Home / Courses / Engineering Graphics and CAD / Lesson 32

Engineering Graphics and CAD · Lesson 32 of 35

Additive-manufacturing considerations

Understand how design for additive (3D printing) differs from machining, at an introductory level.

Readiness check

Learning objectives

By the end of this lesson you can:

Explain layer-by-layer building and its directionality.
Identify overhangs and the need for support and orientation.
Compare additive and subtractive design freedom and limits.
Recognize anisotropy and minimum feature and wall size.
Choose a print orientation for a part.

Check your starting point

Five to ten minutes.

If a part is built one thin layer at a time from the bottom up, what happens under a feature that overhangs with nothing beneath it?
Would such a part be equally strong in every direction?
Can additive manufacturing make internal shapes that machining cannot reach?

Interpretation.

Q1: It needs support material, or it sags/fails, because there is nothing to build on. Skill 32.2.
Q2: No; layered parts are weaker across the layers (anisotropic). Skill 32.4.
Q3: Yes; additive can build internal geometry that no tool could machine. Skill 32.3.

You need L21 (features) and L30-L31 (other processes) for contrast.

0 or 1 weak itemsContinue with this lesson.

2 weak itemsReview Lesson 21, then return.

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

The core idea

What it is. Additive manufacturing (3D printing) builds a part layer by layer from the bottom up. This gives great geometric freedom (including internal shapes) but introduces constraints: overhangs need support, parts are anisotropic (direction-dependent strength), and orientation trades off finish, strength, and support.

Why an engineer needs it. Additive is now common for prototypes and some production parts, and it follows different design rules from machining and sheet metal. Knowing its freedoms (internal channels, complex shapes) and limits (overhangs, anisotropy, minimum sizes) lets a designer exploit it well.

What problem it solves. It guides designing and orienting parts for additive so they build reliably, with acceptable strength and finish.

What goes wrong when it is ignored. Overhangs printed without support sag or fail; ignoring anisotropy puts weak layer boundaries across the load path; features below the minimum size do not print; a poor orientation wastes support and finish.

A simple mechanical example. An L-bracket printed flat on the build plate needs little support and puts the layers sensibly. Printed on end, an overhanging arm might need support, and the layers might lie across the load, weakening it. The same part, different orientation, very different result.

Key ideas:

Layer building: the part grows in layers; each layer must build on the one below.
Overhangs and support: surfaces that overhang beyond a self-supporting angle (often around 45 degrees from vertical, but process- and material-dependent, so flagged) need support structures, which cost material and leave marks.
Anisotropy: parts are weaker across the layer boundaries than within a layer, so orientation affects strength.
Minimum feature and wall size: very thin walls or tiny features may not print.
Orientation trade-offs: orientation sets which surfaces are smooth, where the layers lie relative to loads, and how much support is needed.
Design freedom: additive can make internal channels and complex shapes impossible to machine.

Part 6: Manufacturability and engineering judgement.

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

The lesson map. Additive-manufacturing considerations becomes manageable when you move through the four checks in order and verify each result before continuing.

The skills, taught in order

Skill 32.1 - Understand layer building and directionality

Concept. The part builds in layers; direction matters. Terminology. Additive manufacturing, layer, build direction. Procedure. Think of the part growing upward in layers; consider how each surface and feature is built relative to the layers. Reasoning. Layering underlies every additive constraint. Failure mode. Ignoring how the part is built up. Check. State the build direction's effect on a horizontal surface versus a vertical wall.

Skill 32.2 - Identify overhangs and support

Concept. Overhangs beyond a self-supporting angle need support. Terminology. Overhang, support structure, self-supporting angle. Procedure. Find surfaces that overhang steeply (roughly beyond 45 degrees from vertical, flagged as process-dependent); expect support there, or reorient/redesign to reduce it. Reasoning. Unsupported overhangs sag or fail. Failure mode. Steep overhangs with no support. Check. Identify an overhang that would need support.

Skill 32.3 - Compare additive and subtractive freedom

Concept. Additive can make shapes machining cannot, within its own limits. Terminology. Design freedom, internal channel. Procedure. Consider whether a shape (internal channel, organic form) is easier additive than machined, while respecting additive limits. Reasoning. Additive's freedom is a design opportunity, used within its constraints. Failure mode. Designing additive parts as if they were machined, missing the freedom or the limits. Check. Name one geometry additive allows that machining cannot.

