Assemblies, constraints & file types
Graphic Communication · Higher · mrkellydt.co.uk
What you're learning in this topic
Learning intention WALT
We are learning about assemblies, constraints & file types, specifically to:
understand
- top-down and bottom-up modelling and sub-assemblies
- STEP, IGES, DXF and 3DS file types
be able to
- assemble components with mate, align and centre axis
- use orientate, offset and tangent constraints to fully constrain an assembly
Success criteria WILF
- I can assemble components with mate, align and centre axis
- I can use orientate, offset and tangent constraints to fully constrain an assembly
- I can explain top-down and bottom-up modelling and sub-assemblies
- I can explain STEP, IGES, DXF and 3DS file types
Assembly constraints
- Mate: two faces brought together, facing each other (touching).
- Align (flush): two faces made level, facing the same way.
- Centre axis (axis to axis): the centre lines of two round features lined up, e.g. a pin in a hole.
Typical order: centre axis to line parts up, then mate to bring faces together, then align to finish. Use the exact terms: the 2024 N5 report says most candidates didn't give "centre axis".
Higher constraints HIGHER
- Orientate (angle): sets the angle between parts, e.g. an arm at 20°.
- Offset: a set distance between faces, e.g. 13 from the inner edge.
- Tangent: a curved face touching another face.
"Fully constrained" means every part is fixed so it cannot move. Assembly questions are worth 4 marks and were more demanding than expected in 2024: state each constraint, which faces or axes, and the size.
Top-down and bottom-up modelling HIGHER
- Bottom-up: each component is modelled separately, then inserted into an assembly and constrained. Changes must be made to each part individually.
- Top-down: parts are modelled within the assembly, referencing each other (e.g. projecting a hole position from one part to another). Changing one part updates the related parts automatically.
- Sub-assembly: a group of parts assembled first and then used in a bigger assembly.
- Stock/library components: standard parts such as screws and bearings inserted from a library.
Producing drawings from CAD
CAD can generate orthographic, sectional and pictorial views straight from the 3D model, so views are always consistent and update when the model changes. Never type over a wrong dimension on a production drawing: fix the model instead. In the assignment an overridden dimension scores 0 for that component.
File types HIGHER
- STEP and IGES: neutral 3D formats that can be opened in almost any CAD software, for sharing models between companies.
- DXF: a 2D drawing exchange format, also a vector format.
- 3DS: a 3D format used for rendering and animation.
- STL files are used for 3D printing.
Key terms
| Mate | Two faces brought together facing each other. |
|---|---|
| Align | Two faces made flush, facing the same way. |
| Centre axis | Lines up the axes of two round features. |
| Orientate | Sets an angle between two parts. |
| Offset constraint | Sets a distance between two faces. |
| Top-down modelling | Parts modelled in the assembly referencing each other; changes update automatically. |
| Bottom-up modelling | Parts modelled separately then assembled. |
| STEP / IGES | Neutral 3D file formats that open in most CAD packages. |
Quick check
1. Which constraint lines up a pin with a hole?
- Mate
- Align
- Centre axis
- Fillet
Show answer
2. Two faces touching, facing each other, is…
- Align
- Shell
- Centre axis
- Mate
Show answer
3. Two faces level with each other, facing the same way, is…
- Align
- Mate
- Centre axis
- Chamfer
Show answer
4. Which format would you send to a company using different CAD software?
- JPG
- STEP
- DOCX
- PNG
Show answer
5. Modelling parts inside the assembly so changes update related parts is…
- Bottom-up
- Exploded
- Top-down
- Suppressed
Show answer
Printable worksheet
An I do, we do, you do worksheet for this topic, with a separate answer sheet.