8 Sectional Views

Sectional Views

  • CUTTING PLANE
  • CUTTING PLANE LINE
  • SECTION LINING
  • FULL SECTIONS
  • HALF SECTIONS
  • BROKEN OUT SECTIONS
  • REVOLVFD SECTIONS
  • OFFSET SECTIONS
  • REMOVED SECTIONS

You have learned that when making a multiview sketch, hidden edges and surfaces are usually shown with hidden (dash) lines.

When an object becomes more complex, as in the case of an automobile engine block, a clearer presentation of the interior can be made by sketching the object as it would look if it were cut apart. In that way, the many hidden lines on the sketch are eliminated.

The process of sketching the internal configuration of an object by showing it cut apart is known as sectioning. Sectioning is used frequently on a wide variety of Industrial drawings.

In this example, blocks A and B result after the block in figure 1 has been “Sectioned”. When you cut an apple in half you have sectioned it. Just as an apple can be sectioned any way you choose, so can an object in a sectional view of a drawing or sketch.

Example of a sliced block. The image displays a wireframe illustration of three U-shaped objects, each separated from one another. On the left, a block with a rectangular indented central section is shown. In the center, an open rectangular frame is depicted, with similar dimensions to the first block but without a top and bottom. On the right, another similar U-shaped frame is presented, matching the size and shape of the center piece. The lines are black on a white background, and the objects are rendered in a three-dimensional perspective with visible edges and corners.

Cutting Plane
A surface cut by the saw in the drawing above is a cutting plane. Actually, it is an imaginary cutting plane taken through the object, since the object is imagined as being cut through at a desired location.
Cutting Plane Line
A cutting plane is represented on a drawing by a cutting plane line. This is a heavy long-short-short-long kind of line terminated with arrows. The arrows in show the direction of view.

Cutting plane placed in a drawing. The image depicts a technical drawing featuring two concentric rectangles, one inside the other. The outer rectangle is larger, surrounding the smaller inner rectangle. A vertical dashed line, labeled as a "CUTTING PLANE LINE," runs through the center of both rectangles, extending beyond their upper and lower edges. The cutting plane line is accompanied by arrows at both ends pointing outward, indicating the direction of view. A label with an arrow points to the line from the right.

 

Once again, here is an graphic example of a cutting plane line and the section that develops from it.

Use of a cutting plane explained. The image consists of a sequence of three elements, depicting the process of sectioning an object. On the left, there's a three-dimensional rectangular object with a square cut-out in the center, resembling a hollow frame. The middle element shows the same object but with a dashed line and arrows indicating a vertical cutting plane through the object. The right element illustrates the resulting section, revealing a C-shaped cross-section with horizontal lines representing the cut surface.

Section Lining

The lines in the figure above, which look like saw marks, are called section lining. They are found on most sectional views, and indicate the surface which has been exposed by the cutting plane. Notice that the square hole in the object has no section lining, since it was not changed by sectioning.

 

Different kinds of section lining is used to identify different materials. When an object is made of a combination of materials, a variety of section lining symbols makes materials identification easier. Here are a few examples:

 

Hatch patterns use to illustrate the sectioned portion of the view. The image displays five distinct black-and-white patterns arranged horizontally. From left to right: Net - A grid of downward-pointing triangles forming a repetitive, net-like pattern. Brick (first) - Regular and uniform rectangles arranged in horizontal rows, resembling a traditional brick wall. Brick (second) - Rectangles interwoven in a basket-weave pattern, with alternating vertical and horizontal orientation. Honey Comb - Hexagonal shapes tightly packed together, mimicking a honeycomb structure. Stone - Irregular, organic shapes resembling a cluster of uneven stones or cobblestones.

 

Section lines are very light. When sketching an object or part that requires a sectional view, they are drawn by eye at an angle of approximately 45 degrees, and are spaced about 1/8” apart. Since they are used to set off a section, they must be drawn with care.

