Technical Drawing Dimensioning: Rules and Annotation Standards

An annotation is the measure of a property of an object which must be specified in a technical drawing. Narrowing, also known as height or size, must meet a set of rules for readability and therefore facilitate the construction of a piece.

• Cota Lines: These are fine lines that indicate the exact size of each part of the piece. Are interrupted at its center for placement of dimensions or measures of that party. Thickness must be thin and an arrowhead. These indicate the beginning and end of each line. Dimension lines to be available so they are outside the contour of the piece.

• Cota Construction Lines: These are solid lines, which starting from the limit order to narrow space. Are drawn perpendicular to the dimension exceeds 1 or 2 mm. If the dimension line is too short to be able to locate the two arrows, be extended on both sides, the auxiliary line outside dimension and draw arrows so that end at right angles.

• Numbers in elevation: Each line is broken to locate in that space the numerical value of the benchmark, ie, go the number of measuring the distance between two given points of the drawing. The number of elevation should be placed, wherever possible, in the middle of the dimension line. Also, when there are several parallel dimension lines are usually alternate the location of their respective benchmark numbers, so they do not appear on top of each other.

Standards bounded

• The number of dimensions in the drawing should be as short as possible, but sufficient to define the size and position of each element of the piece.

• The lower levels should be placed closest to the figure, and higher further away, to avoid crossing between lines and auxiliary dimension.

• The narrow parts of a part that is in the same direction, you should place all dimensions in one continuous line.

• The narrow diameter at the hearing showing a circular shape of the bounded, place a symbol of the diameter before the number of the benchmark.

• The narrow spokes, dimension lines shall have a single arrow, located on the end that touches the arc. Its other end terminates in the center of the arc.

• To narrow a bow, you draw the line concentric with the arch height, and the auxiliary lines are plotted dimension parallel to the bisector of the angle.

• When is an angle that is narrow, the dimension line is an arc of a circle whose center is the vertex of the angle and height are auxiliary lines extending from the sides of the angle.

• Not allowed to use contour lines, axes of symmetry, such as dimension lines, or draw dimension lines as an extension of them.

• If permitted to use axis lines or extensions, as auxiliaries in elevation.