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1. Why granite? Is it better than steel or cast iron for precision surfaces?

The answer is 'yes' for almost every application. The advantages of granite include: No rust or corrosion, almost immune to warping, no compensating hump when nicked, longer wear life, smoother action, greater precision, virtually non-magnetic, low co-efficient of thermal expansion, and low maintenance cost.


2. How should my surface plate be supported? Does it need to be level?

A surface plate should be supported at 3 points, ideally located 20% of the length in from the ends of the plate. Two supports should be located 20% of the width in from the long sides, and the remaining support should be centered. Only 3 points can rest solidly on anything but a precision surface.

The plate should be supported at these points during production, and it should be supported only at these three points while in use. Attempting to support the plate at more than three points will cause the plate to receive its support from various combinations of three points, which will not be the same 3 points on which it was supported during production. This will introduce errors as the plate deflects to conform to the new support arrangement.

If the plate is properly supported, precise leveling is only necessary if your application calls for it. Leveling is not necessary to maintain the accuracy of a properly supported plate.

3. Why do the calibrations performed on my surface plate seem to vary?


There are several possible causes for variations between calibrations:

1)  The surface was washed with a hot or cold solution prior to calibration, and was not allowed sufficient time to normalize.

2)  The plate is improperly supported.

3)  Temperature change.

4)  Drafts.

5)  Direct sunlight or other radiant heat on the surface of the plate. Be sure that overhead lighting is not heating the surface.

6)  Variations in the vertical temperature gradient between winter and summer. (If at all possible, know the vertical gradient temperature at the time the calibration is performed.)

7)  Insufficient normalizing time after shipment.

8)  Improper use of inspection equipment or use of non-calibrated equipment.

9)  Surface change resulting from wear.



4. I need fastening points on my surface plate. Can threaded holes be added to a surface plate?

Yes. Steel inserts with the desired thread (English or metric) can be epoxy bonded into the plate at the desired locations. We use CNC machines to provide the tightest insert locations within +/- 0.2mm. Other options include steel T-Bars and dovetail slots machined directly into the granite.


5. How can I reduce wear, and extend the life of my surface plate?


First, it is important to keep the plate clean. Airborne abrasive dust is usually the greatest source of wear and tear on a plate, as it tends to embed in work pieces and the contact surfaces of gages. Second, cover your plate to protect it from dust and damage. Wear life can be extended by covering the plate when not in use, by rotating the plate periodically so that a single area does not receive excessive use, and by replacing steel contact pads on gauging with carbide pads. Also, avoid putting food or soft drinks on the plate. Note that many soft drinks contain either carbonic or phosphoric acid, which can dissolve the softer minerals and leave small pits in the surface.