A Height Gage in a CMM’s Skin

An electronic height gage is the tool of choice for the versatility of a wide range of parts — whether first-part qualification, incoming inspection or even a series of parts — due to its versatility and direct-reading measurement capabilities. In fact, many digital height gages can be thought of as single-axis CMMs or even two-axis versions when using the built-in functions to measure straightness or squareness.

As with a CMM, today’s electronic height gages are computer-based, touchscreen-operated systems that enable automated measuring routines, error correction and multiple probe offsets, and have the ability to easily create and run serial part programs.

The typical size for height gages ranges between 350 and 1,000 millimeters, but they are available in sizes up to 1,800 millimeters. With extensions, even more capacity is possible. Height gages by themselves cannot make a measurement without a reference. The reference is the surface plate — the foundation of all precision.

Once the height gage is set in place, two critical references must be established. The first is the zero reference for the measuring system. With automated height gages, this is done whenever the gage is turned on; the gage will automatically move down to touch the surface to set its reference point.

The other important reference is the correction for probe ball diameter. If a height gage is used only for length measurements taken with the probe moving down, then probe diameter is not important. The contact point of the probe will be the same as in zeroing. However, if grooves, diameters or hole locations are being measured, or if any measurements are taken with the probe moving upwards, then the probe ball diameter must be known and taken into account.

With new motorized digital versions, measurement is an easy keystroke of an icon on a large touchscreen. When ready to make a measurement, say a height in reference to the zero point, slide the measuring carriage up over the part and press the height measurement icon, approaching from the top. The motorized drive will bring the contact to the surface, and the measurement is completed and displayed. However, with the modern height gage, this is only the beginning of its measuring capabilities. There are dedicated icons for most common measuring functions, such as up/down lengths from the reference, ODs, IDs, center distance, flatness and even taper measurements. If the height gage has 2D functions, straightness and perpendicularity are the touch of an icon away.

As measurements are made, they are stored internally, and even more relationships between the stored data, such as center distance and other relationships, can be made without having to actually measure the part. The measuring process will also act as a basis for a part program. Since every measurement and routine is stored on the gage, this past measurement history can be used as a new part program. Thus, when the part comes along again or there are a series of similar parts to be measured, this routine becomes the part program for repeating the measuring process.

Besides using the measurement sequence as the basis for creating the part program, the measurement results can be stored or saved in a number of different ways. The raw results can be saved as a file or stored on a USB stick, stored in a preformatted and customized PDF file, or transferred to the network or cloud via cable or wirelessly for long-term storage and analysis.

In summary, today’s height gages are feature-packed and high-performance measuring systems. In reality, they can be thought of as single-axis CMMs. Considering that they implement canned measuring modes, can store part programs, can use different probes with various contact configurations and diameters and have the ability to store/print gaging results, they really do have all the same CMM capabilities as a single-axis. When used on a good surface reference, electronic height gages can offer substantial benefits in terms of time and productivity savings. High-quality measurements can now be made on the shop floor or as part of a receiving inspection area at a price that offers high value for the results provided.