Notes on technical sketching and free hand lettering for engineering students by Smith Alton Lincoln 1867-

Author:Smith, Alton Lincoln, 1867- [from old catalog]
Language: eng
Format: epub, pdf
Tags: Mechanical drawing, Lettering
Publisher: Worcester, Mass., The author
Published: 1912-03-25T05:00:00+00:00

197. The major axis should always be dra'wii or imagined '\\heu drawing an eUipse and the cm"ve should be made symmetrical on it. Havmg both axes given, mark the center of the elhpse and then spot points for the four ends of axes. Draw the curve through these four points.

198. Referring to Fig. 46, B, let the plane of the cncle parth' shown by the arc HLK be parallel to the plane of projection. Let equal di\isions be marked on it as mdicated. Xow revolve the circle on a hne, CH, coincident with its diameter, until it projects as the ellipse of which one-half is SHJ. Any division point as L on the circle will, during the revolution, remain in a plane perpendicular to the axis and the projection of L will be foiind somewhere on a Une L^l perpendicular to CH. As the projection of L must also be on the ellipse, it will be found at AI.

It is seen, that equal divisions on the cu'cle are not so on the elhpse, its projection, but that they shorten gradually toward the end of the major axis. This construction will give results of considerable accuracy, even though drawn free-hand. ^\Tien some knowledge of the rate of shortening is acquired, the consti-uction may be dispensed ^^-ith. The gear teeth m the drawing were spaced by the eye and not quite accurateh^, as the construction shows. It is true, however, that the error is scarceh^ noticeable.

199. Having a circle and one of its diameters, if a chord be drawn parallel to the diameter and bisected, a diameter through the point of bisection will be perpendicular to the

first diameter. Now place the cii-cle so its plane is obhque to the plane of projection and the projection of the circle becomes an eUipse. The diameter and parallel chord project as parallels and the chord is stiU bisected. The projection is shown in Fig. 30.

Having an elhpse ABCD representing a circle, and a line, 1-2 representing a diameter of that ckcle, to find the line representing a diameter perpendicular to 1-2, construct as follows. Draw a chord 3-4 of the eUipse parallel to 1-2, bisect it at 5 and draw the required line 6-7 through point 5 and 0, the center of the ellipse.

200. The draftsman should acquu-e familiaritj' with the shapes of various elhpses. Several should be constructed accurately bj' the method sho^^^a in Fig. 30. Draw two lines AB and CD at right angles

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