Machinery's Handbook, 31st Edition
V-BLOCK CLASSIFICATION 733 Classification.— The Federal Specification GGG-V-191D 1971 “V Blocks and Clamps” was developed to provide the acceptable criteria for items to be purchased under contract by the US Government or Department of Defense. This specification has been superseded by Federal Specification A-A-51150B and since canceled. However, these and related standards are still referenced by many manufacturers of precision V-blocks and were the initial guidelines for the manufacturing and specification of the tool. Federal Specification Coverage: This specification covers only the types, styles and grades generally purchased by the Federal Government, and does not include all types, styles, and grades which are commercially available. Type, Style, and Grade Type I – Single V-Groove ( page 735 ) Style 2: Double level clamping Style 3: Reversible clamping yoke Style 4: Magnetic clamping (mild steel and brass laminated) Style 5: Ribbed, without clamping Style 6: Plain without clamping Grades: Grade A: Steel (alloy); Grade B: Mild Steel (and brass laminated for style 4); and Grade C: Cast Steel. Type II – Double V-Groove ( page 738 ) Style 1: Single level clamping Grades: Grade A: Steel (alloy); and Grade B: Cast Iron (class 40 iron). Type III – Quadruple V-Groove ( page 739 ) Style 1: Single level clamping Grades: Grade A: Steel (alloy); and Grade B: Cast Iron (class 40 iron). Type IV – Combination, Top and End V-Grooves ( page 741 ) Style 1: Single level clamping Grades: Grade A: Steel (alloy) Material.— Note: Grade and surface finish specifications are a representation of all gov erning standards in use today. Grade A Blocks: Grade A blocks shall be steel or steel alloy and shall have a surface hardness of 58 to 65 RC on the Rockwell C scale. Grade B Blocks: Grade B blocks shall be a good quality mild steel, free from porosity and other injurious defects and have a surface hardness of 40 to 45 on the Rockwell C scale. Grade C Blocks: Grade C blocks shall be a good quality cast steel free of porosity or other injurious defects and shall have a surface hardness of 150 to 180 BHN (Brinell Hardness Number). Precision Granite Blocks: Precision granite V-blocks shall be made from a close grained uniform texture granite free from flaws or fissures and inclusions of softer material. Gran ite V-blocks shall adhere to either Grade A or B accuracy. Grade A and matched sets are to be provided in a protective case. Finished Surfaces: Surfaces of the V-grooves, tops sides, bottom, V-groove relief slots, and clamp engaging grooves shall have finished surfaces measured in micrometers arithmetical average (A.A.) or roughness average (Ra) in accordance with ANSI/ASME B46.1-2009. All other surfaces shall be finished in accordance with normal manufac turer’s standard commercial practice. Surface Finish, Grades A and B, Style 4, Blocks: Surface of V-groove relief slots and clamp engaging grooves (when applicable) on blocks shall have a surface roughness not greater than 125 µ in (3.175 µ m). All other finished surfaces shall have a surface roughness not greater than 32 µ in (0.81 µ m) Ra.
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