. A textbook on mechanical and electrical engineering . 360 parts. Each division is one-half of one degree, and, forconvenience, the degrees are numbered from 0° to 180 from M. E. 18 GEOMETRICAL DRAWING §1 both A and B. The protractor is used for la)ing off ormeasuring angles. Protractors are often made of metal,in which case the central part is cut away to make thedrawing under it visible. When using the protractor, itmust be placed so that the line OB. Fig. 19, will coin-cide with the line forming one side of the angle to be laidoff or measured, and the center O must be at the vertex of
. A textbook on mechanical and electrical engineering . 360 parts. Each division is one-half of one degree, and, forconvenience, the degrees are numbered from 0° to 180 from M. E. 18 GEOMETRICAL DRAWING §1 both A and B. The protractor is used for la)ing off ormeasuring angles. Protractors are often made of metal,in which case the central part is cut away to make thedrawing under it visible. When using the protractor, itmust be placed so that the line OB. Fig. 19, will coin-cide with the line forming one side of the angle to be laidoff or measured, and the center O must be at the vertex ofthe Fig. ej For example, let it be required to draw a line throughthe point C, making an angle of 54° with the line £ F,Fig. 20. Place the protractor upon the line £F, as justdescribed, with the center O upon the point C. With asharp-pointed pencil, make a mark on the paper at the54 division, as indicated at D. A line drawn through Cand D will then make an angle of 54° with £ F. Greaterexactness will be secured if the line £F be extended tothe left, so that both zero marks (A and B, Fig. 19) canbe placed on the line. This should always be done whenpossible. liETTERIXG 20. In mechanical drawing, all headings, explanatorymatter, and dimensions should be neatly printed on thedrawing. Ordinary script writing is not permissible. § 13 GEOMETRICAL DRAWING 19 It is usually difficult for beginners to letter well, andunless the student is skilful at it. he should devote sometime to practicing lettering before commencing the correcting the plates, the lettering will be considered a
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