Page 22 - Engineering drawing from first principles using AutoCAD

First steps 15

Select Array in the Construct menu and the command line reads

Command: _array
Select obj ects :
Click on the drawing at the bottom left-hand corner and then again at the top right-hand
corner so that the drawing is enclosed by a box. The command line reads Select
obj ects: Other corner: 16 found. The drawing is highlighted so click and press
<Enter>. The command line now reads Rectangular or Polar array (RIP) <R>:.
Type P and press <Enter>. The command line answers Cen tre poin t of array: . Click
on the intersection of the centre lines that positioned the axis through wheel J. Press
<Enter> and the command line responds Number of items:. Let us assume that we
would like five parts to our illustration, so type 5 then press <Enter> and the command
line replies Angle to fill (+=ccw, -=cw) <360>:. We require our five parts equally
0
spaced around 360 so simply press <Enter> again and the drawing shown in Figure 1.15
will appear.

Fillet applications

The FILLET feature is useful for joining lines and arcs automatically with an arc of a
specified radius. Fig. 1.16 shows three pairs of lines which I have drawn at random angles
and with random radii.
I want to join the lines with a fillet radii of, for example, 14 mm and have spaced the pairs
of lines so that such a size of radii will fit. If it does not do so because the lines are not far
enough apart to accommodate it, the computer will reject the fillet request and this
message will appear:
Radius is too large
, Invalid'
Command:
To set the fillet radii choose Fillet from the Construct menu and the command line will
read:
Command: _fillet Polyline/Radius/<Select first object>:
Type R and the line will change to En ter fillet radius <2 . 0000>: 14. Press <Enter>
and the line returns to Command: .
Note that the value of 2.0000 above was the previous value used. The value of 14 mm is
the current set value for the fillet radii and will remain until we modify it. Choose Fillet
again from the Construct menu and the line returns to
Command: _fillet Polyline/Radius/<Select first object>:

Click on one line and the command line changes to Select second obj ect:. Click on
the second line of the pair and the fillet is drawn. Repeat the procedure for the other pairs
of lines.
The situation now is that we have a continuous thin line but would like to define the
tangency points and the fillet arc centre. Finally we need to thicken up the profile for a
finished outline. From the Modify menu choose Edit Polyline as previously described
and adjust the line width to 0.4 mm. Repeat this again for the other pairs.

Turn off the Ortho and Snap features since the line we are about to draw will come from
an exact point which will not coincide with points on our grid. In order to find the centre
points for the fillet radii we can again use the Draw menu, select Line, then click on
Assist and in the Running Object Snap box make sure there are no other entries and
select Centre. The command line reads