Straightness

Definition

Straightness is a form tolerance that prescribes the largest possible deviation of a line from its geometrical ideal form (Pfeifer and Schmitt 2010). For an axis, the straightness tolerance specifies that the derived median line must lie within some cylindrical zone whose diameter is the specified tolerance. For the line elements of a feature, the straightness tolerance specifies that each line element must lie in a zone bounded by two parallel lines that are separated by the specified tolerance and that are in the cutting plane defining the line element.

Theory and Application

Figure 1 shows an example for a tolerance of spatial straightness. The reference arrow is shown in the extension of the dimension line of the largest cylinder, and therefore the tolerance of straightness is related to the axis of this cylinder. The real axis must be over the whole length within the cylinder with a diameter of the tolerance value, in the example shown 0.06 mm.

Fig. 1

Straightness