The Rules of Technical Drawing

Written by jeffery keilholtz
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The Rules of Technical Drawing
Technical drawings are the hallmark of blueprints. (compass on blueprint image by FrankU from

There are many rules and guidelines for creating technical drawings. Mechanical parts and assemblies require clarity and precision in their designs and geometric representations must be exact to build effective machines. Several important guidelines in technical drawing are determined by sheet formatting, dimension rules, and the best overall practices.

Sheet Formats

Sheet formatting is universal in the world of technical drawing. Technical designs include many images and measurements, and setting a basic standard for sheet formatting makes analysing drawings easy and efficient. Notes always go in the upper left-hand corner of a diagram, according to the Franklin W. Olin College of Engineering. Revisions go in the upper right-hand corner and the title block is positioned in the bottom-right. Numbers also run along the top and bottom border and letters run along the sides to identify image zones on a technical drawing.

The Rules of Technical Drawing
Zones help observers identify where additions have been made. (blueprint image by Igor Zhorov from

Dimension Rules

Dimensions must also be clearly marked. When drawing a technical diagram all letters must be capitalised and dimensions cannot be duplicated. According to the Olin School of Engineering, dimension lines cannot cross one another nor should they cross extension lines. It is important to present a front view which best illustrates the object and--unless absolutely necessary--never indicate any hidden lines. Dimensions must also be offset by .38"-inch from the design itself.

The Rules of Technical Drawing
Measurements must be exact when it comes to dimensions. (measurement image by Kimberly Reinick from

Best Practices

It is always best practice to reduce diagram math for the sake of a machinist. Other practice includes the representation of multiple features. If multiples of the same part exist in a technical drawing, feature only one of the dimensions and label that measurement as "NumberX"DIM. This method of identification implies that the dimension is in place "Number" times. For example, as stated on the Olin website, a measurement of "4X .250" indicates that four like dimensions for the measured feature exist within the diagram.

The Rules of Technical Drawing
Use language (including math) that all can understand. (builder and architect image by goce risteski from

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