Page 74 - Engineering drawing from first principles using AutoCAD

Geometrical applications 67

The elevation shows two curves. A left-hand helix starts at point 1 and its projection is
shown completely in the plan view. Note that at divisions 4 and 10 it is necessary to
draw radii to establish the two points on the centreline. The other right-hand helix
starts at point 10 and is constructed using the same method but with the direction of
rotation reversed. Applications are found in fairground amusements and mechanical
handling equipment.

Wire springs
A method of drawing wire springs is given in Fig. 2.36, where the points on the helix are
projected as before and at each point a circle is drawn to represent the wire diameter.
Tangents between adjacent pairs of circles need to be drawn to form continuous lines as
shown in stage 1, which are then converted to polylines. Use the MIRROR and COpy
features to add together the separate sections as mentioned previously.

Draw stage 1 for a spring with a mean diameter of 70mm and a coil lead of 30mm.