Line weight and type

What is line weight in drafting? Why is it important? How can it be achieved? Other characteristics of drafting line. Examples

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Svetlana Pencheva: Lecturer Marine Technology

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Line weight

Traditionally Line weight is the thickness of the line i.e. the thinner is the line the lighter it is. But why we need to bother about use of lines with different thicknesses?
Please compare the drawings bellow. It is a fraction of Grey Water System.
Answer: do you read both drawings equally easy and quick?

Standards

Our days businesses around the world try to unify their languages. In case of drafting these are drafting rules, abbreviations and symbols. All this is summarised in Standards. In New Zealand the standard in use is AS1100.101-1992
According to this standard the thicknesses of the lines shall be chosen from one group. For instance if you choose to use the Line group 0.7 mm your lines will be:
Thick line - 0.7mm
Medium line - 0.5mm
Thin line - 0.35mm

Warning!

Be careful when choosing colour of the lines. This characteristic is not covered by standards but can be misleading in your work. Background of Model space is often dark but the printing paper is white! If you have chosen yellow or other light colour when printing this line will almost disappear!

Another advice is to print in black and white. Often the companies use that style of printing. Firstly it is cheaper and secondly this style provides better contrast in most uses of drawings.

Type of lines

Line weight is not the only characteristic of lines used in drawings. Another important characteristic is type of line. Type of line shows the specific pattern of the line. Each type has typical application.
Example:
Continuous thin free-hand line is used fora breaking line
Continuous thin ruled with zig-zag is used as well to show breaking line
Dashed thin line is used to show hidden outlines
Chain thin line is used for centre line
Cain thick line indicates surfaces complying special requirements
Chain thin double dashed outlines alternative and extreme position of movable parts

The rules

These rules are applied not only in hand drawings but in Computer aided drawings as well. AutoCAD offers many ways to do it. Which one to chose depends on the experience of the draughtsmen as well as on the ability to predict possible changes.

You can see an example of AutoCAD image using lines of different type and different weight

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