6-1 Introduction

Sectional views are used in technical drawing to expose internal surfaces. They serve to present additional orthographic views of surfaces that appear as hidden lines in the standard front, top, and side orthographic views.

Figure 6-1 shows an object intersected by a cutting plane. Figure 6-2 shows the same object, with its right side and the cutting plane removed. Hatch lines represent the locations on the surfaces where the cutting plane passed through solid material. The front and right-side orthographic views and a sectional view are also shown. Note the similarity between the sectional view and the cut pictorial view in Figure 6-1.

Sectional views do not contain hidden lines, so they are used to clarify orthographic views that are difficult to understand because of excessive hidden lines. Figure 6-3 shows an object with a complex internal shape. The standard right view contains many hidden lines and is difficult to follow. Note how much easier it is to understand the object’s internal shape when it is presented as a sectional view.

Sectional views do include all lines that are directly visible. Figure 6-4 shows an object, a cutting plane line, and a sectional view taken along the cutting plane line. Surfaces that are directly visible are shown in the sectional view. For example, part of the large hole in the back left surface is, from the given sectional view’s orientation, blocked by the shorter rectangular surface. The part of the hole that appears above the blocking surface is shown; the part behind the surface is not.

Sectional views are always viewed in the direction defined by the cutting plane arrows. Any surface that is behind the cutting plane is not included in the sectional view. Sectional views are aligned and oriented relative to the cutting plane lines as a side orthographic view is to the front view. The orientation of a sectional view may be better understood by placing your right hand on the cutting plane line so that your thumb is pointing up. Move your hand to the right and place it palm down. Your thumb should now be pointing to the left. Your thumb indicates the top of the view.

Drafters and designers often refer to sectional views as “sectional cuts” or simply “cuts.” The terminology is helpful in understanding how sectional views are defined and created.

6-2 Cutting Plane Lines

Cutting plane lines are used to define the location for the sectional view’s cutting plane. An object is “cut” along a cutting plane line.

Figure 6-5 shows two linetype patterns for cutting plane lines. Either pattern is acceptable, although some companies prefer to use only one linetype for all drawings to ensure a uniform appearance in all of their drawings. The dashed-line pattern is used throughout this book.

The two patterns shown in Figure 6-5 are included in AutoCAD’s linetype library as the Dashed and Phantom styles. The arrow portion of the cutting plane line is created by the use of the Multileader tool, found on the Leaders panel of the Annotate tab or on the Annotation panel of the Home tab.

Drawing a Cutting Plane Line—Method I

Change a given continuous line, A–A, to a cutting plane line (Figure 6-6). The Dashed linetype must first be added to the list of available linetypes.

1. Type the word linetype at a command prompt.

   The Linetype Manager dialog box appears.

2. Select Load.

   The Load or Reload Linetypes dialog box appears (Figure 6-7).

   

3. Select DASHED and PHANTOM and then return to the drawing screen.

4. Click line A–A.

   A Properties dialog box appears.

5. Select the Linetype line in the Properties dialog box.

6. Scroll down the linetype listing and select the DASHED option.

7. Close the Properties dialog box, and press the Esc key.

Drawing an Arrowhead

1. Click the Multileader tool and draw a leader line on the drawing screen (Figure 6-8 (a)). Type any letter in the text prompt; you can edit it later.

   It is recommended that the leader line be either horizontal or vertical. In this example, a vertical line is drawn.

   

2. Click Explode on the Modify panel and explode the leader line.

3. Use the Erase tool from the Modify panel to remove the short horizontal section of the line. Move the letter from the leader to a suitable place near the arrow (Figure 6-8 (b)).

4. Use Move and Copy to create two leader lines and position them at the ends of the dashed section line (Figure 6-8 (c)).

   If necessary, use the Rotate command to align the arrowhead and line segment with the sectional line.