Skill 32.4 - Account for anisotropy and minimum sizes; choose orientation

Concept. Layered parts are anisotropic and have minimum sizes; orientation trades finish, strength, and support. Terminology. Anisotropy, minimum wall/feature size, print orientation. Procedure. Orient the part so layers lie sensibly relative to loads (not across a critical load path), critical surfaces are smooth, support is minimized, and no feature is below the minimum size. Reasoning. Orientation strongly affects strength, finish, and cost. Failure mode. Orienting with layers across the load path or ignoring minimum sizes. Check. For a loaded part, state a good layer orientation relative to the load.

Worked example 1: choose a print orientation for the L-bracket

Problem. Choose a print orientation for the L-bracket that minimizes support and puts the layers sensibly relative to a load applied to the upright arm.

Planning. Compare orientations for support and for layer direction relative to the load.

Solution.

Load direction. The upright arm carries a load that tends to bend it at the inside corner (where the arm meets the base).
Orientation A, flat on the plate. Lay the bracket so the base is flat on the build plate and the arm rises. The arm's overhang is modest, and the layers build up the arm. The inside corner (the highly stressed region) has layer boundaries roughly across the bending stress, which is a concern for strength.
Orientation B, on its side. Stand the bracket on its side so the L profile faces up. This may increase support under the overhanging arm but can align the layers more favorably along the arm.
Trade-off. Orientation A minimizes support but risks a weak inside corner (layers across the stress); a support-light orientation that also keeps layers along the load is ideal but may not exist for every part. For a lightly loaded bracket, minimizing support (A) is often acceptable; for a load-critical one, favor the orientation that keeps layers along the load even at some support cost.
Choice. For a lightly loaded L-bracket, print flat (Orientation A) to minimize support; for a load-critical one, prioritize layer direction along the load.

Result. Print the lightly loaded L-bracket flat on the base (minimal support); for a load-critical bracket, choose the orientation that keeps the layers along the load at the stressed corner, accepting more support.

Why the method works. Considering both support and layer-versus-load direction picks an orientation that balances buildability and strength.

How to verify independently. Check the chosen orientation: is support minimized, and are the layers not lying across the most stressed region? If both hold (or the trade-off is deliberately chosen), the orientation is justified.

Worked example 2: two orientations of an overhanging boss

Problem. A part has a boss that overhangs the main body. Compare two print orientations: one that leaves the overhang needing support, and one that avoids or reduces it, and weigh support against finish and strength. Note one geometry additive allows that machining cannot. The complication is a multi-factor orientation trade-off.

Planning. Evaluate each orientation for support, finish, and strength, then choose.

Solution.

Orientation 1, overhang unsupported. With the boss overhanging, the underside needs support structures, which cost material and leave a rougher surface where they attach. But this orientation might give a smooth top surface and layers along the main load.
Orientation 2, overhang supported by reorientation. Rotating the part so the boss is built upward (self-supporting) removes the need for support under it, saving material and improving that surface, but it may put a different surface down (needing support there) or lay layers less favorably for load.
Weigh the factors. Support (cost and surface marks), finish (which surfaces must be smooth), and strength (layers relative to load) all shift with orientation. Choose the orientation that best satisfies the part's priorities: if the boss underside is a functional surface, avoid support there; if a different surface is critical, protect that instead.
Additive freedom note. This part could include an internal cooling channel that follows a curved path through the body, which additive can build but machining cannot reach; that is a design opportunity additive uniquely offers.
Choice. Pick the orientation that keeps support off the functional surfaces and layers sensible for the load, accepting support where it least matters.

Comparison. Orientation 1 needs support under the boss (rougher underside) but may favor the top and the load; Orientation 2 avoids that support but shifts the compromise elsewhere. The right choice depends on which surfaces and loads matter most.

Result. Choose the orientation that keeps support off functional surfaces and layers favorable to the load; additive also allows an internal curved channel that machining could not produce.

Independent check. For the chosen orientation, confirm the functional surfaces are support-free and the layers are not across the critical load. Meeting both (or a deliberate trade-off) justifies the choice.

