I have chosen a fairly complex drawing for this tutorial, with unusual curves and orientations. The best way to approach such a task is to draw some construction lines and then edit those to form the three cross-hatched shapes in the drawing, as well as to lay out the other linework at the end of the process. It is unlikely that you will understand how the construction lines will be used until the end of the process, so you will just have to trust me! Fortunately, it turns out that most of the basic CAD operations will be encountered as we work through these steps.

STEP 1

The first step is illustrated in Figure 2 (over the page) and consists of drawing a square, diagonal and arc. We will draw the square first.

As with all CAD tasks, we have to begin with an entity of a fixed size ... in this case, a square that is either 45000 or 150 units in size, depending on how you are viewing the drawing! Almost everything else is constructed from that square. We are going to type in the coordinates that define the square, because that is the most accurate way of entering graphic information. We will use the Line command, using the mouse to nominate an arbitrary starting point (towards the lower left corner of the drawing area on the screen) and then typing in the coordinates of each of the corners of the square relative to the previous corner, either as a coordinate pair (delta-x & delta-y) or a distance and an angular direction (called a polar coordinate).

You might be tempted to wonder why we don’t use the Rectangle command to draw this square … that would produce a single entity (the rectangle) while we actually want four separate lines … later you will discover that we could use Rectangle and then "explode" it, but that is a different story …

Having set up all the construction lines, the next task is to selectively edit the construction lines in order to form the three cross-hatched forms that constitute the focus of this drawing. This will be done in three steps.

The first step is to isolate the particular construction lines that will be trimmed and modified to form the three shapes. This is done by moving all the extraneous lines to a separate "layer" in the drawing and then making that layer invisible. The remaining lines will then be edited in Step 2 to form the three shapes shown in Figure 1. Figure 7 shows all the extraneous lines as dashed. Your task (refer to the instructions given below) is to create a new layer, select each of the lines shown dashed in Figure 7, and then move them to that new layer. You will then make that layer invisible before proceeding to next step.

Click the Layer button (in the dialogue box) and then select the "construction" layer that you just created. Click OK and OK again!

All the lines that are shown dashed in Figure 7 should now have disappeared ... your drawing should look like the first drawing in Figure 8(a) … if you missed any, then just repeat the process just described!

STEP 2

For this step, you have to use the Trim command to clean up all the excess lines in order to convert the construction lines that are left on the screen into the three shapes shown in Figure 1. This is best done in 5 phases as illustrated in Figures 8 (a) - (e). In each Figure, the left illustration shows which lines to select as "cutting edges" (marked with small squares) and which ones to select as "elements to be trimmed" (marked with small circles) ... the right illustration then shows what the drawing will look like after that trim operation.

At the moment, each of these primary shapes is made up of a sequence of four or five connected, but distinct, line or arc segments. The final step involves taking these three primary shapes and forming each into a single geometric element. In AutoCAD, these are referred to as closed polylines. Once they are each single entities, then it is easy to thicken the lines and cross-hatch them to complete the forms. After that, the last task then will be to draw in the rest of the objects using the construction lines as guides.

To convert each of these objects into a single entity, you use a command called Pedit (an abbreviation of "polyline edit"). The same command is used to set the line width once these polylines have been created. Thus, for each of the three shapes in turn, proceed as follows ...

To cross-hatch the closed polylines, we use the Boundary Hatch command. Once you have issued that command, you will get the following dialogue box.

This dialogue supports a number of hatching options. You can use either pre-defined or user-defined hatch patterns. In this case it would be easier to use a user-defined pattern, so select that option in the Pattern Type section of the dialogue. Set the Angle to 45 as shown, and the Spacing to 1200 {or 4 where appropriate!}. You can then use either the Pick Points or the Select Objects buttons: in the first case, you then simply pick a point anywhere inside each of the three shapes (and AutoCAD will search for and identify the enclosing shape); in the latter case, pick each of the three polyline shapes directly. In either case, once the boundaries have been defined, press ¿ to bring back the dialogue box and then click APPLY.

