First angle projection examples with plotted curves

In orthographic projection, all widths in the end view are equal in size to depths in the plan view, and of course the opposite is true that some dimensions required to complete end views may be obtained from given plan views. Figure 4.21 shows part of a solid circular bar which has been cut at an angle of 30° with the horizontal axis. Point A is at any position along the sloping face. If a horizontal line is drawn through A across to the end view then the width of the chord is dimension X. This dimension is the distance across

Engineering Drawing With Dimension
(c) Fig. 4.18
Orthographic Drawings 1st Angle
Face DimensionsFirst Angle Projection
Fig. 4.21

the cut face in the plan view and this has been marked on the vertical line from A to the plan. If this procedure is repeated for other points along the sloping face in the front view then the resulting ellipse in the plan view will be obtained. All of the examples in this group may be solved by this simple method.

A word of warning: do not draw dozens of lines from points along the sloping face across to the end view and also down to the plan view before marking any dimensions on your solution. Firstly, you may be drawing more lines than you need, and in an examination this is a waste of time. Secondly, confusion may arise if you accidently plot a depth on the wrong line. The golden rule is to draw one line, plot the required depth and then ask yourself 'Where do I now need other points to obtain an accurate curve?' Obviously, one needs to know in the plan view the position at the top and bottom of the slope, and the width at the horizontal centre line and at several points in between.

In the examples shown in Fig. 4.22 three views are given but one of them is incomplete and a plotted curve is required. Redraw each component using the scale provided. Commence each solution by establishing

Third Angle ProjectionThird Angle ProjectionWww First Angle Projection First Angle Projection Orthographic Slanted


Third Angle ProjectionWww First Angle Projection

the extreme limits of the curve and then add intermediate points.

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