Page 35 - Engineering drawing from first principles using AutoCAD

Chapter 2
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Geometrical

applications

This chapter introduces you to:
• Dimensioned tangency examples.
• Tangency points and intersecting arcs.
• Polar and Rectangular arrays.
• Ellipse construction and properties.
• Scale factors.
• Wire parts.
• Symmetrical layouts.
• Double lines and arcs.
• Wire springs.
• Setting out exact rotation angles using the Gear Wheel example.
• Gear Wheel terminology.
• UNDO, REDO, BREAI(, EXTEND and TRIM features.
• Loci.
• Archimedian Spiral.
• Cylindrical and conical helix.

Tangency

In order to gain experience and proficiency, it would be desirable after completing each of
the following drawing exercises to add the dimensions which are provided. Please accept
this as a desirable form of 'on the job' training. Continuous practice is necessary to
improve speed, familiarity and overall efficiency.
The dimensions follow the procedures and practices recommended in British Standards.
It is essential to show accurate and unambiguous dimensional details.

Dimensioning is a very important part of engineering drawing and Chapter 5 details
other aspects not illustrated in these examples. Please therefore refer to this information
while you make progress in copying the applications throughout the book. The following
examples emphasise where lines and curves join, so that the exact length and position of
each small part can be understood.

Light bulb

Tangency points for the position of joins between intersecting arcs may be found by
constructing lines between the arc centres (Fig. 2.1). Set out the given basic features and
determine the positions of tangency points X and Y using the construction lines indicated
from centres P, Q and R. Line in the profile with a polyline of O.4mm width and add the
dimensions to complete the detail.
The lamp profile can also be drawn by positioning part of the RSO and R80 radii as shown