Utilises pivoted legs to measure internal dimensions
Thickness Gauges, Snap Gauges & Caliper Gauges
What are thickness gauges and how are they used?
A thickness gauge is used to measure the thickness of a material, workpiece or feature. Traditional thickness gauges take on a similar form to a stein, in that you push down on a lever which in turn lifts up a jaw attached to a contact point. The lever is pushed until the contact point is clear of the top of the workpiece. Now, the thickness gauge can be pushed towards the workpiece and the pressure from the lever removed. A reading can now be taken using the scale which will measure depth by calculating how far the contact point has moved upwards.
In dial models with smaller scales, the dial may rotate the full 360° multiple times if the measured depth is large. The user will need to account for this by counting the number of full rotations the dial completes during the operation and add these values onto the total depth value. The advantage to using dial models with smaller scales is that these will provide a more accurate measurement (for instance, a dial gauge with a 1mm scale has a 0.001mm graduation whereas a gauge with a 10mm scale has a 0.01mm graduation).
What types of thickness gauges are there?
Thickness gauges come in many different shapes and sizes. Throat size is probably the most noticeable difference, as this determines how far the gauge can reach when being pushed onto the workpiece. Shallow thickness gauges can be used to measure edges of workpieces, whereas deeper gauges can be used to measure thickness at multiple points along a workpiece.
Application is also important when choosing a thickness gauge. For instance, if you are looking to measure tube wall thickness or the thickness of any spherical object, thickness gauges with flat anvils will not match the round bore profile and give an incorrect reading. Special tube thickness gauges are required; feature a ball-shaped contact point which will rest on the tube’s interior and provide an accurate measurement. Gauges with pointed tips are also made for fitting into small grooves and recesses.
Thickness gauges readouts are available in dial or digital variants. Digital thickness gauges will always be the most accurate type, given that the display can be up to 3 decimal places and eliminates human error when reading the scale. Dial thickness gauges are also supplied with different graduations depending on the level of accuracy required.
Another more subtle difference involves a thickness gauge’s contact point. These points are available with either ceramic or steel tips. Ceramic tips are more hard-wearing than steel.
What are snap gauges and how are they used?
Snap gauges are similar to thickness gauges in that they are used to gauge outside diameter limit measurement. Snap gauges verify or visually gauge critical measurements in production engineering. Many refer to snap gauges as a go/no-go gauge because it is used to verify that a measurement falls within a given tolerance or limit with the component being checked with an upper and lower limit anvil or dial display.
Initially, the user may use a slip gauge block to set the snap gauge at the required measurement. This will be the reference for each part to be checked. Next, the upper and lower limits are set, traditionally using two apertures on the dial face, which determines if a part passes or fails inspection. Each part is then measured by snapping the gauge over the component. If the part falls within the two apertures (e.g. if a part needs to be 10mm the upper aperture may be 10.02mm and the lower aperture 9.98mm) it passes inspection. If it falls outside the apertures, it fails.
What types of snap gauges are there?
Snap gauges can take various forms depending on the application being performed. Standard dial snap gauges are ideal for general gauging of straight or spherical workpieces and features either an in-built dial or capacity for a dial indicator to be fitted. Adjustable snap gauges feature two anvils, with one being a go gauge and the other a no-go gauge. Digital snap gauges are also available and are predominantly used for precision applications like measuring tube wall or groove thickness. One real-world application for this type of gauge is for measuring parts used in jewellery production.
Different models will also use different styles of scale. Some snap gauges will use an indicator-type dial with a linear scale, whereas others use a plus and minus format. In these models, the gauge is zeroed off with limits set at either side (left side is negative, meaning the measured object is smaller than the desired size, whereas the right side is positive, meaning the measured object is larger than the desired size). If the object falls outside either side’s tolerance, it will fail inspection.
Other features which can be found in certain snap gauge series is IP54 protection (prevents ingress of dust which causes harm and protects against liquids splashing from any angle), data output capability and manufacturer’s inspection certificates traceable to DKD.
What are caliper gauges and how are they used?
A caliper gauge is primarily used to measure the distance between two internal or external points in a workpiece, object or feature. Example uses for this type of gauge is in the measurement of bores, grooves and shafts.
Similar to thickness gauges, caliper gauges feature a lever which, when pushed, will either extend (on external caliper gauges) or contract (on internal caliper gauges) the two measuring jaws. Once the measuring jaws are securely in place, the handle is released and the jaws will then measure the distance between the two jaws.
Caliper gauges, like thickness gauges, can also be used to detect whether a measurement is within a given tolerance, therefore acting as a go/no-go gauge. On dial models this is indicated by two apertures on the dial’s surface. Digital models feature an in-built upper and lower limit setter, allowing the user to input the desired tolerance which the gauge will then check during measurement operations.
What types of caliper gauges are there?
The key difference between caliper gauge models is the type of measurement they are used for. Internal caliper gauges feature jaws which ‘stick out’ at the edge but are generally slim, with both jaws close to each other. External caliper gauges, conversely, are very wide, with jaw tips that touch each other. The gauge forms a square shape overall, with jaws that stick out significantly at each side.
As previously mentioned, caliper gauges are supplied with either dial or digital readouts. Digital caliper gauges will always be the most accurate type, given that the display can be up to 3 decimal places and eliminates human error when reading the scale. Dial caliper gauges are also supplied with different graduations depending on the level of accuracy required.
Other features that some caliper gauge models have include data output, rotatable display (up to 320°) and carbide measuring tips. Digital caliper gauges can also convert measurements to imperial sizes, switch between absolute (whole number) and incremental measurement and measure direction change.
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