Page 58 - Engineering drawing from first principles using AutoCAD

Geometrical applications 51

Set out construction lines to fix the centre, the position of the angle and the ends of the
spring as shown in stage 1. Draw circles of R28 and R32 and break them at the bottom
right-hand corner since we are going to use the FILLET command at each side. In the
Draw menu select the Double Line option. The command line reads
Command: _dl ine
Break/Caps/Dragline/Offset/Snap/Undo/Width/<startpoint>:
We need first to specify a width so type Wand press <Enter>. Note that the line reads
Break/Caps/Dragline/Offset/Snap/Undo/Width/<startpoint>: W
New DLINE width<8>:
The previous line width was 8, so now type 4 and press <Enter>. Note change to

Break/Caps/Dragline/Offset/Snap/Undo/Width/<startpoint>:
Click on the point at the bottom of the spring in the 6 o'clock position and the next
command reads

Arc/Break/CAps/CLose/Dragline/Snap/Undo/Width/<nextpoint>:
Click with the left button about 35mm above as shown. Click again with the right-hand
button to enter and the command line returns to Command: .
We can re-enter the previous command again by clicking with the right mouse button
and repeating the process. If the SNAPbutton was engaged you will need to turn it off to
ensure that the angle of 30° is exactly positioned on the vertical line through the end
position on the component. If this has been done, then the last click during the process
will close off the end of the parallel lines.
Use the FILLET command to insert the two pairs of radii. This needs to be done using radii
of 18 and 22 since the mean radius of the centre line is 20mm. Use the EDITPOLYLINE
command to give a finished drawing.

Double arc construction

Double lines can be arcs or straight lines and Fig. 2.24 shows a scale drawing of a layout
for a model train set to illustrate some of the features available.

Draw a 100mm diameter circle through points A, B, C and D. Select Double Line in the
Draw menu and the following options will appear at the command line:

Break/Caps/Dragline/Offset/Snap/Undo/Width/<startpoint>:
Click on point A and the command line reads
Arc/Break/CAps/CLose/Dragline/Snap/Undo/Width/<nextpoint>:

Type A and press <Enter>, then Wand <Enter> and command line reads New DLine
Width:. Type 4.
Double lines can be capped or left open so type CA and the command line gives the
options Both/End/None/Start/<auto>:. Select None and type N. Click on point B,
followed by C for the end point and a double semicircle is drawn. Type CL and the circles
are completed.
Copy the three circles 110mm to the right to give E, F, G and H. Construct the three
tangent lines separately using the OBJECT SNAP feature. Insert the double lines above
for the train sidings. The three junctions can be completed using the FILLET feature with
radii of 52, 54 and 56mm.