01There is always a definition.
A drawing, a 3D model with PMI, or whatever replaces them next — a part is always made and inspected against one definition. What is not defined is a guess.
Guide · Technical drawings
What every technical drawing needs.
A practical checklist for engineering drawings that suppliers can quote, make and inspect without calling you — based on the ISO standards used across Sweden and Europe: title block, projection, dimensioning, tolerances, GD&T, surface roughness, material and welds.
- Part / drawing no.
- Rev.
- Checked by
- Date
Four rules every drawing follows.
02Say it once.
Each dimension is given exactly once, in one place. Repeat it and you have two truths the moment one of them changes. A repeat is only allowed as a reference dimension in brackets.
03Start from the datum.
Dimensions normally start from datums — the functional surfaces the part is located on when it is used and measured. Chained dimensions let errors stack; datum dimensions do not.
04A boxed dimension means GD&T.
A dimension in a box is theoretically exact. It has no ± of its own — its tolerance comes from a geometrical tolerance frame, usually position or profile.
You don’t have to know every standard by heart. You do have to say what you want so clearly that it can be read only one way. Standards are simply the shared language for doing that.
14 topics · 48 checks
The technical drawing checklist
0 / 48 checked
Title block
The title block is how a drawing is found, trusted and traced. A missing owner, number or approval means the supplier is guessing which version is valid.
Views and projection method
First-angle (European) and third-angle (American) place the same views on opposite sides. Without the symbol, a mirrored part is a real risk.
Sections and detail views
Hidden internal features are hard to dimension and easy to misread. A section or an enlarged detail makes them unambiguous.
Scale
Nobody should measure a print, but the scale still tells the reader how big the part is and how detailed the views are.
Units
One forgotten unit note is how a 25.4× error reaches the shop floor.
Dimensioning
Every feature should be defined exactly once, from the surfaces that matter for function — not from wherever the CAD sketch started.
General tolerances
Untoleranced dimensions do not exist. A general tolerance note covers every value without an individual tolerance — and it should be chosen, not copied.
Geometrical tolerances (GD&T)
Size tolerances alone do not control form, orientation or position. GD&T says exactly how the part will be fixtured and measured.
Surface roughness
Roughness drives cost. Ra 0.8 everywhere is expensive; no requirement at all is a gamble on sealing and sliding faces.
Material and surface treatment
A material name like "steel" or "aluminium" can mean dozens of grades with very different strength, weldability and price.
Weld symbols
A weld that is only drawn, not specified, will be made to the welder’s judgement — size, length and quality included.
Revision table
Suppliers keep old prints. A clear revision history is how they know what changed — and whether parts already made are still good.
General notes and final check
The last look before release: is this drawing enough on its own for someone who has never seen the 3D model?
Model-based definition and material inside
When the 3D model replaces the drawing, the rules stay the same — the definition just moves into the model. For printed, lattice or fibre materials, the material is no longer one uniform name.
Free checklist from nordproto* — engineering studio, Skåne, Sweden · info@nordproto.se
From drawings to models — and materials with an inside.
Model-based definition (MBD)
Industry is moving from 2D drawings to the 3D model as the master. Dimensions, GD&T, surface and material data are attached to the geometry as semantic PMI, read directly by CAM and CMM software. The language of tolerancing does not change — only where it is written.
- ISO 16792
- Digital product definition data practices
- ASME Y14.41
- The US equivalent for digital product definition
- ISO 10303-242
- STEP AP242 — exchanging the model with semantic PMI
- ISO 23952
- QIF — quality and inspection data from the same model
- ISO 1101 · ISO 5459
- GPS tolerancing and datums — the same language as on paper
Beyond isotropic materials
A material used to be a name in the title block, with the same properties in every direction. Additive manufacturing, lattices, graded and fibre-reinforced materials end that: we now define the inside of the material — build orientation, layers, lattice cells, density and fibre directions — and properties per direction.
- ISO/ASTM 52900
- Additive manufacturing — terminology and orientation
- ISO/ASTM 52910
- Design for additive manufacturing
- ISO/ASTM 52901
- Requirements for purchased AM parts
- ISO/ASTM 52915
- AMF format — can describe lattices and graded materials
- ASME Y14.46
- Product definition for additive manufacturing
The medium changes. The rule does not. Paper drawing, 3D model or a voxel-by-voxel material map — there is always one definition, and it has to be complete.
