Is Precision Granite an accredited lab?
Yes. We are accredited through A2LA, ISO-IEC-17025-2005.
How often should I have my granite plate calibrated?
This is perhaps the most difficult question due to many different factors. Some of the many factors that go into this determination are: amount of use, type of use, type of granite, and operator awareness to name just a few. Building a history over time and documenting the amount of wear is what we recommend. Most customers will request at least a yearly inspection and calibration.
If the surface of my granite plate is too rough can I flip the granite plate?
No. The bottom of granite plates are not precision surfaces.
How can I keep my instruments sliding smoothly across my granite plate?
Cleaning a granite plate will greatly aid with this problem. There are many good cleaners available today. We recommend trying different ones to see which works best for you.
Does my granite plate need to be level to be flat?
No. Most granite plates in most shops are not level. However they can still be calibrated and flat.
Does Precision Granite go onsite to locations and companies?
Yes. Precision Granite is fully equipped for complete onsite services. Some equipment can only be serviced onsite. At the time your job is quoted, it will be determined what equipment and gauges will be calibrated onsite or in lab.
How are Granite Surface Plates checked for flatness – it looks good to the naked eye?
Repeat Measurements and Flatness
Both flatness and repeat measurements are critical to ensure a precision surface. Flatness can be considered as all points on the surface being contained within two parallel planes, the base plane and the roof plane. The measurement of distance between the planes is the overall flatness of the surface. This flatness measurement commonly carries a tolerance and may include a grade designation.
The flatness tolerances for three standard grades are defined in the federal specification as determined by the following formula:
Laboratory Grade AA = (40 + diagonal² / 25) x 0.000001 inch (unilateral)
Inspection Grade A = Laboratory Grade AA x 2
Tool Room Grade B = Laboratory Grade AA x 4
In addition to flatness, repeatability must be ensured. A repeat measurement is a measurement of local flatness areas. It is a measurement taken anywhere on the surface of a plate that will repeat within the stated tolerance. Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.
To ensure a surface plate meets both the flatness and repeat measurement specifications, manufacturers of granite surface plates should use Federal Specification GGG-P-463c as a basis for their specifications. This standard addresses repeat measurement accuracy, material properties of surface plate granites, surface finish, support point location, stiffness, acceptable methods of inspection and installation of threaded inserts.