4.At the Specify base point or [Displacement] <Displacement>: prompt, pick the endpoint at the bottom-right corner of the garage. At the Specify second point of displacement or <use first point as displacement>: prompt, move the cursor

to the right until you see the polar tracking tooltip. Click when the tooltip says 6'-0"<0. (If you can’t find it, type 6',0 . If you’re not using Dynamic Input or have Dynamic Input set to absolute coordinates, add the @ symbol first.) This action stretches the garage by 6 feet.

5.Save your drawing. It should look like Figure 10-26.

Figure 10-26: The longer garage.

Using Construction Commands

Four additional commands are commonly used in the process of constructing models. The BREAK command removes sections of objects at points that you specify. JOIN, a new command, joins co-linear lines, polylines, arcs, elliptical arcs, or splines. CHAMFER creates corners, and FILLET creates rounded corners.

Breaking objects

Drawing a long line and then breaking it into two or more shorter lines is often much easier than drawing two separate lines. A common use for BREAK is to break a wall at a door or a window in an architectural floor plan. You specify two points on the object, and the command erases whatever is between those two points. Typically, you use object snaps to specify the points. Sometimes, you can use TRIM to break an object, but if you have no convenient cutting edge, you may find BREAK more efficient.

You can break lines, polylines, splines, xlines, rays, circles, arcs, elliptical arcs, and ellipses.

To break a line, choose Break from the Modify toolbar. You cannot select the object first. The command responds with the Select object: prompt. (Notice that you can only

select one object to break.) At this prompt, you have two choices:

Select the object at one of the break points that you want to create. You then see the

Specify second break point or [First point]: prompt. Because you have already specified the first point, you can now specify the second point. The command breaks the object between the two points.

220 Part II Drawing in Two Dimensions

Select the object by using any method of object selection. You then see the Specify second break point or [First point]: prompt. Right-click and choose First point. At the Specify first break point: prompt, pick the first break point. At the Specify second break point: prompt, pick the second break point. The command breaks the object between the two points.

You can use BREAK to shorten an object. Pick one point on the object where you want the new endpoint to be. Pick the other point past its current endpoint to cut off the object at the point you picked on the object.

Joining objects

The opposite of breaking objects is joining them. The JOIN command lets you join lines, polylines, arcs, elliptical arcs, and splines. The objects must be along the same linear, circular, or elliptical path. The objects can overlap, have a gap between them, or touch end-to-end.

To join objects, choose Join from the Modify toolbar. Follow these prompts:

Select source object: Select the first object that you want to join.

Select lines to join to source: Select the second object. (AutoCAD knows which type of object you’ve selected for the first prompt and inserts it into the second prompt.) You can continue to select other objects. Press Enter to end selection.

AutoCAD joins the objects.

A very nice touch is the ability to close arcs (to circles) and elliptical arcs (to ellipses). If your first object is either type of arc, you see the Select arcs to join to source or [cLose]: prompt. Use the cLose option to close the arc.

STEPS: Breaking and Joining Objects

1.Open ab10-h.dwg from your CD-ROM.

2.Save the file as ab10-09.dwg in your AutoCAD Bible folder. This is a site plan, as shown in Figure 10-27. Turn on OSNAP and set running object snaps for endpoint and intersection.

3.Choose Break from the Modify toolbar. At the Select object: prompt, pick the line at 1. At the Specify second break point or [First point]: prompt, pick

2. This action shortens the line.

4.Repeat the BREAK command. At the Select object: prompt, pick the circle (it’s a maple tree) anywhere along its circumference. At the Specify second break point or [First point]: prompt, right-click and choose First point. At the Specify first break point: prompt, pick the intersection at 3. At the Specify second break point: prompt, pick the intersection at 4 to break the circle.

5.Let’s say that you decide this is a mistake. Choose Join from the Modify toolbar. At the Select source object: prompt, select the circle (tree) that you just broke

into an arc. At the Select arcs to join to source or [cLose]: prompt, right-click and choose cLose. The arc becomes a full circle again.

6.To break the line at 5, follow these prompts:

If you’re using AutoCAD: Turn on Object Snap Tracking by clicking OTRACK on the status bar. Start the BREAK command again. Follow the prompts:

Select object: Pick the line at 5.

Specify second break point or [First point]: Right-click and choose First point.

Specify first break point: Move the cursor to 6 to acquire it as a tracking point. Then move the cursor to the right onto the line you are breaking. When you see the Endpoint: Intersection tooltip, click. (You have no visual confirmation yet that you picked the right point.)

