Snap gauges, also called gap gauges, are metrology tools that are used to gauge the diameter or thickness of a part or material. These tools are versatile and are designed to provide a quick go/no-go decision on cylinders, shafts, grooves, and other similar parts and features in machining operations. Functionally, snap gauges perform assessments on the outside diameters of parts, similar to other tools and measurement instruments such as ring gauges and thickness gauges. Snap gauges can be used for checking dimensions on both cylindrical and non-cylindrical parts whereas ring gauges are for cylindrical parts only. As a tool for inspection and quality control, the purpose of a snap gauge is to provide a rapid means of determining if the outside dimensions of the part are within its specified tolerances. It is a gauging tool principally, and as such is designed to perform an assessment of whether the part meets its dimensional specification without directly providing a measurement of the actual value of that dimension.
Advantages of Snap Gauging:
- Speed – more parts can be checked using gauging
- Less dependence on the skill level of the tool user
- Economy – gauges are usually less expensive than measuring instruments
Types of Snap Gauging:
(1) Fixed limit Snap Gauges –
Fixed limit snap gauges are designed to assess dimensional tolerance for a single value of the dimensional parameter.
(2) Adjustable limit Snap Gauges-
Adjustable limit Snap Gauges feature a locking mechanism for the position of the anvils to allow the dimension parameter to be adjusted to different values as the metrology needs change.
(3) Combined limit Snap Gauges –
Combined limit snap gauges have the go and no-go dimensional gauges on the same side of the tool, with the go gauge on the outer edge and the no-go gauge interior relative to the go gauge. These are also called progressive snap gauges since the assessment process takes place sequentially with the go gauge contacting the workpiece initially before the no-go gauge makes contact.
(4) Double-ended Snap Gauges-
These types of snap gauges have a double C frame with the go gauge on one end or side and the no-go gauge on the other side rather than nested within a single set of jaws as with the combined limit gauge.
(5) Dial Snap Gauges-
Dial Snap Gauge, also known as snap indicator gauges; add a display to the tool (either analog or digital) that provides an indication of the amount of deviation from the nominal value exhibited by the part being gauged. The deviation is a plus o
(6) Thread Snap Gauges-
Thread Snap Gauges sometimes referred to as thread calipers, these tools are used to check the conditions and acceptability of externally threaded parts rather than smooth finished surfaces as with plain snap gauges. These conditions include out-of-roundness, the radius at root oversize, a malformed major diameter, excess angle error, or pitch error.
Material choices for snap gauges are typically tool steel, with options for carbide on the measuring faces to provide for wear protection.