Page 167 - Engineering drawing from first principles using AutoCAD

160 Engineering drawing [rom first principles

Transfer lines from the intersections on the sloping face to the pattern as shown. Draw a
polyline through these plotted points. Select Fit from the Edit Polyline feature to obtain
the curve.
It is an interesting AutoCAD exercise to draw the illustration in Fig. 7.8 using details from
Fig. 7.7. Save your drawing with a new file name and erase the dimensioned part on the
left. Rotate the elevation through 180° about centre P. The pattern profile is already in
position but it is necessary to make modifications to its size and the numbering. Confirm
the results by taking a print from each drawing and cutting out the patterns to make a
model.

Cylindrical branch

The dimensions of a cylindrical branch are shown on Fig. 7.9. Provided the main duct and
the branch are the same diameter, then the intersection between the two on the elevation
will be formed from straight lines.
The main duct requires a hole to be cut to insert the branch. The procedure for the pattern
length and its division is the same as that previously described. To improve accuracy, an
intermediate point can be added between points 1and 2. Use the ZOOMfeature and draw
a small line at 15°. Project a vertical line to the intersection, and as much of the horizontal
line from the intersection to the left that the screen area will allow. Use the EXTEND
option to extend this line to the pattern. To fix the position on the pattern, bisect the
distance between points 1 and 2 by drawing small intersecting circles of the same radii
and drawing a line through their intersections.
The pattern development for the branch pipe is inconvenient to draw if projected at an
angle from the given view. A better method is to make a copy of the branch and rotate it
through 45° anticlockwise to bring the required part into the vertical position. The
complete pattern is shown so take a print of your solution and make a model.

Development of hexagonal pyramid

The dimensions of a hexagonal pyramid are given in Fig. 7.10 and the pattern construc-
tion for the surface on Fig. 7.11.

Number the corners and commence the pattern by drawing a radius equal in length to the
slant height 04 (Fig. 7.11). Draw line 02 at a convenient position. Draw an arc of radius
R2 on the plan from point 2 on the pattern circumference to give point 1. The complete
pyramid consists of six triangles similar to 012. Use the ARRAY feature to draw and
number them as shown.
The pyramid is cut vertically in the plan view and the surface 7,8,9,10 needs to be
positioned on the pattern. Extend the line from 8 to 9 in the front view to the side of
the pyramid at point P and draw radius OP to intersect lines 05 and 06 on the pattern.
This construction is necessary to determine the true length of distances 08 and 09. Draw
an arc of radius R from points 4 to lOin the plan from centres 1 and 4 on the pattern in
order to fix points 7 and 10 on the pattern. Join the points as shown to complete the
pattern development.

Conical development

Part of a cone made from thin sheet metal is shown in Fig. 7.12. A pattern is required for
the curved surface; it is cut from part of a circle whose radius is equal in length to 01, the