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Engineering Graphics and CAD · Lesson 28 of 35

Drawings from CAD: views, sections, dimensions, annotations

Produce a standards-compliant working drawing directly from a CAD model, integrating all of Part III.

Readiness check

Learning objectives

By the end of this lesson you can:

Generate base, projected, section, auxiliary, and detail views from a model.
Set projection angle and scale on the drawing sheet.
Add model-derived and reference dimensions.
Annotate tolerances, threads, finish, notes, and a title block.
Verify the drawing is complete and standards-aware.

Check your starting point

Five to ten minutes.

If you change the model, should its drawing update automatically or need redrawing?
On a CAD drawing, if a dimension reads the model's value, can you type a different number over it to "correct" it?
Does making a section view on a CAD drawing require you to hand-draw the hatching?

Interpretation.

Q1: Update automatically; CAD drawings are associative to the model. Skill 28.1.
Q2: No; model-derived dimensions are driven by the model. To change the value, change the model. Skill 28.3.
Q3: No; the section and its hatching are generated from the model, though you still choose the cut. Skill 28.1.

You need all of Part III (views, sections, dimensions, tolerances) and L24-L25 (models to draw from).

0 or 1 weak itemsContinue with this lesson.

2 weak itemsReview Lesson 8, Lesson 17, Lesson 24, Lesson 25, then return.

3 or more weak itemsWork through the prerequisite examples before continuing.

The core idea

What it is. A CAD drawing is a documentation sheet generated from a 3D model, showing the views, sections, and annotations that define the part or assembly. It is associative: it updates when the model changes.

Why an engineer needs it. The model holds the geometry, but manufacturing and inspection still work from a drawing (the contract from L1 and L17). CAD makes producing that drawing faster and keeps it in sync with the model, but the engineer still applies Part III judgement: which views, which dimensions, which tolerances.

What problem it solves. It turns a model into a standards-compliant working drawing efficiently, and keeps the drawing consistent with the model.

What goes wrong when it is ignored. Letting CAD auto-place views and dimensions without judgement gives cluttered or incomplete drawings. Overriding a model-derived dimension value makes the drawing lie about the model, a dangerous error.

A simple mechanical example. From the bearing-block model you generate a front view, a top view, and a section through the bore, then add dimensions, the bore fit, the mounting-hole callouts, a flatness control, a finish, a title block, and the projection symbol. The drawing is the model's manufacturing definition.

Key ideas:

View generation: base, projected, section, auxiliary, and detail views come from the model; you choose which (Part I-II judgement).
Projection angle and scale: set on the sheet; the projection symbol states the convention (L5).
Driven versus reference dimensions: model-derived dimensions are driven (they report the model's value and cannot be edited on the drawing); reference dimensions are marked as such. To change a value, change the model.
Annotations: tolerances, fits, threads, finish, geometric controls, notes, and the title block (all of Part III).
Completeness: run the L17 check on the result.

Part 5: Parts, assemblies, and drawings.

Check: explain the decision in your own words before using a CAD command.

The lesson map. Drawings from CAD: views, sections, dimensions, annotations becomes manageable when you move through the four checks in order and verify each result before continuing.

The skills, taught in order

Skill 28.1 - Generate views from the model

Concept. Views, sections, auxiliaries, and details are generated from the model; you choose which. Terminology. Base view, projected view, section view, auxiliary view, detail view. Procedure. Place a base view, project the others, and add sections/auxiliaries/details where the geometry needs them, using Part I-II judgement. Reasoning. Generation is automatic, but view choice is still an engineering decision. Failure mode. Accepting default views that hide or clutter features. Check. Choose the base view and the section a part needs.

Skill 28.2 - Set projection angle and scale

Concept. The sheet has a projection convention and a scale, stated in the title block. Terminology. Projection angle, scale, sheet size. Procedure. Set first- or third-angle, place the projection symbol, and choose a scale that fits the part legibly; state units. Reasoning. The convention and scale let the drawing be read correctly (L5, L7). Failure mode. Missing projection symbol or an illegible scale. Check. State what the projection symbol communicates.

Skill 28.3 - Add driven and reference dimensions

Concept. Model-derived dimensions are driven; to change a value, change the model. Terminology. Driven (model) dimension, reference dimension. Procedure. Place model-derived dimensions (driven); mark any reference dimensions; never override a driven value on the drawing. Reasoning. Driven dimensions keep the drawing truthful to the model. Failure mode. Typing a different value over a driven dimension, making the drawing lie. Check. State how to change a dimension value correctly (change the model).

