Basics of Metrology - Real Geometry

Basics of Coordinate Metrology
Unit 6: Basics of Metrology - Real Geometry

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After construction, the part is manufactured on the basis of the technical drawing. This is accompanied by deviations and deformations. They can be caused by the manufacturing machine, the external temperature, material defects and many other effects.

The geometric elements of the manufactured part along with the deviations are called actual shape or real geometric elements.

Real geometry of the
part with manufacture-
related deviations

In addition to the dimensional tolerances, the design engineer can also enter other tolerances in the drawing:

Form tolerances serve for checking the dimensional deviation, in the above example for checking the straightness of all lines of the bottom area lying in parallel to the drawing plane.
Positional tolerances serve for checking the direction, location or runout. A list of all form and position tolerances and the relevant entries on the drawing are shown on the right.

List of the form and position tolerance symbols according to DIN ISO 1101:

Form

	Straightness
	Flatness
	Roundness
	Cylindricity
	Line profile
	Surface profile

Position

	Tilt
	Position
	Coaxiality
	Symmetry
	Parallelism
	Perpendicularity