6 Dimensioning

  • Numerals
  • Dimensions
  • Extension Lines
  • Arrowheads
  • Dimension Figures
  • Isometric Dimensioning
  • Orthographic Dimensioning

If a drawing is to be complete, so that the object represented by the drawing can be made as intended by the designer, it must tell two complete stories. It tells this with views, which describe the shape of the object, and with dimensions and notes, which gives sizes and other information needed to make the object.

Therefore, your next step is to learn the basics of dimensioning. In that way you will understand not only how to interpret a drawing to get the information you need, but also how to dimension your sketches so that they can be used to communicate size information to others.

Numerals

It may seem a bit basic, but a few exercises with the shapes of numbers comes before dimensioning. The reason for such review is simply that incorrectly or carelessly made numbers on a drawing or sketch can easily be misinterpreted by someone on the job. That can be costly.

Therefore, the study of numbers forms is justified.

The number forms presented here have been determined to be the most legible, and are used by industry nationwide. The United States standardized 1/8” vertical numbers are correctly formed as follows:

Examples of hand written numbers and fractions.

Dimension Lines

The dimension line is a fine, dark, solid line with arrowheads on each end. It indicates direction and extent of a dimension. In machine sketches and drawings, in which fractions and decimals are used for dimensions, the dimension line is usually broken near the middle to provide open space for the dimension numerals. In architectural and structural sketches and drawings, the numerals are usually above an unbroken dimension line.

 

Examples showing the difference between Engineering and architectural diminishing. The image displays two horizontal dimension lines with arrowheads at both ends, indicating measurements. The top line is labeled "MACHINE DIMENSIONING" with the measurement "30" in the center. Below it, the second line is labeled "ARCHITECTURAL - STRUCTURAL" with the measurement "2'- 6''" in the center. The image uses a simple black and white color scheme.

In either case, the dimension line which is closest to the object should be placed approximately

1/2″ away. The other dimensions beyond the first dimension (if any) should be approximately 3/8″ apart. You do not necessarily have to remember this, but you should remember not to crowd your dimension lines and to keep them a uniform distance apart.

The most important thing is that the drawing needs to be “clean” and dimensions need to be located in a space where they cannot be confused with a surface they are not intended to be used for.

Here is how dimension lines should be sketched:

 

Example of an inner dimension and an outer dimension. The image is a simple black-and-white technical drawing featuring an L-shaped object. The drawing includes dimensions marked with arrows and text annotations. The L-shape's outer horizontal dimension is labeled as 2 1/4 inches, while the inner horizontal dimension is labeled as 1 1/8 inches. The outer vertical dimension, extending upwards from the bottom edge of the L-shape, is labeled as 3/8 inches. The annotation "INNER DIMENSION 1/2 INCH FROM OBJECT" is pointing to the shorter vertical segment. "OUTER DIMENSIONS" points to the longer horizontal segment.

Note: Dimensions less than six feet (72 in.) are given in inches. Dimensions over six feet are usually shown in feet and inches.  Be sure that it is clear how dimensions are called out.  When calling out dimensions that are over 12”, make sure ALL of dimensions are called out in total inches or feet inches throughout the entire drawing.  Either 4’-5” or 53”, they both mean the same thing but if there is a mix of dimensioning it can become easy to look at 4’-8” and see 48”.

Extension Lines

Extension lines on a drawing are fine, dark, solid lines that extend outward from a point on a drawing to which a dimension refers. Usually, the dimension line meets the extension line at right angles. There should be a gap of about 1 / 16″ where the extension line would meet the outline of the object, and the extension line should go beyond the outermost arrowhead approximately 1 /8″. Also, there should be not gaps where extension lines cross. Notice in this example the larger dimensions are correctly placed outside, or beyond the shorter dimensions, and that the dimensions are preferably not drawn on the object itself. Sometimes, however, it is necessary to dimension on the object.

 

Graphic showing the use of extension lines for dimensioning. The image depicts a technical drawing of a geometric shape, resembling a block with a stepped cutout. The shape has various dimensions marked in inches and is drawn with precise lines. The top section of the shape has a horizontal width of 5.00 inches, and within this section, there is a cutout with a width and depth of 2.00 inches each. The entire height of the shape is 6.00 inches. Length indicators show a gap of 1/16 inch between two parallel lines, indicating the space between them. Notes on the drawing advise that extension lines cross without a gap and that the lines should extend by 1/8 inch beyond the visible edges of the shape. The lines are neat and straight, illustrating a clear technical drawing style.

 

It is important to remember to place dimensions on the views, in a two or three view drawing, where they will be the most easily understood. Avoid dimensioning to a hidden line and avoid the duplication of dimensions. Use common sense; keep dimensions as clear and simple as possible. Remember, the person reading your drawing needs to clearly understand, beyond question, how to proceed. Otherwise, costly time and material will be wasted.

