Technical Informa tion Certified Accuracy Before shipment, each surface plate must pass a critical final inspection to prove that its entire surface is within the specified tolerance. The final inspection is done with an autocollimator in a controlled environment. This instrument is checked and certified against standards traceable to the U.S. National Institute of Standards and Technology (NIST). The instrument's certification is on file at the Starrett Tru- Stone Technologies Division in Waite Park, MN. All shipments of Starrett precision granite products include a calibration certificate which verifies traceability to NIST as well as certifying that the inspection requirements of U.S. MIL-I-45208A and Federal Spec. GGG-P-463c and ASME B89.3.7 2013 have been met. Periodic Inspection Every surface plate in use should be frequently inspected, especially when used in shop conditions where abrasion is common. An effective inspection program should include regular checks with an autocollimator. If tolerance variations are excessive, the plate can be transferred to work involving less accuracy or it can be resurfaced to restore its original level of accuracy. Resurfacing Services Resurfacing for Starrett and other brands of granite surface plates are available in our plant or yours. Design Assist ance Starrett engineers will provide prompt assistance with any problem related to surface plate design,installation or use.Our staff is available to assist in your design of larger OEM projects. To get the best service and value from any granite plate, contact Starrett Tru-Stone. Accuracy Granite Surface Plates are manufactured in three grades of accuracy: • Grade AA – Laboratory Grade This is typically specified for precision operations in constant temperature gaging rooms and metrology departments. • Grade A – Inspection Grade This is typically specified for general work in quality control. • Grade B – Toolroom Grade This is typically specified for production checking work throughout the shop. Unila teral Fla tness Tolerance Overall flatness tolerance is based on unilateral measurement. All points on the work surface shall be contained between two parallel planes separated at a distance no greater than the amount specified for each particular grade and size as shown in our listings. Repea t Reading Tolerance Repeat reading tolerance is easily checked with a Repeat Reading Gage. This gage detects local areas, not overall flatness. In addition to the overall flatness tolerance referred to above, Starrett provides repeat reading tolerances as follows: Inspecting a granite plate with an autocollimator Diagonal Inches (mm) Full Indicator Movement (F.I.M.) in Microinches and (Microns) Obtained Grade AA Grade A Grade B Through 30" (750) 35 (.9) 60 (1.5) 110 (2.8) When Not Specified Over 30-60" (750-1500) 45 (1.1) 70 (1.8) 120 (3) Over 60-90" (1500-2250) 60 (1.5) 80 (2) 160 (4) Over 90-120" (2250-3000) 75 (1.9) 100 (2.5) 200 (5) Over 120-150" (3000-3800) 90 (2.3) 120 (3) 240 (6) Over 150" (3800) 100 (2.5) 140 (3.6) 280 (7) All Sizes 25 (.6) 50 (1.3) 100 (2.5) When Specified A repeat reading gage detects minute variations of the surface within the unilateral flatness tolerance of the whole surface. 411 G ranite S urface P roducts