It is best to use the symbol for the material being shown as a section on a sketch. If that symbol is not known, you may use the general purpose symbol, which is also the symbol for cast iron.

Full Sections

When a cutting plane line passes entirely through an object, the resulting section is called a full section Fig. 7 illustrates a full section.

 

Full section explained. The image contains three diagrams of a mechanical part. The top diagram shows a top view of a rectangular plate with two smaller circles on either end and a larger circle in the center. This is a technical drawing with dashed lines indicating hidden features and dimensions marked with arrows. Below it, a cross-sectional view is depicted, showing the interior structure cut along the dashed lines. The cross-section reveals a cylindrical protrusion extending from the base of the plate. On the right, an isometric view gives a three-dimensional perspective of the same part, highlighting its oval shape and circular features.

 

It is possible to section an object whenever a closer look intentionally is desired. Here is an object sectioned from two different directions.

 

Use of multiple sections in a drawing. The image depicts a technical drawing of an object with different views and sectional diagrams. In the center is a top view of a rectangular object with a circular hole in the middle and labeled dimensions "A-A" and "B-B" indicating sectional planes. On either side of the top view are isometric drawings of the object. On the left, the object is shown from an angled perspective, displaying its three-dimensional form with a semi-circular cut. The right side also shows the object from another angle with similar features. Below the top view are two sectional views labeled "SEC. A-A" and "SEC. B-B." These show detailed cross-sections of the object, highlighting internal structures not visible from the exterior.

Half Sections

If the cutting plane is passed halfway through an object, and one-quarter of the object is removed, the resulting section is a half section.  A half section has the advantage of showing both inside and outside configurations.

It is frequently used for symmetrical objects. Hidden lines are usually not shown on the un-sectioned half unless they are needed for clearness or for dimensioning purposes. As in all sectional drawings, the cutting plane take precedence over the center line.

 

Showing a section line being used in a drawing. The image features a diagram with two main components: a top view and a section view of a geometric object. The top view displays a circle with a dashed centerline and an arrow pointing away from the center. An extended line with an arrow indicates the cutting plane. The section view below shows a trapezoidal shape with parallel top and bottom edges, shaded with diagonal lines. Text annotations explain drafting conventions, specifically that the cutting plane takes precedence over center lines, and that an identification letter is not required if only one section is shown.

 

Here is another example of a half section. Remember that only one fourth of the object is removed with a half section, whereas half of the object is generally removed with a full section.

Half section explained. The image displays a technical drawing of an engineering component, specifically a circular flange. The main view is a top view, showcasing a circular object with concentric circles and four equally spaced bolt holes along its circumference. An arrow indicates a direction on the top view, leading to a section view below it. The section view illustrates the side profile of the flange, detailing the cylindrical structure's height and the thickness of the flange base. A small inset in the top right corner shows a 3D isometric view of the flange, offering a better visual of its cylindrical form. Lines labeled on the drawing include a cutting plane line, center line, and visible line, pointing out different parts of the technical drawing.

 

This manufacturer’s drawing, using both full and half section, illustrates the advantages of sectional views. The different line directions indicate different parts and materials used in the assembly of this valve.

 

Section view of a valve assembly. The image is a technical drawing of a mechanical component labeled as a "Section View." The diagram shows a cross-sectional view of a device, revealing its internal structure. At the top, there is an electromagnet, depicted as a rectangular block with a coil inside. Below the electromagnet, the component has a central bolt that runs vertically through the middle. The diagram illustrates the locking pin mechanism on the right side. On the left, there is a single oil feed section. An integral control valve is also part of the system, located to the lower left. The illustration uses a combination of solid and dashed lines to represent various parts and sections.

 

Quiz

Directions: On a separate sheet of paper, complete the section view.

