## Dimensional Measurements## Angular Measurements
Theodore D. Doiron
back to top | back to index of dimensional measurements ## Angle Gage Blocks (14010C-14011C)Angle blocks are measured in an angle comparator system consisting of a special chamber and two autocollimators. The blocks are placed in the chamber to minimize air currents and stray light effects. The test blocks are compared to NIST master angle blocks following an intercomparison method to eliminate thermal drift. Measurements are made in both top up and bottom up positions. Check standard blocks are measured during the procedure as well as for process control. Standard size block sets include (1-, 3-, 5-, 20-, and 30-) sizes; (1", 3", 5", 20", and 30") sizes; and 1°, 3°, 5°, 15°, 30°, and 45° sizes. The expanded uncertainty for this calibration is approximately 0.18" for ideal blocks. However, this value varies with the condition and geometry of the test block gaging surfaces. Customer angle blocks with poor gaging surfaces blocks can have uncertainties as high as 0.3" to 0.4". Angle blocks with dimensions other than standard (1 inch by 2 inch (2.54 cm by 5.08 cm) in measuring faces) require different measurement methods and generally result in higher uncertainties. All angle blocks submitted for calibration should be in substantially new block condition, and each marked with an identification number. In shipping angle blocks, the same care exercised in gage block shipment should be used. back to top | back to index of dimensional measurements ## Special Tests of Optical Polygons (14020S)NIST provides special tests for optical polygons. Optical polygons are calibrated using an indexing table stack, an autocollimator and circle closure measurement techniques. Polygons with nominally equal angles between faces are normally measured by closure. The expanded uncertainty for this calibration is approximately 0.14"; however, this value varies with the condition and geometry of the polygon faces. The technical contact must be consulted before this special test is requested. back to top | back to index of dimensional measurements ## Special Tests of Rotary and Indexing Tables (14030S-14031S)NIST provides special tests for rotary and indexing tables. Indexing tables (limited, fixed-increment, high repeatability). These tables and rotary tables (continuous increment, low repeatability) are calibrated using an autocollimator and reflecting target, an indexing table stack, and circle closure techniques. The standard set of angular increments is every 30°. Additionally, every 5° of the first 30° interval, and every 1° of the first 5° interval can be measured. Check standard indexing tables are used for process control during the measurement procedure. Indexing tables must be less than a maximum 254 mm (10 inch) in diameter. The expanded uncertainty for this calibration is approximately 0.14", however, this value varies with the locking mechanism repeatability and the scheme of angles chosen to be measured. The technical contact must be consulted before this special test is requested. back to top | back to index of dimensional measurements ## Special Tests of Optical Wedges (14040S-14041S)NIST provides special tests to calibrate optical wedges. Optical wedges are calibrated using an autocollimator, a reflecting target, the test wedge and a repeated reversal measurement series. Fixed angle and adjustable wedges can be calibrated. The wedge is inserted between the autocollimator and reflecting target and measured. The wedge is removed, rotated 180° about the same base, reinserted and measured. In this reversal technique the difference in the two measurements is equal to twice the actual angle. Check standard wedges are measured for process control. The expanded uncertainty for this calibration is approximately 0.12". However, this value varies with condition and geometry of the wedge surfaces. The technical contact must be consulted before this special test is requested. back to top | back to index of dimensional measurements ## Special Angular Measurements, by Prearrangement (14050S)For angular measurement requirements not covered by the services described above, special arrangements may be made by contacting Engineering Metrology Staff 301-975-3471. Requests for service will be discussed and honored if current equipment and means are available. Artifacts such as optical squares (pentaprisms), apex angle measurements of prisms, true squares, and polygons not already described, typically fall into this category. back to top | back to index of dimensional measurements ## References-Angular MeasurementsUncertainty and Dimensional Calibrations, Ted Doiron, John R. Stoup, J. Res. Natl. Inst. Stand. Technol. The Calibration of Angle Blocks by Intercomparison, C. P. Reeve, Natl. Bur. Stand. (U.S.), NBSIR 80-1967 (1980). The Calibration of Indexing Tables by Subdivision, C. P. Reeve, Natl. Bur. Stand. (U.S.), NBSIR 75-750 (1975). back to top | back to index of dimensional measurements Program questions: Calibrations Phone: 301-975-2200, Fax: 301-975-2950 NIST, |