Changing the Size of an Arrowhead

Arrowheads used for cutting plane lines are usually drawn larger than arrowheads used for dimension lines. This serves to make them more distinctive and easier to find. The normal arrowhead size is twice that of a dimension or regular multileader arrow. When creating section arrows with the Multileader tool, it’s most efficient to create a new multileader style to be used for section marks only.

1. Select the Multileader Style Manager from the Leaders panel under the Annotate tab.

   The Multileader Style Manager is accessed by clicking the arrow in the lower-right corner of the Leaders panel.

2. Click New.

   The Create New Multileader Style dialog box appears (Figure 6-9).

3. Enter the new style name SectionMark and click Continue.

   

   The Modify Multileader Style: SectionMark dialog box appears (Figure 6-10).

4. Select the Leader Format tab and use the Arrowhead Size box to change the arrowhead’s size to 0.3600 (from the default arrow size 0.1800). Click OK.

5. Return to the drawing screen and use the Multileader tool to create the needed section marks.

Drawing a Cutting Plane Line—Method II

A cutting plane can also be created by first defining a separate layer for cutting plane lines. The linetype is Dashed or Phantom, and a color can be assigned, if desired. (Colors do not display on black-and-white prints, but they can help you when working on the screen.) Section 3-24 describes how to create and work with layers.

Drawing Cutting Plane Lines

Cutting plane lines should extend beyond the edges of the object (refer to Figures 6-1, 6-2, and 6-3). A cutting plane line should extend far enough beyond the edges of the object so that there is a clear gap between the arrowhead and the edge of the object.

If an object is symmetrical about the centerline and only one sectional view is to be taken, exactly aligned with the centerline, the cutting plane line may be omitted (Figure 6-11).

6-3 Indicating Solid Cuts

Hatching (sometimes called cross-hatching) is used to represent areas where solid material has been cut in a sectional view. Hatch lines are evenly spaced at any inclined angle that is not parallel to any existing edge line and should be visually distinct from the continuous lines that define the boundary of the sectional view.

Figure 6-12 shows an area that includes uniform section lines evenly spaced at 45°. The other area shown in Figure 6-12 includes a 45° edge line; therefore, the section lines cannot be drawn at 45°. Lines at 135° (0° is horizontal to the right) were drawn instead.

Figure 6-13 shows an object that contains edge lines at both 45° and 135°. The section lines within this area were drawn at 60°.

If two or more parts are included within the same sectional view, each part must have visually different section lines. Figure 6-14 shows a sectional view that contains two parts. Part 1’s section lines were spaced 3 millimeters apart at 45°; part 2’s were spaced 3 millimeters apart at 135° (that is, –45°).

The recommended spacing for hatch lines is 0.125 inch, or 3 millimeters, but smaller areas may use section lines spaced closer together than larger areas (Figure 6-15). Section lines should never be spaced so close together as to look blurry or be so far apart that they are not clearly recognizable as section lines.

Evenly spaced sectional line patterns drawn at 45° are called general or uniform patterns; other patterns are available. Different section line patterns are used to help distinguish different materials. The different patterns allow the drawing reader to see what materials are used in a design without having to refer to the drawing’s parts list. It should be noted that not all companies use different patterns to define material differences. When you are in doubt, the general pattern is usually acceptable.

How to draw different hatch patterns in AutoCAD is explained in the next section.

6-4 Hatch

Solid areas cut by section planes are drawn in AutoCAD with the Hatch tool, located in the Draw panel on the Home tab. Hatch offers many different hatch patterns and spacings. The general pattern of evenly spaced lines at 45° is defined as pattern ANSI31 and is the default setting for the Hatch command.

Hatching a Given Area

Given an area, use Hatch to indicate cut surfaces of solids.

1. Select the Hatch tool from the Draw panel.

   The Hatch Creation contextual tab, with its own panels, appears at the end of the ribbon (Figure 6-16).

   

2. Select a point within the area to be hatched and click the mouse.

3. Right-click and select the Enter option.

   The area is hatched (Figure 6-17).

