Elements of descriptive geometry, with applications to isometric projection and othe forms of one-plane projection; a text-book for colleges and ingineering schools by O. E. Randall.

ISOMETRIC PROJECTION

203

determine the coordinates of any point on the lid with reference to
a horizontal and to a vertical plane through the hinge axis D-E.
The point F, for example, one apex of the lid, is at the distance
F-g above the horizontal plane and at the distance F-k back of
the vertical plane. The point F is also in the plane of the left-hand
end of the box, and in isometric projection will be located with
reference to the isometric axes o'-z' and o'-y.
In Fig. 179 make d'-g' equal to D-g of Fig. 180, and through
g' draw g'-fl parallel to the axis o'-y'. Lay off upon g'-f' from g'
the distance g-F of Fig.
180. The point f' is the
isometric projection of F.
In this way the isometric projection of any point
on the lid may be deter-
mined.
The isometric projec-
tion of S, one of the inner 3/
vertices of the lid, is found
thus: In the end view,
Fig. 180, the point S will
appear at P, at the distance P-q below the horizontal plane and at the Yf
distance P-r back of the
B, IG. 181
vertical plane.
In Fig. 179 make d'-q' and q'-p' equal respectively to D-q and
q-P of Fig. 180, locating p'. Through p', which is the isometric
projection of P, draw p'-s' parallel to o'-x', to represent the inner
horizontal edge of the lid.
Through t' previously located draw t'-s' parallel to f —'T, to
represent the inner vertical edge of the lid.
The point s', the intersection of p'-s' and t'-s', is the isometric
projection of S.
443. Problem 308. To represent a mortise and tenon. See Fig. 181.
444. The Isometric Projection of Curved Lines. The isometric
projection of curved lines may be determined by finding the