There are two basic methods of placing dimensions on a sketch. They may be placed so they read from the bottom of the sketch (unidirectional dimensions) or from the bottom and right side (aligned dimensions). The unidirectional system is usually best, because it is more easily read by workmen.

 

Difference between unidirectional and aligned dimensioning. The image illustrates two methods of dimensioning, labeled as "Unidirectional Dimensioning" and "Aligned Dimensioning." Both sections feature rectangles with measurements indicated by lines and arrows. On the left, in the unidirectional dimensioning section, two rectangles are aligned vertically. The top one is measured at 3½ inches horizontally, and the bottom is 1½ inches vertically, followed by a 2-inch space between. On the right, in the aligned dimensioning section, two rectangles are similarly arranged, with dimensions marked at the top and side, both reading 3½ inches and 2 inches respectively. The dimensions in this section are aligned with the direction of the measurement.

 

When dimensions will not fit in a space in the usual way, other methods are used to dimension clearly, when those crowded conditions exist.

 

Dimension standard and alternative examples.

Angular dimension examples. The image displays three diagrams showcasing different angles, labeled as "Standard Procedure" and "Alternatives A and B." The first diagram on the left represents the "Standard Procedure," featuring a right-angle triangle with an angle of 45 degrees marked inside. To the right, two smaller triangles are labeled as alternatives. "Alternative A" depicts a smaller angle of 15 degrees, while "Alternative B" shows an even smaller angle of 5 degrees. Each triangle is drawn with emphasis on the angle measure, indicated by a curved arrow.

 

Arrowheads

Arrowheads are placed at each end of dimension lines, on leader lines, etc. Correctly made, arrows are about 1/8” to 3/16” in length, and are about three times as long as they are wide. Usually they have a slight barb, much like a fishhook.

To make your drawing look clean, use the same style throughout your drawing or sketch.

 

Correct and incorrect arrowhead examples. The image shows two horizontal lines, each with an arrow at the right end. The top line is labeled "CORRECT" and features a single arrow pointing to the right. The bottom line is labeled "INCORRECT" and has several arrows along its length, pointing to the right. The arrows on the bottom line are spaced out evenly, suggesting a segmented or stepwise progression.

Dimension numerals

Numerals used to dimension an object are normally about 1/8” in height.

Example of numeral size when dimensioning. The image depicts a horizontal line with arrowheads at both ends, indicating a dimension. In the center of the line is the numeral "6." A diagonal leader line points to the numeral, leading to the phrase "NUMERAL 1/8" IN HEIGHT" positioned to the upper right of the numeral. The background is plain and white.

When a dimension includes a fraction, the fraction is approximately 1 / 4″ in height, making the fractional numbers slightly smaller to allow for space above and below the fractional line.

Use of fractional numbers in an dimension. The image depicts a dimension line with arrows at each end, indicating a measurement. In the center of the line, there is the fraction "6 3/4" with a leader line pointing upwards to a text annotation. The annotation reads "FRACTION 1/4" IN HEIGHT," indicating the size of the fraction text.

Again, it is particularly important that the numbers and fractions you may put on a sketch or drawing be legible. Sloppy numbers can cause expensive mistakes.

 

Notes

Notes are used on drawings to provide supplementary information. They should be brief and carefully worded to avoid being misinterpreted, and located on the sketch in an uncrowded area. The leader lines going to the note should be kept short. Notes are usually added after a sketch has been dimensioned to avoid interference with dimensions.

 

Example of using notes in dimensioning. The image shows a technical drawing of a mechanical component with a detailed view from the top and a side profile. The top view features a rectangular object with a rounded corner on the top right. There are two circular marks on this view, one near the rounded corner with an arrow point at it with the notatioin 7/32 DRILL and another closer to the left side with the notation #28 (.1405) DRILL 5/6 DEEP. Lines with arrows extend from these circles, indicating specifications. The side profile shows the same object viewed from the side, depicting the same rounded top and includes annotations. On the top left of the object there is a notation showing depth that reads 1/8 X 45 degrees CHAM. The edge is chamfered at an angle.

 

Quiz

 

Directions: Dimension the examples as indicated.

 

Dimension this 3 ¼ x 6 15/32 rectangle unidirectionally on the top and right sides.

 

Rectangle The image displays a simple line drawing consisting of a rectangle. The overall design has clean, thin black lines on a white background.

 

With a note, show a 5/16 drilled hole.

 

Graphic provided to dimension a hole size. The image displays a simple line drawing consisting of a rectangle with a rounded corner on the bottom right side. Inside the rounded corner, there is a circle placed such that its center aligns with the corner. The circle is crossed by two perpendicular lines, one vertical and one horizontal, extending beyond the circle's boundary, which appears to mark the center point of the circle. The overall design has clean, thin black lines on a white background.

