Practical engineering drawing and third angle projection, for students in scientific, technical and manual training schools and for ..draughtsmen .. . volute and the Spiral of Archimedes. Of less practical importance, though ecjually interestinggeometrically, are the other curves mentioned in the heading. The student should become thoroughlj^ acquainted with the more important geometrical proper-ties of these curves, both to facilitate their construction under the varying conditions that may ariseand also as a matter of education. Considerable sjDace is therefore allotted to them here. At this
Practical engineering drawing and third angle projection, for students in scientific, technical and manual training schools and for ..draughtsmen .. . volute and the Spiral of Archimedes. Of less practical importance, though ecjually interestinggeometrically, are the other curves mentioned in the heading. The student should become thoroughlj^ acquainted with the more important geometrical proper-ties of these curves, both to facilitate their construction under the varying conditions that may ariseand also as a matter of education. Considerable sjDace is therefore allotted to them here. At this point Art. 58 should be reviewed, and in addition to its suggestions the student is fur-ther advised to work, at first, on as large a scale as possible, not undertaking small curves of sharpcurvature until after acquiring some facility in the use of the curved ruler. THE HELIX. 120. The ordinarj helix is a curve which cuts all the elements of a cyhnder at the same we maj define it as the curve which would be generated by a point having a uniform motionaround a straight hue combined with a uniform motion parallel to the line. Xig-. ffluuuuuuuuumuumuui The student can readily make a model of the cylinder and helix bydrawing on thick paper or Bristol-board a rectangle A B 0 D (Fig. 81)and its diagonal, D B; also equidistant elements, as m 6, n c etc. Allowat the right and bottom about a quarter of an inch extra for overlapping, as shown by the lines x y and .s z. Cut out the rectangle z x ; also cut a series of verticalslits between D C and zs and turn the divisions up at right angles to the paper; put mucilagebetween B C and x ij; then roll the paper up into cylindrical form, bringing A D t ft in front 40 THEORETICAL AND PRACTICAL GRAPHICS. of and upon the gummed i^ortion, so that A D will comcide with B C. The diagonal D B willthen be a helix on the outside of the cylinder, but half of which can be seen in front view, as D7, (see right-hand figure) ; the other hal
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Keywords: ., bookcentury1800, bookdecade1890, booksubjec, booksubjectlettering
