Unit13_Angular_Measurement.ppt
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The document discusses tools and methods for measuring angles in machine shops, including universal bevel protractors, sine bars, and sine plates. A universal bevel protractor can measure angles to within 5 minutes of a degree using a vernier scale. Sine bars are used to measure angles more precisely, within 1 minute of a degree, by creating a right triangle with gage blocks. Sine plates are wider versions of sine bars that allow clamping workpieces to measure or machine angles more accurately.
Unit13_Angular_Measurement.ppt
- 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar • Gill • Smid Technology of Machine Tools 6th Edition Angular Measurement Unit 13
- 2. 13-2 Objectives • Make angular measurements to an accuracy of 5' (minutes) of a degree using a universal bevel protractor • Make angular measurements to less than 5' of a degree using a sine bar, gage blocks, and a dial indicator
- 3. 13-3 Angular Measurement • Important phase of machine shop work • Most common tools – Universal bevel protractor – Sine bar – Sine plate
- 4. 13-4 • Precision angles to within 5' (0.083º) • Consist of base – Vernier scale – Protractor dial – Sliding blade – Dial clamp nut Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Universal Bevel Protractor
- 5. 13-5 Vernier Protractor • Used to measure obtuse angle (90º-180º) • Acute-angle attachment fastened to protractor to measure angles less than 90º • Main scale divided into two arcs of 180º – Scale divided into 12 spaces on each side of 0 – If zero on vernier scale coincides with line on main: reading in degrees Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
- 6. 13-6 Reading a Vernier Protractor Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Note number of whole degrees between zero on main scale and zero on vernier scale • Proceeding in same direction, note which vernier line coincides with mail scale line 50º Fourth – Multiply number by 5' and add to degrees on protractor dial 4 x 5'= 20' Reading = 50º 20'
- 7. 13-7 Sine Bars • Used when accuracy of angle must be checked to less than • Consists of steel bar with two cylinders of equal diameter fastened near ends – Centers of cylinders exactly 90º to edge of bar – Distance between centers usually 5 or 10 in. • Made of stabilized tool hardened steel
- 8. 13-8 Sine Bars • Used on surface plates and any angle by raising one end of bar with gage blocks • Made 5 in. or in multiples of 5 in. • Lapped cylinders with 5 in. ±.0002 or 10 in. ± .00025 between centers • Face accurate to within .00005 in. in 5 inches
- 9. 13-9 Sine Bars • Hypotenuse of a right-angle triangle – Gage block buildup forms side opposite – Face of surface plate forms side adjacent angle required of sine X 5 buildup 5 buildup bar sine of length buildup block gage hypotenuse opposite side angle the of Sine
- 10. 13-10 Example Calculate the gage block buildup required to set a 5 in. sine bar to an angle of 30º angle required of sine X 5 buildup buildup = 5 (sin 30º) = 5(.5000) = 2.5000 in. Note: This formula applied only to angles up to 60º .
- 11. 13-11 Sine Bars • Angles > 60º – Better to set up work using complement of angle – Angle plate turned 90º to produce correct angle • When sine bar in near-horizontal position, small change in height of buildup will produce smaller change in angle than near-vertical position • Small angles – Sometimes impossible to get buildup small enough to place under one end of sine bar • Place gage blocks under both rolls of sine bar • Net difference in measurement equal to required buildup
- 12. 13-12 Sine Bar Used to Check Taper Necessary to check angle of taper so proper gage block buildup can be made In right triangle, ABD: D B A C 12.000 1.000 .500 0 2 6 4 4 a 0 1 6 4 2 04166 . 12 2 1 2 a Tan a
- 13. 13-13 Sine Bar Used to Check Taper (cont.) From the solution prior, the following formula for solving the included angle, when the taper per foot (tpf) is known is derived. By transposition, if the included angle is given, the tpf may be calculated as follows: 24 X 2 1 tan a tpf
- 14. 13-14 B A C 3.187 1.000 1.750 a a/2 Sine Bar Used to Check Taper (cont.) If the tpf is not known, the angle may be calculated as follows: in. 1.1598 .23196) 4 4 4 2 13 sin 5 Buildup 4 4 4 2 13 a 2 2 2 4 6 11766 . 187 . 3 375 . 2 a tan 375 . 2 000 . 1 750 . 1 AC
- 15. 13-15 Tapers • Metric tapers expressed as ratio of 1 mm per unit of length – Ratio of 1:20 means would taper 1 mm in diameter in 20 mm of length • Can be checked conveniently and accurately with taper micrometer – Measures work to sine bar accuracy while work still in machine
- 16. 13-16 Sine Plate • Based on same principle as sine bar – Similar in construction except it is wider • Sine bars up to 1 in. wide • Sine plates generally more than 2 in. wide • Several tapped hole in surface – Permit work to be clamped to surface of sine plate • End stop prevents workpiece from moving during machining
- 17. 13-17 Sine Table • Sine plate hinged to a base • Both sine plate and table – Supplied in 5 and 10 in. lengths – Have step or groove of .100 or .200 deep ground in base to permit buildup for small angles to be placed under free roll
- 18. 13-18 Compound Sine Plate or Table • Consists of one sine plate superimposed on another sine plate – Lower plate hinged to base and may be titled to any angle from 0º to 60º by placing gage blocks under free roll or cylinder – Upper base hinged to lower base so that cylinder and hinge are at right angles to lower plate • Can be tilted to any angle up to 60º • Permits setting of compound angles • Not used until finishing operation (grinding)