Engineering drawings and standards
Engineering drawings are a precise language for describing parts and assemblies. Learn why standards exist, which ones you’ll meet and what a complete drawing contains.
In this lesson you will
- Explain the purpose of engineering drawings
- Name the main drafting standards
- List the types of engineering drawings
- Know what every drawing sheet must contain
A precise language
An engineering drawing must let someone else make and inspect a part exactly as intended, without asking questions. That means complete geometry, dimensions with tolerances, materials, finishes and notes — all expressed in conventions everyone reads the same way.
Standards
- ISO 128 — general principles of presentation (lines, views, sections).
- ISO 129 — dimensioning; ISO 1101 — geometrical tolerancing (GPS system).
- ASME Y14.5 — dimensioning and tolerancing in the US; ASME Y14 series for other drawing practices.
- National standards such as AS 1100 (Australia) and BS 8888 (UK) build on ISO.
Your employer or client specifies which apply. Mixing conventions (e.g. projection methods) on one drawing causes errors.
Drawing types
Detail (part) drawings fully define one part. Assembly drawings show how parts fit together, with a bill of materials. Arrangement / general arrangement drawings show layouts of equipment. Schematics show function (e.g. hydraulic or electrical diagrams) rather than physical form.
The sheet
Every sheet has a border and a title block with part name, drawing number, revision, material, scale, projection symbol, units, general tolerances, drawn/checked/approved, date and company. A revision block records changes.
Common mistakes
Mixing ISO and ASME conventions on one drawing.
Pick one standard, state it in the title block and follow it throughout.
Leaving general tolerances unstated.
Add a general tolerance note so every untoleranced dimension has a defined limit.
Missing units.
State units once in the title block (e.g. 'All dimensions in mm').
Exercise
Read a drawing
- Find a published engineering drawing (manufacturers often publish product drawings).
- Identify the standard, projection method, units and general tolerances.
- List every item in the title block.
You should end up with: Familiarity with a real drawing's structure.
Checklist
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Lesson quiz
Which standard is the US reference for dimensioning and tolerancing?
Finished this lesson?
Taking the quiz marks it complete too. Your course page picks up where you stopped.
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