Changing Hatch Patterns

1. Select Hatch from the Draw panel.

   The Hatch Creation contextual tab appears.

2. Click Hatch Pattern. If you see several patterns (which you may, depending on your screen resolution), click the lowest arrow on the right side of the Pattern panel.

   A selection of hatch patterns appears (Figure 6-18). Additional patterns can be found by scrolling down on the right side of the panel.

3. Select the desired pattern and apply it as described previously.

Figure 6-19 shows three intersecting shapes with five different hatch patterns applied.

Changing the Spacing and Angle of a Hatch Pattern

1. Select the Hatch tool from the Draw panel.

   The Hatch Creation contextual tab appears (Figure 6-20).

   

2. Change the Angle option box to 15 and the Scale option box to 2.

   Figure 6-21 shows a comparison between an ANSI31 pattern created with the default values 1 and 0° and the adjusted pattern with the values 2 and 20°.

6-5 Drawing Problem

Figure 6-22 shows an object with a section mark indicating a cutting plane line. Figure 6-23 shows how a front view and a sectional view of the object are created.

1. Draw the front orthographic view of the object and lay out the height and width of the object on the basis of the given dimensions.

   Sectional views must be directly aligned with the angle of the cutting plane line. Sectional views are, in fact, orthographic views that are based on the angle of the cutting plane line. Information is projected to sectional views as it was projected to top and side views. In this example, the cutting plane line is a vertical line, so horizontal projection lines are used to draw the sectional view.

   

   

2. Draw the object features. No hidden lines are drawn.

3. Use Hatch to draw section lines within the appropriate areas.

4. Erase or trim any excess lines.

5. Modify the color of the section lines, if desired.

6. Save the drawing, if desired.

6-6 Styles of Section Lines

AutoCAD has more than 50 different hatch patterns. You can preview the different patterns in swatches in the Hatch Creation tab’s Hatch Pattern panel. Most of the available patterns (in particular the ones starting with AR-) are for architectural use. The patterns can be used to create elevation drawings and to add texture patterns to drawings of houses, buildings, and other structures. Mechanical drawings usually refer to objects made from steel, aluminum, or a composite material. There are hundreds of variations of each of these materials.

In general, if you decide to assign a particular pattern to a material, clearly state which pattern has been assigned to which material on the drawing. This is best done by including a note on the drawing that includes a picture of the pattern and the material that it is to represent. Figure 6-24 shows a drawing note for a hatch pattern used to represent SAE 1040 steel. The representation is unique for the drawing shown.

6-7 Sectional View Location

Sectional views should be located on a drawing behind the arrows. The arrows represent the viewing direction for the sectional view (Figure 6-25). If it is impossible to locate sectional views behind the arrows, they may be located above or below, but still behind, the arrowed portion of the cutting plane line. Sectional views should never be located in front of the arrows.

Sectional views located on a different drawing sheet from the cutting plane line must be cross-referenced to the appropriate cutting plane line (Figure 6-26). The boxed notation C/3 SHT2 next to the cutting plane line means that the sectional view may be found in zone C/3 on sheet 2 of the drawing.

The reference numbers and letters are based on a drawing area charting system similar to that used for locating features on maps. A sectional view located at C/3 SHT2 can be found by going to sheet 2 of the drawing and then drawing a vertical line from the box marked 3 at the top or bottom of the drawing and a horizontal line from the box marked C on the left or right edge of the drawing. The sectional view should be located somewhere near the intersection of the two lines.

6-8 Holes in Sections

Figure 6-27 shows a sectional view of an object that contains three holes. As with orthographic views, a conical point must be included on holes that do not completely penetrate the object.

A common mistake is to omit the back edge of a hole when drawing a sectional view. Figure 6-27 shows a hole drilled through an object. Note that the sectional view includes a straight line across the top and bottom edges of the view that represents the back edges of the hole.

