The smooth and flat surface of Granite Surface Plates provides an accurate reference plane for measuring and inspecting various parts during fabrication and for the calibration of test equipment. Granite Surface Plates are used in various manufacturing plants, especially in the automotive and aviation industries, machining shops, and inspection and calibration laboratories. Surface plates are also commonly found on specific inspection equipment such as CMM’s and vision inspection systems.
A number of factors such as temperature, humidity, and vibration can affect the accuracy of the surface plate flatness, however, one of the most important and easily controlled factors is to keep the surface plate clean. Because surface plates appear thick and rugged, they’re often treated as a large table, instead of a precision piece of equipment. Since the measurements done on a surface plate can have tolerances of into the millions of an inch, even a thin layer of dirt or debris can lead to inaccurate measurements.
The greatest source of wear and tear on a surface plate is from airborne dust or debris. The dust collects on the plate and gaging surfaces and acts like sandpaper as those surfaces are rubbed together over the plate. Eventually, the surface plate wears from the abrasion and can require expensive relapping, especially when the plate is used in one specific area most of the time.
Granite is also a very porous material, so any fluids can soak into the granite if left on the surface plate. Some liquids, especially soft drinks, can contain certain acids that can dissolve the softer minerals in the surface plate and leave pitting on the surface.
The choice of cleaning solutions is important for the care of Surface Plates. The cleaner needs to be waterless and should not leave a residue or excessive moisture behind. If a water-based cleaner is used, the plate will retain the water, and this could cause rusting of metal tools and parts being used on the surface. Some cleaners will also leave a sticky residue after they dry, which will attract additional airborne dust, and actually increase wear on the surface plate, rather than decreasing it.
Professional cleaners should be used whenever possible. A Surface Place is a significant investment and should be cared for appropriately. The major dimensional test equipment manufacturers, such as Starrett and Mitutoyo make excellent Surface Plate cleaners that clean well, fully evaporate and also act as a degreaser and rust inhibitor.
The cleaner should be stored at room temperature and in an area near to the surface plate so that its use does not significantly affect the temperature stabilization of the plate.
The general rule of thumb is that if the plate is going to be used on a certain day, it should be cleaned, both at the beginning of the day and again at the end. The plate should also be cleaned immediately if the plate becomes dirty through use.
The cleaner should first be placed on the surface plate on the noticeable dirty areas or in areas that are used frequently. Use lint-free towels to wipe the surface clean. When those areas are cleaned, add additional cleaner and wipe across the entire area of the surface plate. Keep changing the towels after a few wipes to ensure the dust and debris is being removed from the surface instead of being deposited on it from dirty towels.
After the surface plate is cleaned, allow time for the plate to stabilize at the ambient temperature before being used to allow for any evaporative cooling from the cleaner. The time required will vary with the size of the surface plate. Thirty minutes to an hour should be sufficient for smaller plates.
The life and accuracy of the surface plate can be extended by placing a cover on the plate overnight or when it is not going to be used for a period of time. Both hard covers and soft covers are available. Soft covers will protect the surface plate from the accumulation of dust or debris however, a hard cover can also protect the plate against items being dropped on it and prevent the plate from becoming gouged or scratched.
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