 

Dimension this object. The shorter lines are 3 inches in length.

 

"L" shaped object provided for dimensioning practice. The overall design has clean, thin black lines on a white background.

 

Dimension this object. Use a ruler or scale to determine the line lengths.

 

Graphic to be measured and then properly dimensioned. The image consists of a minimalist black outline of a geometric shape on a white background. The shape resembles a series of connected rectangles and lines, forming a continuous structure. Starting from the top, a short vertical line descends and connects to a longer horizontal line moving to the right. This turns downward into another vertical segment, followed by a horizontal line extending to the left. The shape concludes by enclosing downward with a vertical line parallel to the starting line. The overall form is angular and rigid, with clear right angles.

Oblique Dimensioning

Oblique dimensioning is mostly remembering to avoid dimensioning on the object itself (when possible) and the use of common sense dimensioning principles. It is also usually best to have dimensions read from the bottom (unidirectional) as shown here.

 

Example of oblique dimensioning. The image features a technical drawing consisting of three separate geometric components, each depicted with dimensions and specifications. The top left diagram illustrates a rectangular block with a recessed cutout, displaying dimensions representative of length, width, and depth. The top right sketch depicts an oval shape with two holes, annotations specifying measurements and diameters. The bottom drawing shows a cylindrical rod with dimensions and ends chamfered at 45 degrees.

 

Although it is best not to dimension on the view itself, its usually accepted practice to place diameter and radius dimension on the views if space permits.

Sometime space and time is limited and you might have to bend the typical rules of drawing and dimensioning.  The most important thing is to keep the drawing clean, concise, try to not a repeat dimensions but give all required ones.

Directions: Complete as indicated.

Dimension this three inch cube.

 

Cube to practice oblique dimensioning. The image is a simple line drawing of a three-dimensional cube. It depicts a white cube with thin black outlines, highlighting its edges and corners. The cube is oriented with its front and top faces visible, and the left side face slightly visible as well. The lines are straight and clean, creating a clear representation of a geometric shape.

 

 

The shorter section of this rod is 5/8 inches in diameter by 2 1/8 inches long. The longer section is 7/8 inches in diameter by 3 ½ inches long. Dimension the drawing.

 

Circular lineal part to dimension. The image is a simple black-and-white line drawing of two cylindrical shapes. The larger cylinder is positioned horizontally and partially encloses the smaller cylinder, which extends outward. The smaller cylinder is aligned with the larger one, creating a continuous, elongated shape. The outlines are clean and precise, with no additional details or textures.

 

Isometric Dimensioning

When dimensioning an isometric sketch, it is important to keep dimensions away from the object itself, and to place the dimension on the same plane as the surface of the object being dimensioned. You will probably find that to dimension well in isometric will take some practice.

Example of dimensioning an isometric drawing. The image is a technical drawing of a three-dimensional rectangular wedge with a slanted top surface. The wedge tapers from a wider base to a narrower top. It is depicted in a wireframe style with black lines on a white background. The dimensions of the wedge are marked with arrows and numbers. The front face of the wedge is a rectangle, measuring 1.50 units in height and 1.00 unit in width. The side face is a trapezoid, with a base of 3.00 units and a slanted top edge measuring 0.75 units in width.

Place notes on an isometric drawing without regard to placing them on the same plane, as with dimensions. It is easier to do, and easier to read.

 

Example of placing notes on an isometric drawing. The image depicts a 3D geometric illustration of a block with a circular indentation on the top surface. The block appears rectangular with a square face on top. An arrow points to the edge of the circular indentation, indicating a specific feature with the notation 3/8 REAM. The block is drawn in a simple line art style with no shading, making the edges and shapes clear against the white background.

 

Isometric notes do not have to be on the same plane.

Isometric dimensioning on more than one plane. The image is a technical drawing of a cylindrical mechanical component. It features a central cylindrical body with a flanged end on one side. The drawing includes several dimensions and annotations. The main cylindrical section has a diameter of 1 1/2 inches with a smaller concentric section at one end, which has a diameter of 2 inches. The flanged end on the opposite side has a larger diameter of 3 1/8 inches. The flange extends outward around the base of the cylinder. A dimension line indicates a depth of 3 inches for the component. It also shows a 3/4-inch drill hole through the smaller concentric section.

 

Notice in the example above that part of each leader line to the notes are sketched at an approximate angle of 15, 30, 45, 60 or 75 degrees. This is done to avoid confusion with other lines. Never draw leader lines entirely horizontal or vertical.

 

Isometric dimensioning on a drawing with text, numerical, and angular notations. The image is a technical drawing of a mechanical part viewed in a three-dimensional isometric perspective. It features a block-like structure with a U-shaped cutout on the right side and a circular hole on the left. The block has various dimensions labeled in inches, showing depth, height, and width, including features like the thickness of sections, diameter of holes, and specific angles. The material appears solid and uniform. The technical drawing includes dimension lines, extension lines, and angle measurements indicative of precise engineering design.

