## Mechanical Drawing

In this department we purpose explaining, by the help of appropriate diagrams, die easiest method» of delineating various portions of machinery. In this, as in the others just treated of, the application of the constructions which we have given in Practical Giometry will be very obvious on inspection. The preliminary lessons also of the department of this work on Architectural Drawing will be of use in enabling the pupil readily to master the constructions we now place before him.

Example 1, fig. 1, represents a ' bolt* cb, with the solid head ¿d, and movable ' nut1 g'g. This is used for strongly fastening various portions of machinery together. For examples of the method of using this, see our work on Mechanics and Mechanism in this Series. To draw the figure now given. Suppose the copy to be without the centre-line; bisect efef in the point Of draw ab\ On the paper on the drawing-board draw two lines eV, ab' at right angles to each other; with ai from the copy measure from the point of intersection of the above lines on the board a to eV; from a measure to b; from b with distance ae measure to d, d; join det, dd. From a measure to c and V; from these points with ai measure to </gy <fg; join gig', gg. From b measure to h} h; parallel to ab' from h> h draw lines g.l.

Example 2, fig. 2. Bisect the line b'b' of the copy in the point d% and draw db. On the paper on the board draw two lines corresponding to these, intersecting at the point d.* From d measure to b\ bfrom d measure to c; with ab' from this point measure to ff; draw a line parallel to W through e; join fb', From a or c measure to d, and through this draw a line parallel to b'b'. From c measure to g,g; join (f g by perpen

* To avoid repetition the pupil is requested to observe that, in all the lessons, the centre-lines drawn on the various diagrams must be drawn on the paper on the board, it being understood that where a copy is presented him in this book, or elsewhere, without centre-lines being given on it, that these should be adopted and drawn in faint lines, so that data may be given from which to take measurements. By dint of practice the facility for copying without these will be attained, or, at least, they will be sparingly required. As tne pupil proceeds he will the more readily decide as to the quickest method of finding datum points from which to take measurements.

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