Use and Care Of Granite Surface Plates – Maintenance Tips
Cleaning and moisture:
One of the first principles of use and care of Granite Surface Plates is that you should clean the plate thoroughly. It is important that you dry it after cleaning for 5 hours before testing for tolerance. The choice of cleaning solution is important. If a volatile solvent is used (acetone, lacquer thinner or alcohol), the evaporation will chill the surface and distort it. So, it is necessary to allow the plate to return to normal temperature before using it to avoid measurement error. In the case of a water-based cleaner, there will be some evaporative chilling. The plate will also retain the water, and this could cause rusting of metal parts which are in contact with the surface. Some cleaners will also leave a sticky residue after they dry. This will attract airborne dust, and actually increase wear, rather than decrease it.
A surface plate should be under constant temperature and with less than 50% relative humidity. Avoid direct sunlight or sudden draughts.
Clean the surface plate twice a day, before and after work. When a plate is soiled with oily or sticky fluids, it must be cleaned immediately. The plate should be supported firmly and levelled. Stands should be located on a stable foundation.
Scratches and Nicks:
Burrs due to scratches and nicks on granite plates should be removed with flat silicon carbide stone. Any hump, which forms on a damaged surface, raises fractured material at the edges of the area of damage.
The surface plate is a datum, and you should protect it against damage. Frequently wipe clean the top from dust and other particles. When you take measurements, spread a wiping cloth on the plate to place small tools and gauge blocks.
Cuts on the surface are a common sign of damage. Always cover the top when the plate is not in use. GMT can supply finished wooden covers to protect the plate’s surface. Abrasive dust is usually the greatest source of wear and tear on a plate. It tends to embed in workpieces and the contact surfaces of gauges. So it is equally important to clean the workpiece and the guage thoroughly before a measurement. They too should be allowed to normalise to room temperature before proceeding with the measurement.
It is important to learn the use and care of Granite Surface Plates. Take care to avoid over-load on the plate. Wherever possible, distribute the load on a surface plate. Also, avoid setting food or soft drinks on the plate since many soft drinks contain either carbonic or phosphoric acid, which can dissolve the softer minerals and leave small pits in the surface.
Rotation of plate:
When a specific work surface area receives hard usage, we suggest that you rotate the plate 180° periodically to produce uniform wear and increase life. The production of a contour map attained during calibration is particularly helpful in locating the worn parts of the plate.
We recommend periodic recalibration of granite surface plates in the use and care of Granite Surface Plates. This is to determine resurfacing or replacement needs. The interval between calibration will vary with the grade of plate and usage. You also have to consider wear resistance and with the conditions and frequency of use. Surface plates in the manufacturing department require recalibration every six months, whereas plates in the laboratory require recalibration every year. Frequent monitoring of the work surface by scanning it with the repeat reading gauge is important. When the results differ from the grade value, as mentioned in the standard, then it should be re-calibrated.
The instruments for calibrating surface plate flatness are autocollimator, electronic level and laser interferometer. Also, you can use master straightedge with a travelling indicator or with beam gauge, linear beam and detector and in-line flatness gauge.
Downgrading, resurfacing or replacement levels:
During recalibration, the surface plates that deviate from work surface flatness tolerance have to be downgraded, resurfaced or replaced. This applies to plates which show repeat readings that exceed the in-house requirements. Plates which have objectionable scratches and nicks in the work area also have to be resurfaced or replaced.
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