Skill 28.4 - Annotate and verify completeness

Concept. Add tolerances, fits, threads, finish, controls, notes, and the title block, then check completeness. Terminology. Annotation, title block, completeness check. Procedure. Apply all Part III annotations the part needs, fill the title block, and run the L17 completeness check. Reasoning. A complete, standards-aware drawing is the manufacturing contract. Failure mode. A drawing missing a tolerance, callout, or the title block. Check. Run the L17 completeness check on the drawing.

Worked example 1: a working drawing of the bearing block

Problem. Produce a working drawing of the bearing block from its model: front and top views, a section through the bore, dimensions, the bore fit, the mounting-hole callouts, a title block, and the projection symbol.

Planning. Generate the views, add the section, dimension and annotate, then verify completeness.

Solution.

Views. Place the front view as the base, project the top view, and generate a section through the bore to reveal the internal bore and any shoulder.
Projection and scale. Set the projection convention (say first-angle), place the projection symbol, choose a scale that fits the block legibly, and state millimetres.
Dimensions. Add model-derived (driven) dimensions: overall sizes, bore location, mounting-hole locations, all placed per ISO 129-1 (Part III).
Annotations. Add the bore fit (say H7 for the bearing), the mounting-hole callouts, any flatness control on the base, and the bore finish. Fill the title block (name, number, material, scale, units, projection symbol, revision).
Completeness check. Run the L17 check: every feature has size and location once, with the tolerances, fit, finish, and controls its function needs.
Result. A complete, standards-aware working drawing generated from the model.

Result. A bearing-block working drawing with front, top, and section views, driven dimensions, the bore fit and hole callouts, a flatness control and finish, a filled title block, and the projection symbol, verified complete.

Why the method works. Generating views from the model and adding Part III annotations, then running the completeness check, produces a correct manufacturing definition efficiently.

How to verify independently. Change a model dimension (say the bore diameter): the drawing view and its driven dimension update automatically. Automatic update confirms associativity and that the dimension is driven.

Worked example 2: a part needing an auxiliary and a detail view

Problem. A part has an inclined face with functional holes and a small, dense feature that is hard to read at the sheet scale. Generate an auxiliary view for the inclined face and a detail view for the small feature, place the functional dimensions in the true-shape auxiliary, and run the completeness check. The complication is choosing and placing non-standard views from the model.

Planning. Add an auxiliary (from L10) and a detail (enlarged) view, then dimension functionally and verify.

Solution.

Auxiliary view. Generate an auxiliary view projected from the inclined face so it appears in true shape (L10). Place the inclined-face holes' functional dimensions here, where they are true, not in a foreshortened principal view.
Detail view. Generate a detail view: an enlarged (larger-scale) view of the small, dense feature, labelled with its scale, so it can be read and dimensioned clearly.
Dimensions. Put the inclined-face functional dimensions in the auxiliary (driven from the model), and the small feature's dimensions in the detail view.
Annotations and completeness. Add the remaining tolerances, callouts, and title block, then run the L17 completeness check on the whole drawing.
Result. A drawing whose auxiliary carries the true-shape functional dimensions and whose detail view makes the small feature legible, all model-derived.

Comparison. Dimensioning the inclined face in a principal view would be wrong (foreshortened, from L10); the auxiliary makes it true. Trying to read the small feature at sheet scale would be error-prone; the detail view enlarges it. Choosing the right generated views is still engineering judgement.

Result. The drawing uses a true-shape auxiliary for the inclined-face functional dimensions and an enlarged detail view for the small feature, verified complete; the auxiliary and detail are engineering choices, not automatic ones.

Independent check. Confirm the inclined-face dimensions sit in the auxiliary (true-shape) view and the small feature is dimensioned in the enlarged detail. Correct placement confirms the views were chosen and used properly.

Misconceptions and diagnostics

Misconception	Why it seems reasonable	Why it is wrong	Evidence that reveals it	Correction	Diagnostic question
"Override a drawing dimension to fix a value."	It edits the number directly.	Driven dimensions report the model; overriding makes the drawing lie about the part.	The drawing value disagrees with the model.	Change the model; the driven dimension updates.	"Is this dimension driven by the model?"
"CAD auto-dimensions the drawing correctly."	It can place dimensions automatically.	View and dimension choice is still engineering judgement (Part I-III).	Auto-dimensions clutter or miss functional needs.	Choose views and dimensions deliberately.	"Are these the views and dimensions the part needs?"
"The drawing is optional once there is a model."	The model has the geometry.	Manufacturing and inspection work from the drawing (the contract).	The shop asks for a drawing to build and inspect from.	Produce a complete drawing from the model.	"Where do the maker and inspector read tolerances and notes?"