Figure 6-28 shows a counterbored hole, a countersunk hole, a spotface, and a hole through a boss. Remember that any hole that does not completely penetrate the object must include a conical point.

6-9 Gradients

In AutoCAD, a gradient is shading that varies in intensity. Figure 6-29 shows a rectangular shape with two internal circles. The figure also shows the same shape with various gradients added.

Creating a Gradient

1. Select the Gradient tool from the Draw panel.

   The Hatch Creation contextual tab appears, with a default gradient selected and a number of additional patterns available (Figure 6-30).

2. Click a point within the area to which to apply the gradient.

3. Right-click and select the Enter option.

The gradient’s pattern, color, angle, and density, among other properties, are controlled through the Hatch Creation contextual tab.

6-10 Offset Sections

Cutting plane lines need not be drawn as straight lines across the surface of an object. They may be stepped so that more features can be included in the sectional view. In the object shown in Figure 6-31, the cutting plane line crosses two holes and a directly visible open surface that contains a hole. There is no indication in the sectional view that the cutting plane line has been offset.

Cutting plane lines should be placed to include as many features as possible without causing confusion. The goal in using sectional views is to simplify views and to clarify the drawing. Several features can be included on the same cutting plane line so that fewer views are used, giving the drawing a less cluttered look and making it easier for the reader to understand the shape of the object’s features.

Figure 6-32 shows another example of an offset cutting plane line.

6-11 Multiple Sections

More than one sectional view may be taken from the same orthographic view. Figure 6-33 shows a drawing that includes three sectional views, all taken from a front view. Each cutting plane line is labeled with a letter. These letters are used to identify the appropriate sectional views. Identifying letters are also placed at the ends of the cutting plane lines, behind the arrowheads, and below the sectional view. They are written in the format SECTION A-A, SECTION B-B, and so on. The abbreviation SECT may also be used (that is, SECT A-A, SECT B-B, and so on).

The letters I, O, and X are generally not used to identify sectional views because they can easily be misread. If more than 23 sectional views are used, the lettering starts again with double letters: AA-AA, BB-BB, and so on.

6-12 Aligned Sections

Cutting plane lines taken at angles on circular shapes may be aligned, as shown in Figure 6-34. Aligning the sectional views prevents the foreshortening that would result if the view were projected from the original cutting plane line location. A foreshortened view would not present an accurate picture of the object’s surfaces.

6-13 Drawing Conventions in Sections

Slots and small holes that penetrate cylindrical surfaces may be drawn as straight lines, as shown in Figure 6-35. Larger holes—that is, holes whose diameters are greater than the radii of their cylinders—should be drawn showing an elliptical curvature.

Intersecting holes are represented by crossed lines, as shown in Figure 6-36. The crossed lines are drawn from the intersecting corners of the holes.

6-14 Half, Partial, and Broken-Out Sectional Views

Half and partial sectional views allow a designer to show an object by an orthographic view and a sectional view within one view. A half-sectional view is shown in Figure 6-37. Half of the view is a sectional view; the other half is a normal orthographic view, including hidden lines. The cutting plane line is drawn as shown and includes an arrowhead at only one end of the line.

Figure 6-38 shows a partial sectional view. It is similar to a half-sectional view, but the sectional view is taken at a location other than directly on a centerline or one defined by a cutting plane line. A broken line is used to separate the sectional view from the orthographic view. A broken line is a freehand line drawn using the Polyline command.

Broken-out sectional views are like small partial views. They are used to show only small internal portions of an object. Figure 6-39 shows a broken-out sectional view. Broken lines are used to separate the broken-out section from the rest of the orthographic views.

6-15 Removed Sectional Views

Removed sectional views are used to show how an object’s shape changes over its length. Removed sectional views are most often used with long objects whose shape changes continuously over its length (Figure 6-40). The sectional views are not positioned behind the arrowheads but are positioned across the drawing as shown; however, the view orientation is the same as it would be if the view were projected from the arrowheads; it is simply located in a different position in the drawing.

