Metrology Instruments

Surface Plates

The Care And Use of Surface Tables And Plates

British Standard Reference : BS 817 : 1988

1. A Surface Plate is a datum and should be protected against damage. The top should be frequently wiped clean from dust and other particles. When measurements are being made, a cloth should be spread on the Surface Plate to receive small tools and gauges. When the Surface Plate is not in use the top should always be kept covered.

2. A grade '0' or grade '1' Surface Plate should be located in a circulating atmosphere under constant temperature control. Accordingly, it should be kept clear of direct sunlight or sudden draughts, in particular it is important that these should not cause a vertical gradient of temperature such that the top and underside of the Surface Plate are at difference temperatures.

3. Stands should be located on a stable foundation. The Surface Plate should be supported firmly and levelled.

4. Care should be taken that, wherever possible, the load on a Surface Plate is distributed over the working surface.

5. Point contact should not be made with scraped or machined Surface Plates because of the high proportion of low, unrepresentative areas of the working surfaces. Contact should be made through an intermediate Gauge Block, preferably not more than 10mm in length, or a distance piece of similar precision and surface area.

6. Use should be made of the full available area of the working surface and not concentrated on any one area.

7. A common form of damage to Cast Iron Surface Plates is burrs on the working surface, the excess metal may be stoned away by attention confined to the burr. This operation should be followed by thoroughly cleaning away any abrasive dust. If the Surface Plate is not required for some days, the surface should be coated with a corrosion preventative such as petroleum jelly.

Rusting is a sign of neglect and misuse. Its effect can be reduced by frequently wiping the top when in use and by occasionally gently rubbing with another Surface Plate using a paste of a little jewellers rouge and paraffin as a lubricant.

8. A common form of damage to Granite Surface Plates is cuts in the working surface, these can be minimised only by care in the use of the Surface Plates.

9. Cleaning of Granite Surface Plates should be performed with the use of the specialised compounds available from the manufacturers.

10. A border zone of 10mm on the edges of Surface Plates/Surface Tables should be avoided when taking measurements.

11. Never use a surface plate/surface table that has not been calibrated, if in doubt consult an appropriate authority.