Dimensioning

Why do we use Dimensions?

Size

andLocation

of all features

Engineers, designers, and engineering technologists need to know

What is Dimensioning?

• Placing numbers (MEASUREMENTS) on a drawing

• Those numbers show SIZE & LOCATION

• SIZE shows how big or small a feature is

• LOCATION explains exactly where something exists in a view

• Remember, we draw three views: the front view, top view, and side view

How do we Dimension?

• It is important to try to include enough dimensions on a drawing to adequately describe an object (but not too many)

• It is also very important we locate those dimensions in the CORRECT place

• Most dimensions should be drawn between views (between the front and top views or between the front and side views)

How to Dimension

• We will need lines with arrows that show length or size of something on a view

• We will need a spot for those arrows to point (beginning and ending spots)

• We will need to place a measurement on our drawing within that arrow

• We need to put all this information in the best possible (correct) location on our drawing

Dimension Completely

Width

Dimension Completely

Height

Width

What “three” Dimensions?

Depth

Width

Height

Three types of LINES used…

• There are mainly three types of lines used when drawing dimensions

• EXTENSION LINES

• DIMENSION LINES

• LEADER LINES

• Notice the explanations on the next slides

Extension Lines…

• Extension lines are the lines that stick out from a corner or edge of a view

• Look at the drawing again and pay close attention to the examples of extension lines that “extend” out from a corner but DO NOT TOUCH any construction line

• This is where the “arrows” will point (touch)

Dimension Line “Types” again:

Dimension Line Extension Line

Leader Line

Dimension Lines…

• Now, look at the lines with the arrows on each end

• These lines are drawn from extension line to extension line

• These “dimension lines” often have a number in the middle (the distance shown)

• Notice the dimension lines in the next slide

Dimension Line “Types” again:

Dimension Line Extension Line

Leader Line

Leader Lines…

• Leader lines are not used as frequently, but they are still important

• Notice where it points

• Notice what it is showing

• Look at the slide again and pay close attention to how each line is used

Dimension Line “Types” again:

Dimension Line Extension Line

Leader Line

Next:Dimensioning Guidelines (Rules)

• Incorrect dimensions will be shown in RED

• Correct dimensions will be shown in GREEN

1) Dimensions should NOT be duplicated, nor should the same information be given in two different ways.

Incorrect

1) Dimensions should NOT be duplicated, nor should the same information be given in two different ways.

Correct

2) Dimensions should be attached to the view that best shows the contour (curve, shape) of the feature to be dimensioned.

Incorrect

Take a look at this rule again…

2) Dimensions should be attached to the view that best shows the contour of the feature to be dimensioned.

So, look at the drawing again (next slide).According to this rule, which view SHOULD those red dimensions be “attached to?”

2) Dimensions should be attached to the view that best shows the contour (curve, shape) of the feature to be dimensioned.

Incorrect

2) Dimensions should be attached to the view that best shows the contour of the feature to be dimensioned.

Correct

3) Don’t attach dimensions to hidden lines.

Incorrect

3) Don’t attach dimensions to hidden lines.

4) Don’t dimension over or through an object.

Incorrect

4) Don’t dimension over or through an object. (not inside any view)

5) Put dimensions between adjacent views.

Incorrect

5) Put dimensions between adjacent views.

Notice this dimension is not between the views; HOWEVER, this is a better placement than dimensioning to the hidden line in the right side view.

6) A circle is dimensioned by its diameter. An arc is dimensioned by its radius.

7) Holes are located by their centerlines. These lines are often drawn long enough to be used as extension lines.

Incorrect

8) Holes should be located and sized in the view that shows them as a circle.

Correct

8) Holes should be located and sized in the view that shows them as a circle.

Numbers 3 and 4

• Read question 3

• Your instructor may explain this more (Raise your hand if you have a question)

• Peek at the graph paper on the back of your worksheet for clarification

• Look at question 4 (the reverse)

• Take two or three minutes to answer question 3 and question 4

Missing Dimensions

• Look at the next slide and try to figure out where there are some missing dimensions

• Don’t forget the arrows on both ends of your dimension lines when we draw them

• Don’t write them on your paper yet

• Look at the three-view drawing and try to notice (to yourself) where a dimension is missing (#5 on the back of your sheet)

Can you locate where there are three Missing Dimensions?

¼ in. scale or 4 squares = 1 in.

Here They Are

Draw them….

• Draw those three dimensions on your paper when that slide is repeated (next)

• The next slide will show the missing dimensions again

• Do your best to put them on your drawing as neatly and correctly as possible

• You will have to squeeze one of them between two other dimensions

Here They Are

Practice Dimensioning…¼ in. scale or 4 squares = 1 in.

Check Your Answers

Directions for next two pages:

• Next, for each isometric sketch on the next few pages you will need to create orthographic drawings (front view, top view, and side view)

…and dimension them.

You will complete three examples.

…more…

• Make sure you place the front view in the lower left corner, the top view directly above the front view in the upper left corner, and the right side view to the right of the front view in the lower right corner.

Begin.• Line up your sketches both

horizontally and vertically.

• Add all of the dimensions necessary using the scale 1 square = ¼ in.

• Your dimension lines should have arrows at the end, and the extension lines you draw should not touch your object lines.

Homework?

• Work on these orthographic drawings for the remainder of class.

• Unless your instructor tells you differently, anything you do not finish is homework.

• DO NOT LOSE THIS ASSIGNMENT.

• Do the best you can and good luck.