Checklista för ritningsunderlag.
Ett bra ritningsunderlag gör att leverantören kan offerera, tillverka och kontrollera detaljen utan frågor. Checklistan ovan går igenom namnruta (ISO 7200), vyer och projektionsmetod, snitt och detaljvyer, skala och enheter, måttsättning (ISO 129-1), allmäntoleranser (ISO 2768), geometriska toleranser (ISO 1101), ytjämnhet (ISO 21920-1), material och ytbehandling, svetssymboler (ISO 2553) och revisionstabell — samt modellbaserad definition (MBD) och material med anisotropa egenskaper, som vid additiv tillverkning. Grundregeln är densamma: varje mått anges en gång, utgår från datum, och det finns alltid en fullständig definition. Vi granskar gärna era ritningar — på svenska, engelska eller turkiska.
Common questions about drawings and tolerances.
What must a technical drawing contain?
At minimum: a title block with owner, number, title, date, approval and units (ISO 7200); enough views to define the part with a projection symbol; complete dimensions (ISO 129-1); a general tolerance (e.g. ISO 2768-m); geometrical tolerances where function needs them (ISO 1101); surface requirements (ISO 21920-1); material and surface treatment; and a revision table.
What is the difference between first-angle and third-angle projection?
In first-angle projection, used in Europe and Sweden, the view seen from the left is placed on the right of the front view. In third-angle projection, common in the USA, it is placed on the left. The same part therefore looks mirrored between the two, which is why the projection symbol must always be on the drawing.
What does ISO 2768-mK mean on a drawing?
It is a general tolerance note. "m" is the medium class of ISO 2768-1 for linear and angular dimensions without an individual tolerance; "K" is the middle class of ISO 2768-2 for general geometrical tolerances such as straightness and perpendicularity. ISO 2768-2 has been superseded by ISO 22081, so new drawings should state which system they invoke.
Does ISO 21920 replace ISO 1302?
Yes. ISO 21920-1:2021 replaced ISO 1302:2002 for indicating surface texture on drawings. The basic symbol is similar, but parameter notation and defaults have changed, so older drawings should be read with the standard they were made under.
Does every drawing need GD&T?
No. Simple, non-critical parts can be fully defined with dimensions and a general tolerance. GD&T is worth adding where form, orientation or position affects fit and function — hole patterns, bearing seats, mating faces — and where a part must be measured the same way by you and your supplier.
What is model-based definition (MBD)?
In MBD the 3D CAD model, with semantic PMI — dimensions, GD&T, surface and material data attached to the geometry — is the authoritative definition instead of a 2D drawing. Key standards are ISO 16792 (ASME Y14.41 in the US), STEP AP242 (ISO 10303-242) for exchanging the model with its PMI, and QIF (ISO 23952) for inspection. The tolerancing language, ISO 1101, stays the same.
How do you specify additively manufactured or anisotropic parts?
By defining the inside of the material, not just its name: build orientation, properties per direction, lattice type and density, and any graded or fibre-oriented regions. Useful references are ISO/ASTM 52900 (terminology), ISO/ASTM 52910 (design for AM), ISO/ASTM 52901 (requirements for purchased AM parts), ISO/ASTM 52915 (AMF, which can describe lattices and graded materials) and ASME Y14.46.
Do I need to know every standard to make a good drawing?
No. Nobody knows them all by heart. What matters is stating what you want so it can be read only one way: every dimension once, from the datums, with tolerances that follow function. Standards are the shared language that makes that possible.
Vad ska ett ritningsunderlag innehålla?
Namnruta enligt ISO 7200, tillräckliga vyer med projektionssymbol, fullständig måttsättning enligt ISO 129-1, allmäntoleranser (t.ex. ISO 2768-m), geometriska toleranser där funktionen kräver det (ISO 1101), krav på ytjämnhet (ISO 21920-1), material och ytbehandling, svetssymboler enligt ISO 2553 samt en revisionstabell.
Drawing check
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