Specifications on Part Print

 Specifications on the part print provide information relating to both general and specific characteristics of the workpiece that are not provided within the conventional dimensioning system. Specifications usually pertain to the material, its heat treatment or finish, general tolerance level to be attained, references to other drawings, notations that cannot be included as part of the dimensions, and other instructions. Specifications are either explicit or implied.

Explicit specifications are stated on the part print in sufficient detail to meet fully and completely the instructions required to produce the part. They are the specifications that are actually needed before the part can be made. A specific surface hardness wanted on the part when completed, for example, to be explicit must indicate how hard the surface must be, the depth of the hardness, and the instructions for producing the specification. A few other examples of instructions that must be stated explicitly are:

1. The location of the part number on the workpiece and whether it is to be stamped or produced in the basic process,

2. Surface finish notations,

3. General notes indicating the size of fillets and redii,

4. Treatment of sharp edges, and

5. Areas where treatment of the workpiece is localized and many others.

Implied specifications are those which are not always stated on the part print but are correctly assumed either by general knowledge or convention to be in effect. Generally speaking, such specifications are met in the normal course of manufacturing and are left to the good judgment of the process engineers and the manufacturing people. For example, if a rectangular workpiece 20 × 40 × 60 mm were to be machined, it would be assumed, unless otherwise specified, that the corners would all be square and that it would be unnecessary to specify a 90o angle on each corner. Some specifications are implied from other more specific ones. A hole may have a diameter clearly specified; however, it may not be stated that the hole must be round; this is implied. Although it may not be perfectly round after it is produced, it is assumed that it will be within normal machining tolerances and, therefore, acceptable.

One major danger is created by the implied specification. One can never be certain that the specification is actually implied or has been unintentionally omitted. Because errors of omission are not uncommon, it is always good judgment to check with the product engineer before making a questionable assumption.