Specify second break point: Move the cursor to 7 to acquire it as a tracking point. Then move the cursor onto the line you are breaking. At the Endpoint: 4'-2 3/4"<0.0000 tooltip, click.

If you’re using AutoCAD LT: Start the BREAK command again. Follow the prompts:

Select object: Pick the line at 5.

Specify second break point or [First point]: Right-click and choose First point.

Specify first break point: Shift+right-click and choose Tracking from the Object Snap shortcut menu.

tracking First tracking point: Pick the endpoint at 6. Next point (Press ENTER to end tracking): Press Shift+A to

temporarily override OSNAP and move the cursor to the right onto the

line you are breaking. Click.

Next point (Press ENTER to end tracking):

Specify second break point: _ Shift+right-click and choose Tracking from the Object Snap shortcut menu.

tracking First tracking point: Pick the endpoint at 7. Next point (Press ENTER to end tracking): Press Shift+A to

temporarily override OSNAP and move the cursor to the right onto the

line you are breaking. Click.

Next point (Press ENTER to end tracking):

222 Part II Drawing in Two Dimensions

3

4 7 5

1

6

2

8

9

Figure 10-27: A site plan.

7.Start the JOIN command. At the Select source object: prompt, select the line at 8. At the Select lines to join to source: prompt, select the line at 9. Press Enter to end selection and join the lines into one.

8.Save your drawing. It should look like Figure 10-28.

Figure 10-28: The edited site plan.

Creating chamfered corners

The CHAMFER command creates corners from two nonparallel lines. You can also chamfer xlines, rays, and polylines. You can simply extend the lines to meet at an intersection (a square corner), or create a beveled edge. If you create a beveled edge, you define the edge by either two distances or one distance and an angle relative to the first line that you’re chamfering. Figure 10-29 shows the elements of a chamfered corner.

Second chamfer distance

Second line

First line

Figure 10-29: A chamfered corner.

Chamfering is a two-step process. First you define how you want to chamfer the corner, specifying either two distances from the corner or a distance and an angle. Then you select the two lines that you want to chamfer.

To chamfer, choose Chamfer from the Modify toolbar. You cannot select objects before the CHAMFER command. The command responds with the (TRIM mode) Current chamfer

Dist1 = 0.0000, Dist2 = 0.0000 Select first line or [Undo/Polyline/Distance/ Angle/Trim/mEthod/Multiple]: prompt. The command starts by listing the current settings. (The CHAMFER command remembers the last-used chamfer data.) You can define two distances from a corner or one distance and an angle:

To define two distances from the corner, right-click and choose Distance. At the

Specify first chamfer distance <0.0000>: prompt, type the first chamfer distance or press Enter to accept the default (which is the last distance that you defined). At the

Specify second chamfer distance <0.0000>: prompt, type the second distance. The default for this is always the first chamfer distance because equal chamfer distances are so common.

224 Part II Drawing in Two Dimensions

To define a distance (from the corner) and an angle, right-click and choose Angle. At the Specify chamfer length on the first line <1.0000>: prompt, enter a distance. This is the same as the first chamfer distance. At the Specify chamfer angle from the first line <0>: prompt, type the angle between the first line and the chamfer line.

Now that you have specified the settings that you want, you’re ready to chamfer. Your distances or distance and angle are displayed as you just specified them. The command repeats the Select first line or [Undo/Polyline/Distance/Angle/Trim/mEthod/Multiple]: prompt. Select the first line. If you aren’t creating a chamfer with equal distances, the order in which you select the lines is important. The command trims the first line selected by the first distance, and the second line selected based on either the second distance or the angle. At the Select second line: prompt, select the second line to chamfer the lines.

If the lines already intersect, the command trims them to create a corner. The pick points on intersecting lines should be on the part of the lines that you want to keep, not on the part of the lines that you want to trim off.

By default, CHAMFER trims the original lines that it chamfers. If you want to keep the full original lines when you add the chamfer line, choose the Trim option and choose No Trim. Use the Multiple option to continue the prompts and chamfer several corners in one command. The new Undo option lets you undo your last chamfer and try again.

STEPS: Chamfering Lines

1.Open ab10-i.dwg from your CD-ROM.

2.Save the file as ab10-10.dwg in your AutoCAD Bible folder. This drawing is a very small section of a “porcupine” mixer, as shown in Figure 10-30.

3.Choose Chamfer from the Modify toolbar. CHAMFER states the current mode and

distances. At the Select first line or [Undo/Polyline/Distance/Angle/ Trim/mEthod/Multiple]: prompt, pick 1 in Figure 10-30. At the Select second line: prompt, pick 2. (If the current distances are not zero, press Shift as you pick 2.)The command chamfers the two lines to make a corner. (If this doesn’t work, you may have the Trim option set to No Trim. Change the setting to Trim and try again.)

