ASME B89.3.7:2013 pdf download

ASME B89.3.7:2013 pdf download.Granite Surface Plates
1 GENERAL
1.1 Scope This Standard covers igneous rock (granite) plates for use in high accuracy locating, layout, and inspection work. It encompasses new certification, recertification in the field, and recertification after resurfacing. In gen- eral, the standard covers any size granite surface plate. Information for the sizes in common use is presented in tabular form. 1.2 Classification: Styles and Grades Surface plates shall be of the following styles and grades: (a) Styles (shapes) • Rectangular, no ledge (see Fig. 2) • Rectangular, 2 ledge, either direction (see Fig. 3) • Rectangular, 4 ledge (see Fig. 4) • Round, no ledge (see Fig. 5) (b) Grades • AA • A • B
2 DEFINITIONS
bow: the condition of a surface plate where the middle of the plate is higher or lower than the two ends. F.I.M.: Full Indicator Movement. flatness: the condition of a surface or derived median plane having all elements in one plane. grade: the classification of a surface plate according to the flatness and repeat reading tolerance of the work surface. (This Standard covers three grades: AA, A, and B.) inserts: typically made of metal (usually stainless steel, to prevent rusting) and are “plugs,” usually predrilled and tapped to various thread diameters and pitches, and are epoxied into a granite surface plate. They can also be furnished as a “solid” insert — no predrilling or tapping. Threaded inserts allow for hold-down capa- bilities and fixturing on a granite surface plate. ledge: an undercut made along the sides or across the ends (or both) of a surface plate. repeat reading: a measure of flatness over localized areas ofa surface plate. This measure is usuallyobtained using a repeat reading gage (see following definition) that measures height variation of the surface plate from a reference established by the base of the repeat reading gage. The range of readings taken with a repeat reading gage represents local deviation from flatness over the area sampled. repeat reading gage: a gage used to obtain repeat readings (see Fig. I-3). This instrument estimates the ability to reproduce a measurement of a fixed height at any place on the surface plate. The repeat reading gage is sensitive to short wavelength variations in flatness when readings are taken over small intervals of movement of its base. twist: the condition of a surface plate where the plate takes on the shape of a surface whose ends have been turned in opposite directions (e.g., like the shape of a propeller). The four corners of plates having this condi- tiondo notlie withinthe same plane. The lines character- izing opposite ends of a surface plate that exhibits twist have some relative angle between them (see Fig. 1).
4 GENERAL REQUIREMENTS
4.1 Materials Surface plates covered by this Standard shall be made from fine or medium grained igneous rock, e.g., material such as biotite granite, biotite hornblende, diabase, hypersthene gabbro, muscovite-biotite, and muscovite biotite/granite-gneiss, etc. The material shall be free of cracks or other defects that may affect the serviceability of the surface plate. Other granites are acceptable pro- vided they meet the requirements ofthis Standard. Refer to Table A-1 for material properties. 4.2 Cracks and Color Streaks Cracks are cause for rejection. Color streaks have no effect on the serviceability of the granite and are acceptable. 4.2.1 Style. Surface plates covered by this Standard shall be of the four styles illustrated in Figs. 2 through 5. 4.2.2 Size. Surface plates covered by this Standard shall be any size. The most common sizes are listed in Table 1. 4.2.3 Thickness and Stiffness. The surface plate shall have a thickness capable of supporting a total nor- mal load equal to 240 kg/m 2 (50 lb/ft 2 ) of surface plate area, loaded in the center of the plate, without deflecting the plate along a diagonal or diameter more than one-half the flatness tolerance (see Nonmandatory Appendix B). 4.2.4 Clamping Ledges. See Fig. 3. 4.2.4.1 Clamping ledges on surface plates under 150 mm (6 in.) thick shall not be less than 40% of the surface plate thickness, in thickness, X, and the over- hang, Y, shall be approximately one-fourth ofthe surface plate thickness.