2.2 Dimensioning

Dimensioning is the process of putting labels on a drawing to indicate how big each feature is.  Dimensions can show the size of a feature or the location of a feature.

Rules for Placing Dimensions

1. Provide information about the size and shape of every feature of of the object.

2. Place dimension on the view that most clearly shows that feature of the object.

3. Provide the over all size in each direction (height, width, depth).  There are rarer situations when the overall dimensions should be left out.

4. Do not provide the same dimension more than once.

5. Do not provide several small dimension that add up to another given dimension (leave one of the smaller dimension off).

6. Dimension lines and leader lines cannot cross extension lines.

7. Avoid placing dimension lines on top of (inside of) the view. Use extension lines so you can place the dimension line next to the view.

8. Avoid dimensioning to hidden lines.  Move the dimension to a view where the edge is visible.

9. Avoid extension lines running through (inside of) the view.  These can get confused with object lines.

10.  Don't put dimensions or hidden lines on isometric views.

Border Lines - Thickest darkest lines on the page.  Used make the lines that enclose the titleblock and drawing space.

Construction Lines - Thin light lines used while creating the drawing, but erased before the drawing is finished.

Object Lines - Solid dark lines used to show the visible edges of an object.

Hidden Lines - Dashed lines that show the location of edges that are not actually visible from that view.  Avoid dimensioning to hidden lines

Center Lines - A series of long-short-long dashes that are used to show the location of the center of a circle, arc, or line of symmetry. Two perpendicular center lines are used to mark the center of a circle or arc forming a small + at the center with longer dashes extending just past the edges of the curve.  When dimensioning the location of a circle, it is common for center line to be extended into a dimension line.

Dimension Line - a line that is the same length as a feature of the object.  Has arrows at each end. Length stated

Extension Line - a line that starts near the object and is co-linear to an edge or feature of the object.

Leader Line -  a line that has one arrow pointing at a feature of the object.  A description is written at the other end.  When used to dimension the diameter or radius of a circle or arc, the arrow and leader line will be perpendicular to the curve.

Finish Mark - a triangular note that is placed next to a surface of the object to indicate it will be made smooth.

        Dimension Lines - These lines are not part of the object but are added to the drawing to make it easier to define the size and location of object features.  Dimension lines are solid and as thin and light as center lines, but always end with arrows (or some other symbol) at each end.  The dimension line will be the same length as the feature of the object it is stating the length of.  Near the middle of the dimension line will be written the stated value for the length.  This could be written next to the dimension line or the writing might be in line with the dimension line (breaking it into two parts).  Whenever possible dimension lines should be placed outside of the object (not inside or over the object) and when possible, avoid the dimension line touching the edge of the object.

      Extension Lines - These lines are not part of the object but  are added to the drawing to make it more clear which feature of the object is being dimensioned.  Extension lines are solid lines that are as thin and light  as center lines.  A standard extension line would start just beyond the edge of the object and extend just a little past the end of the corresponding dimension line that is pointing at it.  Sometimes an extension line will be a continuation of a center line.  Whenever possible, avoid having extension lines that extend into (inside or over) the view of the object.

        Leader Lines - These lines are not part of the object but are added to the drawing to connect a notation to a specific feature of the object.  Leader lines are solid lines that are as thin and light as center lines.  One end of the leader line has an arrow that points to the feature and the notation about the feature will  be at the other end.  Leader lines are often used to dimension the diameter of circles and the radius of arcs.  Details about the shape and depth of holes can also be stated at the end of leader lines.

Chain Dimensioning

Datum (Baseline) Dimensioning

Aligned and Unidirectional Dimensions

Tolerances

Bilateral Tolerances

Unilateral Tolerances

Clearance Fit

Transition Fit

Interference Fit