Graphic showing top and front sectioned view for practice of drawing section view hatching. The image shows a technical drawing of a mechanical part. It consists of three separate views: an isometric view in the top right corner, a top view in the center, and a front view at the bottom. The isometric view illustrates a rectangular block with a circular protrusion on top and two smaller holes on either side. The top view displays a similar layout with one large central circle and two smaller circles aligned horizontally across the rectangle, indicating their positions on the block. The front view shows the part's profile, emphasizing the central elevation where the circular protrusion is located.

 

Broken Out Sections

In many cases only a small part of a view needs to be sectioned in order to show some internal detail. In the figure below, the broken out section is removed by a freehand break line. A cutting plane line does not need to be shown, since the location of the cut is obvious.

 

Broken out section view. The image features a technical drawing of a mechanical component. At the top, there is a circular top view of a flange with four symmetrically placed holes, one at each cardinal point. The circular shape includes a smaller inner circle and appears to have center lines crossing vertically and horizontally. Below this, there is a side view of the same component, showing a cylindrical section with its lower portion shaded. A portion of the cylinder is marked as a "BROKEN OUT SECTION," showing an interior cross-section with visible hatching, indicating the material of the component. This side view also depicts the flange at the bottom, consistent with the top view.

Revolved Sections

A revolved section shows the shape of an object by rotating a section 90 degrees to face the viewer. The three revolved sections illustrated in the spear-like object of figure 12 show the changes that take place in its shape.

 

Section views of a multi sized rod. The image depicts a sequence of geometric shapes aligned horizontally. From left to right, the shapes include a cone, a cylinder with vertical hatching, two elongated convex shapes with concave sides, a hexagon with diagonal hatching, another elongated convex shape, a circle filled with vertical and horizontal hatching, and a half-cylinder. All shapes are outlined in black and are connected by a central horizontal line, giving the impression of a single, continuous structure. The design is symmetrical around the center line and is rendered in black and white.

Offset Sections

An offset section is a means of including in a single section several features of an object that are not in a straight line. To do this, the cutting plane line is bent, or “OFFSET” to pass through the features of the part.

 

Offset cutting plane. The image shows a technical drawing consisting of two views of a mechanical component with a rectangular form. The top view presents a flat, rectangular surface with two concentric circles in the center and a smaller circle on the right side. These circles are intersected by several lines denoting measurements and cutting planes. Arrows indicate a cutting plane offset, which points to the section below. The bottom section view displays the component with a vertical section cutaway. It shows details such as hatching to indicate the material and two holes at the top parallel to the surface. The entire piece is drawn with precision, incorporating technical lines, arrows, and annotations.

Removed Sections

A section removed from its normal projected position in the standard arrangement of views is called a “removed” section. Such sections are labeled SECTION A-A, SECTION B-B, etc., corresponding to the letter designation at the ends of the cutting plane line. Removed sections may be partial sections and are often drawn to a different scale.

 

Multiple section lines and view showing interior features. The image is a technical drawing of a cylindrical mechanical component. On the left, there's a side elevation view showing the cylindrical body with a square flange on the left end. Two section lines, labeled A-A and B-B, indicate where the cross-sections are taken. The section A-A is through the cylindrical body, parallel to its flat flange side; it shows two parallel slots. The cross-section B-B, taken through the center and perpendicular to the cylindrical axis, reveals a cylindrical path at the center with hatched areas indicating solid material around it. The main drawing includes detailed lines and measurements, emphasizing dimensions and internal structure.

Quiz

Directions: Complete the half section view of a separate sheet of paper.

 

Graphic of a roller needing a section line and view to show inner features and detail. The image features a technical drawing displaying three views of a cylindrical object. The top left shows a top view: a circle with concentric circles inside and intersecting lines crossing at the center. The top right illustrates an isometric view of the same object, highlighting its cylindrical form with an inner central hole and tapered inner sides. The bottom left depicts a side view of the cylinder in a cross-sectional manner, revealing the internal structure with dashed lines indicating hidden parts.

 

 

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