It is impossible to manufacture workpieces without deviations from the nominal shape. Workpieces always have deviations of size, form, orientation and location.

When these deviations are too large the usability of the workpiece for its purpose will be impaired. When during manufacturing attempts are made to keep these deviations as small as possible, in order to avoid the impairment of usability, in general the production is too expensive and the product is hard to sell.

In general, competition forces the use of all possibilities for economic production, including possibilities, arising from current developments. Therefore, it is necessary that the drawing tolerances define the workpiece completely, i.e. each property (size, form, orientation and location) must be toleranced. Only then is the manufacturer able to choose the most economic production method, e.g. depending on the number of pieces to be produced and on the production methods available.

Incompletely toleranced drawings result in:

• questions for the production-planning engineer;

• questions for the manufacturing engineer;

• questions for the inspection engineer;

• reworking;

• defects, damages.

Only completely toleranced drawings enable the production of workpieces to be as precise as necessary and as economic as possible. This is necessary for competition.

When all tolerances necessary to define the workpiece completely are indicated individually the drawing becomes overloaded with indications and is hard to read. Therefore general tolerances should be applied.

General tolerances shall be equal to or larger than the customary workshop accuracy. The customary workshop accuracy is equal to those tolerances the workshop does not exceed with...