What is a granite surface plate used for?
JASH Granite Surface Plates are used for precision gauging, inspection, layout and marking purposes. They are preferred by Precision Tool Rooms, Engineering Industries and Research Laboratories because of their following outstanding advantages.
What are the grades of granite surface plates?
Manufacturers use three standard grades of flatness defined by the federal specification: Laboratory grade AA: (40 + diagonal [in inches] of surface plate squared/25) x 0.000001 in. Inspection grade A: Laboratory Grade AA x 2. Tool room grade B: Laboratory Grade AA x 4.
How do you support a granite surface plate?
A) 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.
Can a granite surface plate warp?
Surface Plates can experience chipping, warping, and just plain wear, so they must be calibrated regularly. Often, the wear will be localized due to a particular tool, such as a height gauge, being used in the same place constantly. Surface Plates should also be kept as clean as possible.
Which surface plate is more accurate?
The highest accuracy plates are called Grade AA, and they are often found in calibration laboratories. Grade B plates are the lowest accuracy plates, and they might be found on shop floors. The middle grade plates, Grade A, are often used in inspection areas.
What is the accuracy of surface plate?
They have been proven very valuable to record long term effects of surface plates. Reliable measurements with an accuracy of 0.1 μm/m demonstrate the capabilities of the method.
What is the best granite for surface plate?
The most commonly used type of granite for surface plates is black granite, however quartz-containing granite, known as pink granite, may also be used. Black granite, also known as diabase, is prized for its capability to bear heavy loads.
Why granite is the most popular material for surface plates?
Granite is considered to be the best material for a surface plate due to its surface hardness, low thermal expansion, no rust or corrosion, little warping, and long wear life attributes. These attributes result in very accurate, stable and precise measurements.
How is a surface plate calibrated?
Calibration is done by checking conformance of the surface plate to the two different tolerance values. If necessary, adjustments to the surface plate flatness – typically onsite re-lapping – can be done by those with the required skills and tools.
How flat is a granite surface plate?
This granite reference plate is used to measure objects, mostly in metal work, for flatness and squareness. It is flat to within 3 µm (1 µm = 0.001 mm) measured from a corner across the surface.
Which surface plate has high accuracy?
3.7 defines standardized tolerance grades for surface plates. The highest accuracy plates are called Grade AA, and they are often found in calibration laboratories. Grade B plates are the lowest accuracy plates, and they might be found on shop floors.