It is good practice to identify the cutting plane lines and the sectional views in alphabetical order. This will make it easier for the drawing’s readers to find the sectional views.

6-16 Breaks

It is often convenient to break long continuous shapes so that they take up less drawing space. There are two drawing conventions used to show breaks: freehand lines, which are used for rectangular shapes, and S-breaks, which are used for cylindrical shapes (Figure 6-41). Draw freehand break lines with the Polyline command, as explained in Section 6-14. Instructions for drawing S-breaks follow.

6-17 Sectional Views of Castings

Cast objects are usually designed to include a feature called a rib (Figure 6-43). Ribs add strength and rigidity to an object. Sectional views of ribs do not include complete section lines because they can be misleading to the reader. Ribs are usually narrow, and a large sectioned area gives the impression of a denser and stronger area than is actually on the casting.

There are two conventions used to present sectional views of cast ribs: one that does not draw any section lines on the ribs and one that puts every other section line on the rib. Sectional views of castings that do not include section lines on ribs are created by using Hatch for those areas that are to be hatched.

6-18 Exercise Problems

Draw a complete front view and a sectional view of the objects in Exercise Problems EX6-1 through EX6-4. The cutting plane line is located on the vertical centerline of the object.

EX6-1 Millimeters

EX6-2 Millimeters

EX6-3 Inches

EX6-4 Millimeters

EX6-5

Draw the following sectional views, using the given dimensions.

EX6-6

EX6-7

Redraw the given top view and Section A-A; then sketch Sections B-B, C-C, and D-D.

Redraw the given front views in Exercise Problems EX6-8 through EX6-11 and replace the given side orthographic view with the appropriate sectional view.

EX6-8

EX6-9

EX6-10 Inches

EX6-11 Inches

Redraw the given front views in Exercise Problems EX6-12 through EX6-15, and replace the given side orthographic view with the appropriate sectional view. The cutting plane is located on the vertical centerlines of the objects.

EX6-12 Inches

EX6-13 Inches

EX6-14 Inches

EX6-15 Millimeters

In Exercise Problems EX6-16 through EX6-19, draw the top orthographic view and the indicated sectional view.

EX6-16 Millimeters

EX6-17 Inches

EX6-18 Millimeters

EX6-19 Millimeters

Redraw the given views and add the specified sectional views in Exercise Problems EX6-20 through EX6-34.

EX6-20 Inches

EX6-21 Inches

EX6-22 Inches

EX6-23 Inches

EX6-24 Inches

Redraw the given front and top views and add Sections A-A, B-B, and C-C, as indicated.

EX6-25 Millimeters

EX6-26 Inches

EX6-27 Inches

EX6-28 Inches

EX6-29 Millimeters

EX6-30 Millimeters

EX6-31 Millimeters

EX6-32 Millimeters

EX6-33 Millimeters

EX6-34 Inches

EX6-35

New customer requirements dictate that a part be redesigned according to the given specifications. Draw a front view and a sectional view of the redesigned part.

1. The diameters of the Ø9 internal access holes are to be increased to Ø12.

2. The diameter of the internal cavity is to be increased to Ø30.

3. The length of the internal cavity is to be increased from 33 to 50.

4. All other sizes and distances are to be increased to maintain the same wall thickness.

EX6-36

An object is to be redesigned as follows:

1. Extend the 1.00-inch vertical slot all the way through the object, creating four corner sections.

2. Locate countersunk holes in each of the four corner sections. Note that two of the corner sections presently have Ø.50 holes. The countersink specifications are Ø.50 – 82°, Ø.75.

3. Locate a Ø.625 hole in the center of the object.

EX6-37

Given the following front, top, and sectional views, create a 2D isometric drawing of the object.

EX6-38

Given the following six views, create a 2D isometric drawing of the object.