4.Repeat the CHAMFER command. Follow the prompts:

Select first line or [Polyline/Distance/Angle/Trim/Method/mUltiple]:

Right-click and choose Angle.

Specify chamfer length on the first line <1>: 9/16 Specify chamfer angle from the first line <0>: 45

2 3

4

1

Figure 10-30: A mechanical drawing showing a small section of a “porcupine” mixer.

5.At the Select first line or [Undo/Polyline/Distance/Angle/Trim/Method/ mUltiple]: prompt, pick 3 in Figure 10-30. At the Select second line: prompt, pick 4. The command chamfers the two lines, as shown in Figure 10-31.

6.Save your drawing.

Figure 10-31: The edited drawing after using the CHAMFER command.

Creating rounded corners

The FILLET command creates rounded corners, replacing part of two lines with an arc. Fillets are often used in mechanical drawings. In certain cases, you can use FILLET instead of the ARC command to create arcs. As with CHAMFER, you can fillet lines, xlines, rays, and polylines — they can even be parallel. You can also fillet circles, arcs, elliptical arcs, and ellipses.

226 Part II Drawing in Two Dimensions

The FILLET command defines the fillet arc by its radius, as shown in Figure 10-32.

Fillet arc

Radius

Arc center

Figure 10-32: A fillet consisting of two lines and an arc.

Like chamfering, filleting is a two-step process. First you define the radius of the fillet arc. Then you select the two lines that you want to fillet. You cannot select objects before the FILLET command.

To fillet, follow these steps:

1.Choose Fillet from the Modify toolbar. The command responds with the Current settings: Mode = TRIM, Radius = 0.0000 Select first object or [Undo/

Polyline/Radius/Trim/Multiple]: prompt.

2.Right-click and choose Radius.

3.At the Specify fillet radius <0.0000>: prompt, type the radius you want. The default is either 0.0000 or the last radius that you specified.

4.The command repeats the Select first object or [Undo/Polyline/Radius/Trim/Multiple]: prompt. Select the first object that you want to fillet.

5.At the Select second object or shift-select to apply corner: prompt, select the second object that you want to fillet. This action creates the fillet.

By default, FILLET trims the original lines that it fillets, but the FILLET command recalls the last setting you used. If you want to keep the full original lines when you create a fillet, rightclick and choose the Trim option, and then choose No Trim.

Filleting with a zero radius gives the same results as chamfering with distances set to zero. (See the previous section on chamfering.) If your existing settings are non-zero, you can press Shift as you select the second object to create a square corner.

The order in which you select the two objects to be filleted is not important. However, where you pick the objects is quite important. If two objects intersect, the command keeps the objects on the same side of the intersection as your pick point and fillets them. Those parts of the objects on the far side of the intersection are erased.

When you fillet arcs and lines, if more than one fillet is possible, FILLET connects the endpoints closest to your pick points. Filleting circles and lines can produce unexpected results. Sometimes you need to experiment to find the proper pick points.

STEPS: Filleting Objects

1.Open ab10-i.dwg from your CD-ROM.

2.Save the file as ab10-11.dwg in your AutoCAD Bible folder. This is the same drawing used in the previous exercise. It is shown in Figure 10-33.

2

1

Figure 10-33: A mechanical drawing showing a small section of a “porcupine” mixer.

3.Choose Fillet from the Modify toolbar. At the Select first object or [Undo/ Polyline/Radius/Trim/Multiple]: prompt, right-click and choose Radius. At

the Specify fillet radius <1/2>: prompt, type 5/8 .

4.At the Select first object or [Undo/Polyline/Radius/Trim/Multiple]: prompt, pick the line at 1 in Figure 10-33. At the Select second object or shift-select to apply corner: prompt, pick the line at 2 to fillet the two lines.

5.Repeat the FILLET command. At the Select first object or [Undo/Polyline/

Radius/Trim/ Multiple]: prompt, right-click and choose Radius. At the Enter fillet radius <5/8>: prompt, type 1/4 .

6.At the Select first object or [Undo/Polyline/Radius/Trim/Multiple]: prompt, right-click and choose mUltiple. Pick the line at 3 in Figure 10-33. At the Select second object or shift-select to apply corner: prompt, pick the line at 4 to fillet the two lines. The prompts continue. This time pick at 5 and 6.

7.If you want, you can connect the two loose lines that the fillets created and create some more fillets in the drawing.