Practice ladder

Level A - Recognition

Task. On a CAD drawing, identify the view types (base, projected, section, auxiliary, detail) and the driven dimensions. Deliverable. A labelled drawing. Success criteria. At least four view types and driven dimensions identified. Answer guidance. Detail views are enlarged; sections show hatching; auxiliaries show true shape. Common errors. Confusing a detail with a section. Difficulty. Low.

Level B - Guided application

Task. Place scaffolded views and model-derived dimensions on a sheet, with prompts. Deliverable. The drawing with views and dimensions. Success criteria. Correct views; driven dimensions; projection symbol and scale set. Answer guidance. Base view first, then projected and section views. Common errors. Overriding a driven dimension. Difficulty. Medium.

Level C - Independent application

Task. Produce a full working drawing from a supplied model (front, top, section, dimensions, fit, callouts, title block). Deliverable. A complete working drawing. Success criteria. Standards-aware, complete (passes L17), model-derived. Answer guidance. Apply Part III judgement to the generated views. Common errors. Missing a callout or the title block. Difficulty. Medium to high.

Level D - Transfer and design

Task. Take your own P4 or P5 model to a complete, reviewed working drawing, including any needed auxiliary or detail view, and run the L17 completeness check. Deliverable. The working drawing plus a completeness result. Success criteria. All features defined; correct views (incl. auxiliary/detail if needed); passes the completeness check. Answer guidance. Add the views the geometry actually needs. Common errors. Foreshortened dimensions where an auxiliary was needed. Difficulty. High. (Drawing-completion assessment evidence.)

Working with AI, and proving it yourself

Use AI as a tutor

Useful AI support:

Ask it to list the views a described part needs.
Ask it to explain driven versus reference dimensions.
Ask it to generate a drawing-completeness checklist (compare with L17).

Limits:

A text assistant cannot see your drawing or its associativity.
It may suggest overriding a dimension value.

Verify AI output against: the associativity principle (change the model, not the drawing value), Part III standards, and the L17 completeness check.

Prove it yourself

A plausible but incorrect AI answer, and how to catch it. You ask, "The bore dimension on my drawing should be 25, but the model made it 24.9. Can I just type 25 on the drawing?" and the assistant replies: "Yes, edit the drawing dimension to 25 so it reads correctly."

This makes the drawing lie about the model. Detect it with the driven-dimension principle: the dimension reports the model's actual value (24.9), so typing 25 would document a part different from the model, and the made part would be 24.9. The evidence is the mismatch between the drawing value and the model. Correct conclusion: fix the model's bore to 25; the driven dimension then reads 25 truthfully.

Retrieval and spaced review

What does "associative" mean for a CAD drawing?
What still requires engineering judgement when drawing from a model?
What is a driven dimension, and how do you change its value?
Why is the drawing still needed when a model exists?
What views might a part with an inclined face and a small feature need?
How do you verify a CAD drawing is complete?
Cumulative (L10, L17): How do the auxiliary-view and completeness ideas from earlier apply to CAD drawings?
Reconstruction task: From memory, list the elements of the bearing-block working drawing.

Answers. 1: it updates automatically when the model changes. 2: choosing which views, sections, and dimensions the part needs. 3: a model-derived dimension; change its value by changing the model. 4: manufacturing and inspection work from the drawing (the contract), which carries tolerances, notes, and title block. 5: an auxiliary (true shape of the inclined face) and a detail (enlarged small feature). 6: run the L17 completeness check. 7: dimension inclined faces in the true-shape auxiliary, and check every feature is defined once, exactly as on paper.

Suggested review intervals. 1 day, 3 days, 7 days.

Reference mapping and next step

Read further

Onshape docs (Drawings)
Giesecke ch.13
ISO 128/129-1.

Standards details must be checked against the current official edition used by your institution or employer.

Finish the lesson

You can now: generate views, sections, auxiliaries, and details from a model; set projection and scale; add driven dimensions and annotations; and verify completeness.

Self-assessment checklist.

I choose views deliberately, not by default.
I set the projection symbol and scale.
I never override a driven dimension on the drawing.
I dimension inclined faces in an auxiliary.
I run the completeness check on the drawing.

Next lesson: L29 - Revisions, versions, and engineering change. Why it follows: a drawing is rarely final the first time. Next you learn to manage change to models and drawings with versions, revisions, and a change process, so the documentation stays trustworthy over time.

Required files or submissions: submit your Level C working drawing; the mid-course practical and later assessments build on this. Optional extension: in Onshape, make a drawing of your bearing block, change the model, and watch the drawing update.