Page 177 - Engineering drawing from first principles using AutoCAD

170 Engineering drawing [rom first principles

distances between points 1,2, 3, 4 and 5 are not equal, but if the curve is only required to
complete an assembly drawing then this construction will be satisfactory.
Now draw a pattern development for the cone by saving this drawing under a new file
number and deleting all construction lines. Figure 7.17 shows the new constructions
where the angles between 01, 02, 03 and 04 are equal and 15°. Project radii from the
plan to the sloping side in the front view and establish the true lengths from the top of the
cone to the intersections equal to R1, R2, R3 and R4. Figure 7.18 shows the constructions
for the cone pattern. Draw part of a circle of radius RI00, the slant height of the cone. The
angle of the pattern is
120 X 1t
X 360 = 216°
200 X 1t
Draw the line a1 and plot the pattern blank by the method shown earlier for Fig. 7.12
using the ARRAY feature. It is only necessary to draw a quarter of the pattern curve using
the true lengths as shown between points 1 to 7. Repeat the profile a further three times
to complete the construction. The MIRRORfeature can be used but ensure that you start
the construction with vertex a on a GRID point for accuracy in defining the mirror lines.
Alternatively, you can use the ARRAY feature.