Page 88 - Engineering drawing from first principles using AutoCAD

Pictorial projections 81

course use the MOVE command but I prefer not to do this since it is often easier to have
two bites at the cherry if problems arise, since I still have the original.
Plot the profile of the 'V' on the top surface and transfer a copy to the bottom. Clean up
the drawing with BREAI< and TRIM.

Repeat the procedure by copying the top view in its new position and then add the short
tangent to the two semicircles. Use the ZOOM feature to get the maximum size of image
on the screen for clarity and engage SNAP for guaranteed accuracy whenever possible.
Further examples of isometric and oblique projections are shown in Figs 3.11-3.13.
In Fig. 3.14 a method of setting out the hexagon is shown by taking the distance
across the flats and the distance across the corners from the orthographic view and
marking out equal dimensions along the main isometric axes by the use of circles. To
avoid confusing construction lines on the main drawing of many features, it is often
easier to construct detail away from the main drawing and simply insert it using COpy
or MOVE commands.
In the bracket shown in Fig. 3.15 there are two similar holes with centre lines, and the
technique here is to draw one in a clear space away from the drawing and then use two
copies in the correct position. In Fig. 3.16 the sloping face at 45° has the effect of
producing a single line on the left side of the oblique view. An alternative solution can
be presented with the receding side at 30° as shown in Fig. 3.16(b)-(d).

Drawing notes for Fig. 3.17
This exercise shows a small moulding to be drawn in isometric and oblique projection.
Draw the given dimensioned example.
In each solution there are three vertical planes. For the oblique solution take a copy of
the left-hand given view, to be used as a datum. Erase all dimensions. Position another
copy 5mm to the rear at 45° and use the BREAI< command to remove the hidden
parts. Add the top left and bottom right corner lines. Project forward the two semi-
circles and reposition them at 18mm towards the foreground. Then add the tapered
side lines.
The isometric view needs to be set out using the isometric grid. You may find that it is
easier to draw the ellipses away from the solution since only halves and quarters are
needed. Use COpy and MOVE features to separate the required parts. The advantage of
this method is to reduce the number of construction lines in such a small area. If
construction lines have previously been drawn to establish the outline, then finished
polylines can be repositioned with accuracy. Remember to use the SNAPfeature with the
appropriate settings and the ZOOM command.