Tolerance
is the total amount a dimension can vary and is the difference between maximum and minimum values. The total allowable variance in dimensions (upper limit-lower limit)Datum-A datum is a theoretically exact point, axis or plane
Tolerance can measure:
-a physical dimension
-a value or physical property of a material, manufactured object, system, or service
-other values such as temperature and humidity
-in engineering and safety, a physical distance or space
-in mechanical engineering the space between a nut and a bolt
Tolerance may be specified as a factor or percentage of a value.
It is a wide ranfe of allowed values that are specified by a note or published standard with information
Tolerance Symbols
-The tolerance value. If the tolerance zone is circular or cylindrical it is represented with a
-Letters for the datums (code) when the tolerance feature is specified in relation to one, or more datums.
Allowance
-A planned deviation between an actual dimension and a nominal or theoretical dimension. Or between an intermediate-stage dimension and an intended final destination.-This means that the engineer would intentionally make the actual dimensions of an object different from the dimensions of the object on paper
Geometric Tolerancing
This is a symbolic language used on engineering drawings and computer generated 3D solid models for explicitly describing nominal geometry and its allowable variation in form and size
The structure of a welding symbol
- The horizontal line--called the reference line--is the anchor to which all the other welding symbols are tied
- Weld instructions are written along the reference line
- An arrow connects the reference line to the joint that is to be welded.
- The flags growing out of the junction of the reference line and the arrow is present if the weld is to be made in the field during erection of the structure
- When two steel plates are joing together in a T shape, welding may be done on either side of the stem of the T
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