Quiz

Directions: complete as indicated.

Dimension this drawing. The dimensions are 3” long, 2 1/8” wide, 1 5/8” high with a 45◦ angle ½” deep. The angle begins as the midpoint of the 3” long dimension.

 

Isometric box with a corner section removed. The image depicts a three-dimensional geometric shape resembling an optical illusion known as a Penrose triangle or impossible triangle. It consists of straight lines forming a continuous triangular path, with the corners connected in such a way that the shape seems to bend in three-dimensional space. The lines are bold and black against a white background, creating a stark contrast that enhances the illusion of the shape. The viewpoint is slightly above and to the side, emphasizing its impossible structure.

 

Dimension this drawing. The base is ½” x 1 ½” square. The cylinder is 1” ∅. x 1-1/8”
long. The drilled through hole is ∅5/8”.

 

 

Cylindrical part attached to a square block with a hole drilled through the center. The image is a simple black-and-white line drawing of a geometric shape. It features a tall, hollow cylindrical object positioned vertically on top of a square base. The cylinder has an open circular top, and the square base has a three-dimensional appearance, suggesting depth with visible bottom and side edges. The drawing employs clean, straight lines and curves, and there is no shading or texturing present.

 

Quiz

 Directions: You will be given an object to sketch and dimension.

Orthographic Dimensioning

When you look at the dovetailed object several pages back, it is easy to see that an isometric sketch can quickly become cluttered with dimensions. Because of this, more complicated sketches and drawings are dimensional in orthographic. This method provides the best way to dimension clearly and in detail.

Here are seven general rules to follow when dimensioning.

  • Show enough dimensions so that the intended sizes can be determined without having a workman calculate or assume any distances.
  • State each dimension clearly, so it is understood in only one way.
  • Show dimensions between points, lines or surfaces which have a necessary relationship to each other or which control the location of other components or mating parts.
  • Select or arrange dimensions to avoid accumulations of dimensions that may cause unsatisfactory mating of parts. (In other words, provide for a buildup of tolerances, as in the example below.

The image is a simple line drawing of a stepped shape consisting of three horizontal sections. The figure appears to be a cross-section of a rectangular block with a notch. The lowest section extends horizontally across the full width of the image. The middle section, slightly narrower, is elevated on the left side. The top section is narrower still, set to the right, forming a step-like design. Dimensions are indicated with arrows and numerical values above the shape. The top of the shape measures 6.00 units in total, with the left section being 2.00 units wide, transitioning into a 2.00 unit wide middle notch.

  • Show each dimension only once. (Do not duplicate dimensions).
  • Where possible, dimension each feature in the view where it appears most clearly, and where its true shape appears.
  • Whenever possible, specify dimensions to make use of readily available materials, parts and tools.

 

Dimensioning example. The image is a technical drawing of a mechanical part, showing both top and side views. The top view is a rectangular shape with a rectangular cutout on the right side. There is a circle near the center of the left side, indicating a hole with a diameter of 1.00. Various dimensions are marked: the overall width of the part is 6.00, with a 3.00 length from the left edge to the center of the hole. The cutout extends 2.00 units vertically and 4.00 units horizontally. The side view shows a layered structure with a thickness of 1.00, and features a smaller section toward the right, which is 0.50 units tall and inset.

 

Notice the dimensions are correctly placed between the views, rather than around the outside edges of the drawing.

 

Quiz

Directions: one a separate piece of paper, make a dimensioned orthographic sketch of this object.

The image is a technical drawing of a U-shaped mechanical component. It is shown in an isometric view, displaying three sides of the object. The base is rectangular, and two vertical walls rise perpendicularly from the base's shorter sides. Each wall has a circular hole in the center, marked with a crosshair for precise location. The dimensions of the component are labeled: the overall width is 2.50 units, the height of the vertical walls is 1.38 units, and the length of the base is 1.75 units. The diameter of each circular hole is 0.50 units, and the thickness of the walls is 0.38 units.

Directions: on a separate piece of paper, make a dimensional orthographic sketch of the object.

The image is a technical drawing of a U-shaped mechanical component. It is shown in an isometric view, displaying three sides of the object. The base is rectangular, and two vertical walls rise perpendicularly from the base's shorter sides. Each wall has a circular hole in the center, marked with a crosshair for precise location. The dimensions of the component are labeled: the overall width is 2.50 units, the height of the vertical walls is 1.38 units, and the length of the base is 1.75 units. The diameter of each circular hole is 0.50 units, and the thickness of the walls is 0.38 units.

Quiz

Directions: You will be given an object to sketch and dimension.

 

 

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