and environments.
- Optical Comparator
Optical comparators are used verify dimensional accuracy through non-contact observation. Objects under test are illuminated from front and/or back lights and observed through visual magnification on a large display. Dimensional features can then be measured and surface defects clearly displayed for determining part quality conformance.
- Surface Profilometer
Surface profilometers are dimensional metrology instruments that measure, analyze, and report topological characterizations of the surface of an object. A profilometer can be used to asses the dimensional form of an object as well as its surface roughness characteristics.
Surface Metrology Original Equipment Manufacturers (OEMs)
- Diametric Air Gage
Diametric air gages are specially designed dimensional metrology equipment used to measure diametric characteristics of bores and cylindrical objects. These instruments use arbors and rings with opposing air jets to accurately measure diameter within a very small calibrated measurement range (e.g. sub-micron accuracy over roughly 10-50 micron range).
- Roundness and Form Measuring Machine
Roundness and form measuring machines are specialized metrology equipment used to measure bores and cylindrical objects. These testing machines have precision spindles and ultra-sensitive indicators that enable precise measurement of form (roundness, straightness, cylindricity, etc.), surface texture, and/or contour.
- Coordinate Measurement Machine
Coordinate measurement machines (CMM) are multi-purpose three-dimensional metrology instruments used to measure a wide variety of features and characteristics. CMMs specialize in dimensional measurements in all three dimensions but can be effectively used to measure many GD&T characteristics.
CMM Original Equipment Manufacturers (OEMs)
- Laser Scanner
Laser scanners are another three-dimensional metrology instrument that captures millions of data points through non-contact laser infrared technology. The point cloud is used to construct a 3D representation of an object or space and analyzed to report its dimensional measurements.
- Interferometer
Interferometers are ultra-precise non-contact dimensional metrology equipment. These Instruments use the interference patterns of light sources to construct the physical surface of the object under test. The data is then analyzed to report dimensional measurements of the object.
Surface Metrology Original Equipment Manufacturers (OEMs)
- Linear Variable Differential Transformer
A linear variable differential transformer (LVDT) is a electromechanical device that converts dimensional position into an electric signal. LVDTs are commonly used in various dimensional metrology applications to report dimensional measurements of a object under test.
- Functional Gage
A functional gage is a specifically design piece of dimensional metrology equipment used to test the conformance of an object under test. This type of gage physically simulates the function of the print datums in order to determine the quality of the form, fit, and function of the object under test.
- Optical Flat and Monochromatic Light
Optical flats are discs of glass made and lapped to be flat within tens of nanometers. When paired with a monochromatic light source, an optical flat can be used to measure the dimensional flatness of an object under test by observing the interference pattern of the reflected light.
- Concentricity Gage
A concentricity gage is a piece of dimensional metrology equipment known for high precision runout measurements of cylindrical objects. Precise rollers hold the object along its datum surface and indicators are used to measure the deviation of the relating feature.
- Dial Indicator
One of the most common dimensional metrology tools are dial indicators. They are frequently used in applications where linear dimensions are critical and can be set up on a surface plate or adequate fixture.
- Surface Plate
Surface plates are used as the primary (horizontal) datum for various dimensional metrology inspections. They are typically constructed of granite and are held to an extremely tight flatness tolerance depending on grade.
- Gage Block Set
Gage blocks are precision blocks of material used to set various measuring instruments. A gage block set includes an assortment of gage blocks of various sizes that can be stacked and combined together as needed.
- Go/No-Go Gage
A go/no-go gage is a dimensional metrology inspection tool that can quickly determine an object’s quality conformance by testing at the tolerance limit extremes. Conformance is determined by the part passing the “go” test and failing the “no-go” test.
- Snap Gage
A snap gage is a dimensional metrology tool that quickly determines part conformance by measuring the distance between two point contacts. There are fixed limit snap gages that are preset to the parts tolerance limits. Another type is a variable snap gage that provides variable data within the part tolerance zone.
- Thread Gage
Thread gages are a dimensional metrology go/no-go type of tool used to verify the thread form angle, pitch, and major/minor diameter.
What is metrology?
Simply put, metrology is the scientific study of measurement. Most notably, metrology provides the foundational structure of measurement that allows for the manufacturability of interchangeable parts. Metrology provides the universal definitions of the units of measure, realizes those units in practice, and maintains measurement traceability back to reference standards.
What is “dimensional metrology”?
The field of metrology broadly covers all areas of measurement. The International System of Units is compartmentalized into 7 base units: length, time, amount of substance, electric current, temperature, luminous intensity, and mass. Dimensional metrology specifically encompasses measurements of length or dimension. Also known as industrial metrology, dimensional metrology quantifies the size, shape, characteristics, and relational distances of features of interest.