Inspecting a Simple Angle The photo above shows a workpiece on which an angle of 30º is required. The workpiece is resting on a parallel* which is wrung to angle blocks forming 30º. The entire set-up is lined up vertically with an angle plate and then indicated across the top of the work to determine the correctness of the angle. * Parallels are not necessary, but they are convenient because of their longer reference surface. Ease and Versa tility A set consisting of only 16 blocks will measure 356,400 angles in steps of one second, to an accuracy of 1/5,000,000th of a circle! These micro-accurate blocks can be used in either plus or minus positions. In example "A", take the 30º angle and add the 5º angle to obtain a measurement of 35º (making sure that both plus ends are together). In "B", use the same two blocks but wring them together so that the minus end of the 5º block is over the plus end of the 30º block. This will subtract 5º from 30º, thus giving a 25º measurement. Indexing a Large Rot ary Table A Webber Angle Block or True Square is positioned on the work and a beam of light from an autocollimator is directed against the gaging surface. This becomes 0º, or the reference surface. Other angle blocks are then added in proper combination to measure each succeeding angle. The table is rotated and inspected at each position with reference to the light beam. This method indexes large workplaces quickly, with accuracy measured in fractional seconds. Setting a Revolving Magnetic Chuck A chuck is set for a 38º angle. Three blocks, +30º, +5º and +3º, are assembled and mounted with the parallel*. The indicator quickly tells if the setting is accurate. Adjustment is a matter of seconds. A revolving chuck teams up perfectly with angle blocks to make possible several applications in tool grinding that are more difficult with other methods. Using Angle Gage Blocks SUPERIOR TO SINE BAR METHODS A precision angle has always been difficult to set because of the involved trigonometric formula that is used with the sine bar. The main difficulty lies in the dimension X in diagram, which oftenresultsinafigurewithmanydecimalplaces.Gageblocks can only approximate this value. For example, to measure 44º 30' using a 5" sine bar the following steps are required: With angle gage blocks, you take a 45º block from the set, wring on a 30' block so that the plus end of 45º block contacts the minus end of 30' block,and you have an angle of 44º 30'. It is not only easy to accomplish, it is absolutely accurate. Sine for 44º 30' angle .7009093 For dimension X multiply by 5 3.5045465 Gage Blocks necessary to match this dimension .1005 .104 .300 3.000 3.5045 3.5045465 – 3.5045 = Residual error .0000465 This error cannot be eliminated in sine bar procedure. Webber Gage Blocks X Angle Gage Block Specifications Accuracy In Microinches (Microns) Material Reference Grade croblox® Calibration Grade Steel Tolerances: Deviation From Nominal ±1.0 second ±2.0 second Flatness of Gaging Surfaces 6µin. (0.15µm) 8µin. (0.20µm) Flatness and Parallelism of Sides 8µin. (0.20µm) 8µin. (0.20µm) Squareness of Sides to Gaging Surfaces 6 seconds 8 seconds Area of Gaging Surfaces† 1 x 2" (25 x 50mm) 1 x 2" (25 x 50mm) Surface Finish (Gage Surfaces Only) 0.4µin. AA (.01µm AA) 0.6µin. AA (.015µm AA) Estimated Uncertainty of Measurement (k=2) 0.6 seconds 1.0 seconds Flatness tolerances exclude 1.5mm from the edges on all angle blocks, except where marked with **. Then 3mm from the edge is excluded. † Dimension of gaging surfaces in millimeters is approximate. A B 35° 25° 30 Deg. 30 Deg. + – + – – + + – 400 S t arrett -W ebber G age B locks