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Caliper

What is a caliper?

A caliper is a versatile and precise hand measuring instrument that is widely used in various industries, such as metalworking, woodworking, science, and medicine. Calipers allow the measurement of highly accurate external and internal distances as well as depths. This tool is especially important in machining, where accuracy and quality are paramount.

The Importance of Calipers in Machining

In machine shops and machining facilities, accuracy and quality of work are essential. The caliper is a basic measuring tool used daily to measure parts. Every machinist's workstation should have a reliable caliper due to its accuracy and versatility. Calipers are used to measure, among other things, external diameters, internal diameters, depths, shoulder lengths, and groove widths.

A caliper allows the measurement of precise dimensions, provided it's in good condition and used correctly. This is particularly important in machining, where even small measurement errors can result in faulty outcomes and quality issues. Using a caliper helps ensure that machined parts meet precise tolerances and quality standards.

Guidelines for Using a Caliper

  • Measuring: Calipers should be used exclusively for measuring. Do not use them as scribers or for any other purpose, as this can damage the tool and reduce its accuracy.
  • Inspection: The condition of the caliper can be checked by bringing the jaws together; the scale should read exactly zero, and no light should be visible between the jaws. This check should be performed regularly and always before taking measurements.

Basic Structure and Operation of a Caliper

A caliper consists of several key components. Below are the parts of an analog caliper with a vernier scale:

  • Body: The main part of the caliper to which all other components are attached.
  • Slider: The movable part that allows the moving jaw to slide and the measurement to be read.
  • Fixed Jaw: The stationary jaw attached to the body.
  • Moving Jaw: The jaw that moves with the slider and enables measurements to be taken across objects.
  • Inside Measuring Tips: Used for measuring internal dimensions, such as holes or grooves.
  • Depth Measuring Blade: A rod for measuring depths, extending from the end of the caliper.
  • Main Scale: The primary scale showing whole millimeters.
  • Vernier Scale: The more precise scale that allows readings to the nearest tenth of a millimeter (0.1 mm).
  • Locking Screw: The screw used to lock the scale in place after measuring, allowing easy reading of the measurement value.

Digital Calipers

Digital calipers follow the same basic structure as analog ones, but the main and vernier scales are replaced by a digital display. This allows for more precise readings, often to hundredths of a millimeter (0.01 mm). Digital calipers provide several advantages, such as clearer readability and the ability to wirelessly transfer measurements to, for example, Excel-based measurement logs.

Although calipers are typically read to two decimal places in millimeters, their measurement accuracy is not sufficient for reliably measuring tolerances finer than this. In such cases, measurements should be taken with a micrometer.

Special Calipers

There are various special calipers designed for particular measurement tasks:

  • Depth Caliper: Specifically for measuring depths.
  • Thread Caliper: For measuring threads.
  • Groove Caliper: For measuring groove widths.
  • Large Machine Shop Calipers: Designed for measuring large parts, they may have a measurement range even over 2000 mm.
  • Jaw Options: Different jaw types are available for various applications, such as measuring pipe wall thicknesses or the diameters of internal grooves.

Maintenance and Care

Proper maintenance of the caliper is important to ensure accuracy:

  • Cleaning: Wipe the jaws, sliding surfaces, and tips clean of dust and oil before and after use with a soft, dry cloth.
  • Oiling: Clean the caliper of oil and water after use and apply a thin layer of protective oil.
  • Storage: Avoid storing in direct sunlight, high temperatures, or humid environments. Store the jaws slightly open. Calipers should not be kept in a pocket, but only in their original case.
  • Avoiding Damage: Don't use the caliper for anything other than measuring and handle it carefully to keep the tips and jaws intact.

Minimizing Measurement Errors

Measurement errors can be caused by various factors:

  • Measuring Force: Excessive force can distort measurement results. Use only the necessary force.
  • Temperature Variations: The caliper body and the measured part may expand or contract differently at different temperatures, affecting measurement accuracy. The official measurement temperature is 20 °C, and this should be considered to avoid errors due to thermal expansion.
  • Parallax Error: On an analog caliper, always read the vernier scale straight on.
  • Misalignment: Internal tips and jaws must be positioned at a right angle to the workpiece.

Summary

The caliper is an essential measuring tool for machinists, playing a central role in the daily operations of machine shops. It delivers accuracy and reliability in numerous measurement tasks, and its use is crucial for achieving high quality and precise tolerances. With proper maintenance and correct use, a caliper will remain accurate and reliable for a long time, making it an indispensable tool at every machinist's workstation.