SECTIONS OF SOLIDS

Full Section View
A full section view is made by passing the imaginary cutting plane completely through the object. As shown in figure 1, all the hidden features intersected by the cutting plane are represented by visible lines in the section view. Surfaces touched by the cutting plane have section lines drawn at a 45-degree angle to the horizontal.  Hidden lines are omitted in all section views unless they must be used to provide a clear understanding of the object. The top view of the section drawing shows the cutting plane line, with arrows pointing in the direction of line of sight to view the sectioned half of the object. In a multi-view drawing, a full-sectioned view is placed in the same position that an unsectioned view would normally occupy, I.e., a front section view would replace the traditional front view.

Figure 1 shows a full section view of an object.

Half Section view
Half sections are created by passing an imaginary cutting plane only halfway through an object. Hidden lines are omitted on both halves of the section view. Hidden lines may be added to the un-sectioned half, for dimensioning or for clarity. External features of the part are drawn on the un-sectioned half of the view. A center line, not an object line, is used to separate the sectioned half from the un-sectioned half of the view. The cutting plane line shown in the top view. The cutting plane line in the top view is bent at 90° and one arrow is drawn to represent the line of sight needed to create the front view in section. Half section views are used most often on parts that are symmetrical, such as cylinders. Also, half sections are commonly used in assembly drawings when external features are also to be shown. figure 2 shows a half section view of an object.

Figure 2 shows the cutting plane passing halfway through an object and one quarter of the object being removed

Visualization of Section Views
Figure 3 is multi-view drawing of a part that may be difficult to visualize in its 3-D form, because of the many hidden lines.

Figure 3  A multi-view drawing of an object

A section view is created by passing an imaginary cutting plane vertically through the center of the part. Figure  is a 3-D representation of the part after it is sectioned. The section view more clearly shows the interior features of the part. In the left corner of the figure,  the cutting plane arrows, in the front view, point to the left, to represent the direction of sight for producing a right side view in full section. The direction of the arrow can also be thought of as pointing toward the half of the object being kept. The right half of the object is "removed" to reveal the interior features of the part. The line of sight for the section view is perpendicular to the cut surfaces, which means they are drawn true size and shape in the section view. Also, no hidden lines are drawn and all visible surfaces and edges behind the cutting plane are drawn as object lines. The corners of the section view are numbered  as shown in the right hand figure so that they can be compared with the orthographic section view.

Figure 4  showing a full section and the physically sectioned plane of the object

The representation of the section view of the object shown in above figure is shown as (b) in next figure . The section view in figure (a) shows only those surfaces touched by the cutting plane. Since conventional practice requires that features behind the cutting plane be represented, the change of planes between the two holes in the counter bored hole are shown in figure (b). If the section is viewed along the line of sight identified by the arrows in figure (c), arcs A, B, and C will be visible and should be represented as lines. In figure (b), the lines are 2-7,4-5,15-14. The counter bore and through holes are represented as rectangular features 2-7-6-3, and 4-5-14-15. All the surfaces touched by the cutting plane are marked with section lines. Because all the surfaces are the same part, the section lines are identical and are drawn in the same direction. The center line is added to the counter bored hole to complete the section view.

CUTTING PLANE LINES: The cutting plane line show the exact line along which the cutting plane passes through the object. This represent the  edge view of the cutting plane and are drawn in the view(s) adjacent to the section view. This is represented in figure 5. In the figure the cutting plane line is drawn in the top view, which is adjacent to the sectioned front view.

Figure 5 showing the representation of a cutting plane line

Cutting plane lines are thick (0.7 mm) dashed lines, that extend past the edge of the object 6 mm and have line segments at each end drawn at 90 degrees and terminated with arrows. The arrows represent the direction of the line of sight for the section view and they point away from the sectioned view. Two types of lines are acceptable for cutting plane lines in multi-view drawings. The normal representation of cutting plane lines are shown in figure 6. Line B-B is composed of alternating long and two  short dashes, which is one of the two standard  methods.  The length of the long dashes varies according to the size of the drawing, and is approximately 20 to 40 mm.  For a very large section view drawing, the long dashes are made very long to save drawing time. The short dashes are approximately 3 mm long.  The open space between the lines is approximately 1.5 mm. Capital letters are placed at each end of the cutting plane line, for clarity or when more than one cutting plane is used on a drawing.  The second method used for cutting plane lines is shown by line C-C, which is composed of equal-length dashed lines. Each dash is approximately 6 mm long, with a 1.5 mm space between.

Figure 6 Normal representation of cutting plane lines.

Placement of Cutting Plane Lines
Cutting plane lines are only added to a drawing for clarity. If the position of the cutting plane is obvious, the line need not be drawn. Also, if the cutting plane line is in the same position as a center line, the cutting plane line has precedence.
In figure 7, the cutting plane appears as an edge in the top view and is normal in the front view; therefore, it is a frontal cutting plane.  The front half of the object is "removed" and the front view is drawn in section. 
If the cutting plane appears as an edge in the front view and is normal in the top view, it is a horizontal cutting plane.  The top half of the object is "removed" and the top view is drawn in section. Figure 7 shows  a horizontal cutting plane.

Figure 7. A horizontal cutting plane.

If the cutting plane appears as an edge in the top and front views and is normal in the profile view, it is a profile cutting plane.  The left (or right) half of the object is "removed" and the left (or right) side view is drawn in section. A profile cutting plane is shown by BB in figure 14. 
Multiple sections can be done on a single object, as shown in the figure 8.  In this example, two cutting planes are used: one a horizontal and the other a profile cutting plane. Both cutting planes appear on edge in the front view, and are represented by cutting plane lines A-A and B-B, respectively. Each cutting plane will create a section view, and each section view is drawn as if the other cutting plane did not exist.

Figure 8. shows a profile cutting plane.

Section Line Practices
Section lines or cross-hatch lines are added to a section view to indicate the surfaces that are cut by the imaginary cutting plane. 
Different section line symbols can be used to represent various types of materials. 
However, there are so many different materials used in engineering design that the general symbol (i.e., the one used for cast iron) may be used for most purposes on engineering drawings. 
The actual type of material required is then noted in the title block or parts list or as a note on the drawing.  The angle at which lines are drawn is usually 45° degrees to the horizontal, but this can be changed for adjacent parts shown in the same section.  Also the spacing between section lines is uniform on a section view.

Material Symbols
The type of section line used to represent a surface varies according to the type of material.  Symbols generally used for various materials are shown in figure 9. However, the general purpose section line symbol used in most section view drawings is that of cast iron. The specific type of steel to be used will be indicated in the title block or parts list. Occasionally, with assembly section views, material symbols are used to identify different parts of the assembly.

Figure 9.  General symbols used to represent various materials  in section view.

Broken-Out Sections
A broken-out section is used when only a portion of the object needs to be sectioned. A broken-out section view of an object is shown in figure 10.  A break line separates the sectioned portion from the un-sectioned portion of the view.  A break line is drawn freehand to represent the jagged edge of the break.  No cutting plane line is drawn. Hidden lines may be omitted from the un-sectioned part of the view, unless necessary for clarity. A broken-out section is also used instead of a half or full section view to save time.

Figure 10 shows the broken out section of an  object. Majority of the technical details are also shown.