The final stage of this drawing is left up to you to complete, using Figure 9 as a guide! You should begin by turning on the construction line layer (see instruction in left margin), and then, using Figure 9 as a guide, construct the rest of the linework for this plan (on layer 0), guessing at the dimensions where lines don’t actually follow the construction lines.

Be assured that you can construct all those lines using the commands that have been introduced in this tutorial including Offset, Trim, Fillet and, of course, the Snap Modes. Where appropriate, use the construction lines themselves by trimming them down, but don’t forget to use the Change Properties command to move them to layer 0.

Up to this point, the drawing that you have produced has been created in what AutoCAD calls model space (where design objects are described in their real-world size). You are now going to switch to paper space, where you can lay out a drawing sheet at its real size (A4 in our case), and set up a scaled view of your drawing on that sheet ready for plotting. Be warned that when you first switch to paper space, your drawing will disappear (since initially your drawing sheet will be blank) ... don’t panic, your drawing is still safe in model space.

The command to switch AutoCAD into paper space is quite obscure: for this tutorial, don’t try to understand the logic of the command, just use it! Once in paper space, you use the Limits command to set the paper size, etc as you did in model space. To do all that, proceed as follows:

To create a scaled view of your drawing, you have to set up a rectangular viewport on the drawing. That is done by entering the Mview command (just type it in followed by ¿). When prompted, pick two points at extreme opposite corners of your drawing sheet to mark the opposite corners of the viewport. Once you have done that, AutoCAD will display your model space drawing inside that viewport.

The next step is to accurately establish the scale of that view inside the viewport. You do that by switching back to model space (with tilemode still turned off) and using the Zoom Scale command as follows ...

Then type in the magnification factor relative to paper space in ONE of the following two forms:

In the first case, this can be read as "one two-hundredths times paper space" and scales it at 1:200 relative to paper space. In the second case, it sets the viewport scale at 1:1. Now use RealTime Pan to position the scaled drawing within the viewport … for reasons you’ll appreciate better in a moment, it is best to position the view in one of the four corners of the viewport.

The next step is to re-size the viewport so that it neatly encloses the drawing view. To do that, simply return to paper space by:

Then use the mouse to select the viewport frame ... it should become highlighted with small red squares (called handles) at each corner. Click on the handle in the corner opposite from where you positioned the drawing and it should become active (and change colour). You can now use the mouse to drag that corner in closer to the drawing so that the viewport tightly encloses it. When you have got it right, click the left mouse button to fix that position.

If you want to hide the rectangular frame around the viewport, then you need to move it to an invisible layer — this does not make the view invisible, only the rectangular frame around the view!. In this instance, the easiest way to do that is to use the Change Properties tool (illustrated) to place it on the construction layer which is already turned off! That process is simple if you just follow the options in the dialogue box.

Finally, use the Text commands described in the last tutorial to add some titles to your drawing (in Paper Space) before going on to plot it as explained in the last section.

The last step in this tutorial is to create a postscript plot file which you can then print on the laser printer located in the laboratory.

You want to plot the full "limits" of your paper space drawing at 1:1 scale. Simply issue the Plot command (or click the Plot button) and examine the plotting dialogue box that appears on the screen. There are a few things in the dialogue that you should change …

• Check that the selected plotter is "Postscript Laser" (and change it if is not!);
• Check that the Plot to File option has been selected and then click the File button … in the resulting dialogue box, enter a file name and make sure it is placed in the Q: drive ready for printing;
• Check that the area to plot is set to limits;
• Set the paper size to A4 (210 x 297) and the Rotation to 90^o (ignoring the strange values for the plot origin … they are necessary to ensure that the drawing is centred on the A4 sheet);
• Set the Scale to 1:1.

Finally, do a "full" Plot Preview and check that the plot looks right on the screen. It will look a little off-centre, but that is because of the strange settings for the plot origin. If the whole drawing is at least visible, then press <Esc> to return to the plot dialogue and then click OK to plot the drawing.

Once you have done that, save and exit from AutoCAD, and then print the plot file on the printer as with any other document (following the instructions on the computer adjacent to the printer).

That concludes the CAD Tutorial!