Engineering

Dimension, Extension and Centerlines In Technical Drawings

The technical drawing is a very special area in engineering in which all the people that are dealing with that specific area must read the created technical drawings. The technical drawing is a communication language between the professionals. For example in mechanics, workers, engineers, technicians communicate with each other to tell all the technical aspects of the designed parts or products. A manufacturing worker can find all the information related to the production of the part placed in a technical drawing. 

Technical Drawing with Engineering Graphics

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According to these facts, technical drawings must comply with the standards. There are various kinds of strict standards for creating technical drawings such as ISO or ANSI. All the aspects and details of the technical drawings must comply with them to be understood by all the people around the world. 

So, dimension lines, extension lines, and centerlines have geometric standards in technical drawings. You can find sufficient information about how to use these lines in technical drawings which comply with the standards. 

Dimension Lines In Technical Drawings

Image Source: FREDERICK E. GIESECKE, SHAWNA LOCKHART, Technical Drawing With Engineering Graphics 15th Ed., Pearson, Pg.506.

Dimension lines show the value of the length or angle of the entities of parts or products in technical drawings. Dimension lines are solid and thin lines in which have arrowheads on both ends. The dimension value is located at the center of the dimension line by breaking it. 

The standard sizings of the dimension lines are very important. First of all, the minimum distance between the dimension line and the entity that is to be dimensioned must be 10mm(3/8”). If there are serial dimension lines, the minimum distance between these dimension lines must be 6mm(1/4”). 

The general standard requirements of dimension lines are like that. 

Extension Lines In Technical Drawings

Extension lines are auxiliary lines to show which entity of the part or product is dimensioned with dimension lines and dimension values. Extension lines are solid and thin lines like dimension lines. Extension lines have sizing standards too just like dimension lines. 

Image Source: FREDERICK E. GIESECKE, SHAWNA LOCKHART, Technical Drawing With Engineering Graphics 15th Ed., Pearson, Pg.506.

First of all, extension lines must start from the 1.5mm(1/16”) apart from dimensioned entities of parts and products in technical drawing. And beyond the dimension line, extension lines must extend 3mm(1/8”). These are the general standards of the extension lines. 

Centerlines In Technical Drawings 

Centerlines are the dashed lines to show the symmetrical holes, rounds, and round geometric entities in technical drawings. Alternating long and short dashes are used in centerlines. It is recommended to end the centerlines with long dashes. 

The most important feature of the centerlines is that they can cross all types of lines in technical drawings if it is required. 

Relationship Between Dimension and Extension Lines

Image Source: FREDERICK E. GIESECKE, SHAWNA LOCKHART, Technical Drawing With Engineering Graphics 15th Ed., Pearson, Pg.506.

To obtain a successful dimensioning in technical drawings, you need to be aware of that relationship. 

First of all, the shortest dimension must lie nearest to the object on the technical drawing sheet. With this, you can avoid the crossings between different extension and dimension lines. 

Grouping of the dimension lines on technical drawings will give a better-looking and neat experience to the reader. Group the dimensions as much as possible. 

Conclusion

If you are using CAD software to obtain technical drawings such as Autocad, you can adjust the dimension line settings according to these standards mentioned above. 

As you see, standardizations of the dimension, extension, and centerlines in technical drawings are very simple. 

Do not forget to leave your comments and questions below about the dimension, extension, and centerlines in technical drawings! Your precious feedbacks are very important for us!

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