CAD foundations · Lesson 12 · Approx. 7 minutes including practice
Assembly structures
An assembly structure explains how components and subassemblies belong together. Stable structure supports BOMs, drawing references and parts catalogues. Model organisation should reflect the agreed product structure and intended deliverable.
Step 1: Product definition
A documentation workflow, not an equipment operating sequence. Animation starts only when you choose Play.
Define what belongs in the assembly
An assembly tree is both a modelling structure and a communication structure. Decide which elements are physical components, subassemblies, purchased units and reference-only geometry. A purchased unit may be shown as one item even when its supplier model contains many bodies. The appropriate breakdown depends on the agreed manufacturing and service deliverables. Preserve a stable identifier for each controlled item so a description change does not break downstream records.
Prepare and check the work
Review suppressed components, configurations and external references before producing a BOM. Confirm quantity rules and the level at which fasteners or consumables are counted. Keep assembly orientation and reference geometry understandable for the receiving team. A tidy feature tree is useful, but it cannot prove that the product structure is correct. Compare it with the customer-approved assembly definition and record departures.
Worked example · demonstration only
A supplier pump model contains twenty internal bodies. The customer buys and replaces the pump as one unit. Listing every body as a separately orderable spare would mislead the service team; represent the approved supply level and retain the supplier reference.
Guided practice and review evidence
Use only a demonstration dataset for this exercise: Draw a two-level product tree with quantities per parent assembly. Before starting, write down the question the finished record should answer and identify the source information you would need on a real job. Keep a separate list of missing inputs. Prepare a first draft, then compare it with the topic-specific checks above. Ask another person to follow your references without explaining them verbally. Record where they hesitate, what information they cannot locate and any different interpretation. Keep a brief review log with four columns: observation, proposed action, responsible reviewer and closure evidence. Revise the example and repeat the information-finding check. Your evidence of completion is the revised demonstration record plus that log, not simply time spent reading. Do not upload client information to the academy or practise on operating equipment.
What good completion looks like
A useful result can be understood by someone who did not prepare it. They can identify its purpose, applicable item, source and review status, and they can distinguish confirmed information from unresolved questions. Pay particular attention to this failure mode: Distinguish a purchased complete unit from its non-serviceable internal parts. Check the output in the format the recipient will use. A native file, spreadsheet and exported PDF can expose different problems. Keep the source revision and the issued output linked, and record any limitations of the handover. On a real project, follow the customer's authorised checking and approval arrangements before the information is used. The knowledge check below tests understanding of this lesson; it does not assess practical competence or authorise regulated work.
Practical workflow
- Establish the source: identify the approved input, document revision and person responsible for its technical content. Record missing information as an open question.
- Prepare a small representative example before applying the approach to a whole project. Check identifiers, units, references and the intended reader’s needs.
- Ask the nominated reviewer to check technical meaning. Capture the response, resolve comments and issue only under the agreed document-control process.
Review checklist
- Can another reader identify the source and applicable revision?
- Are assumptions and unresolved decisions clearly recorded?
- Is there evidence of the required review before issue?
Educational material and demonstration examples. Not accredited training, practical competency assessment or authority to perform regulated work. Use current approved sources and your responsible technical authority on real projects.