Checking Measuring Instrument Accuracy with Slip Gauges

Accurate measurement is crucial in many fields, especially engineering and manufacturing. Tools like micrometers, callipers, and dial indicators are commonly used, but their accuracy can drift over time or with use. Regularly checking and calibrating these instruments ensures reliable measurements.

Why Slip Gauges are Used for Calibration

The question asks how the accuracy of micrometers, callipers, and dial indicators can be checked. Among the options provided, slip gauges are specifically designed for this purpose. Slip gauges, also known as gauge blocks, are precision ground and lapped steel or ceramic blocks manufactured to extremely tight tolerances.

• They come in sets of various sizes.
• Blocks can be 'wrung' together to create precise combined lengths.
• These combined lengths serve as highly accurate standards.

When checking a micrometer or calliper, a slip gauge (or combination of slip gauges) is used to create a known, precise distance. The reading on the instrument is then compared to the known size of the slip gauge. If the instrument reading matches the slip gauge size, it is accurate at that specific measurement. This process is repeated at different points along the instrument's range.

For a dial indicator, slip gauges can be used in conjunction with a surface plate and stand to check the indicator's linearity and accuracy over its range of travel.

Understanding Other Gauge Types

Let's look at why the other options are not suitable for checking the general accuracy of micrometers, callipers, and dial indicators:

• Feeler Gauge: A feeler gauge consists of a set of thin metal blades of graduated thickness. It is used to measure the width of small gaps or clearances, such as valve clearances in an engine. It provides a direct measurement of a specific gap but cannot be used to calibrate the linear scale of a micrometer or calliper.
• Ring Gauge: A ring gauge is a cylindrical ring used to check the external diameter of a cylindrical part. It is a GO/NO-GO gauge or a limit gauge, checking if a part's diameter is within specified tolerances. It checks a specific dimension of a workpiece, not the calibration of a measuring instrument.
• Plug Gauge: A plug gauge is a cylindrical plug used to check the internal diameter (a hole) of a part. Like a ring gauge, it is often a GO/NO-GO gauge. It checks a specific dimension of a workpiece, not the calibration of a measuring instrument.

Therefore, only the slip gauge provides the necessary precision and versatility to act as a standard for checking the accuracy of linear measuring instruments like micrometers, callipers, and dial indicators across their measurement range.

Based on the function of each gauge type, the slip gauge is the appropriate tool for checking the accuracy of the specified measuring instruments.

Revision Table: Key Measurement Tools

Additional Information on Slip Gauges for Calibration

Slip gauges are fundamental standards in metrology. They are typically made from hardened steel, ceramic, or tungsten carbide. They are manufactured to different grades depending on the required accuracy:

• Grade K: Calibration grade, highest accuracy, used for calibrating other slip gauges.
• Grade 00: Inspection grade, very high accuracy, used in metrology labs.
• Grade 0: Inspection grade, high accuracy, used in inspection departments.
• Grade 1: Workshop grade, used for setting up machines and checking gauges.
• Grade 2: Workshop grade, lower accuracy, used for less precise checks.

When checking instruments like micrometers or callipers, Grade 0 or Grade 1 slip gauges are commonly used. The technique of 'wringing' is used to combine slip gauges, which involves sliding them together to create a strong bond and precise combined length due to molecular adhesion and atmospheric pressure.

Regular calibration using traceable standards like slip gauges is essential for maintaining quality control in manufacturing and engineering processes.