Misconceptions and diagnostics

Misconception	Why it seems reasonable	Why it is wrong	Evidence that reveals it	Correction	Diagnostic question
"Printed parts are isotropic like solid metal bar."	They look solid.	Layered parts are weaker across the layers (anisotropic).	A part breaks along a layer boundary under load.	Orient layers sensibly relative to the load.	"Where do the layers lie relative to the load?"
"Orientation does not matter."	The shape is the same.	Orientation sets support, finish, and strength.	Two orientations give different support and strength.	Choose orientation deliberately.	"What does this orientation trade off?"
"Additive can print anything with no limits."	It is very flexible.	Overhangs need support, and features have minimum sizes.	A steep overhang sags without support.	Respect overhang, support, and minimum-size limits.	"Does this part have unsupported overhangs or tiny features?"

Practice ladder

Level A - Recognition

Task. On six parts, identify overhangs that would need support. Deliverable. Six annotated parts. Success criteria. At least five overhangs correctly identified. Answer guidance. Steep overhangs (beyond roughly 45 degrees from vertical) need support. Common errors. Missing a shallow overhang that is actually fine. Difficulty. Low.

Level B - Guided application

Task. Choose a print orientation for a given part, with prompts on support and layers. Deliverable. An orientation choice with reasons. Success criteria. Support minimized; layers sensible for the load. Answer guidance. Balance support against layer direction. Common errors. Ignoring the load direction. Difficulty. Medium.

Level C - Independent application

Task. Choose and justify a print orientation for a supplied part independently. Deliverable. An orientation with a justification. Success criteria. Support, finish, and strength all considered. Answer guidance. Identify functional surfaces and the load first. Common errors. Optimizing only support. Difficulty. Medium.

Level D - Transfer and design

Task. Redesign a machined feature to exploit additive freedom (for example an internal channel), and state the trade-offs. Deliverable. The redesigned feature plus a trade-off note. Success criteria. The redesign uses additive freedom while respecting its limits; trade-offs stated. Answer guidance. Use internal or organic geometry additive enables. Common errors. Ignoring anisotropy or support in the redesign. Difficulty. Medium to high.

Working with AI, and proving it yourself

Use AI as a tutor

Useful AI support:

Ask it to explain overhangs and support.
Ask it to suggest a print orientation for a described part, then check support and layers.
Ask it to list additive design freedoms and limits.

Limits:

A text assistant may quote a self-supporting angle or minimum size that does not match your printer and material.
It cannot see your part's overhangs.

Verify AI output against: the layer/anisotropy principle, the overhang/support rule, and your printer's and material's actual limits.

Prove it yourself

A plausible but incorrect AI answer, and how to catch it. You ask, "Does it matter which way I orient this loaded printed bracket?" and the assistant replies: "No, orientation does not affect strength; the material is the same."

This ignores anisotropy. Detect it with the layer principle: printed parts are weaker across the layer boundaries, so an orientation that puts layers across the load weakens the part. The evidence is a part failing along a layer line under load. Correct conclusion: orientation strongly affects strength (and support and finish); choose it deliberately relative to the load.

Retrieval and spaced review

How is an additive part built?
Why do overhangs need support?
What does anisotropy mean for a printed part?
What does print orientation trade off?
Name one geometry additive allows that machining cannot.
Why do features have a minimum printable size?
Cumulative (L30-L31): How does additive differ from machining and sheet metal in how material is handled?
Reconstruction task: From memory, explain the orientation trade-off for the L-bracket.

Answers. 1: layer by layer from the bottom up. 2: unsupported overhangs have nothing to build on and sag or fail. 3: it is weaker across the layer boundaries than within a layer. 4: support (cost and surface marks), finish (which surfaces are smooth), and strength (layers relative to load). 5: internal channels or complex organic shapes a tool cannot reach. 6: the process cannot resolve features below a certain size reliably. 7: machining removes material, sheet metal bends a constant-thickness flat, additive builds material up in layers.

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

Reference mapping and next step

Read further

general additive design guidance
links to Manufacturing Processes.

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

Finish the lesson

You can now: explain layer building and directionality; identify overhangs and support; compare additive and subtractive freedom; account for anisotropy and minimum sizes; and choose a print orientation.

Self-assessment checklist.

I think about the build direction and layers.
I identify overhangs that need support.
I orient layers sensibly relative to loads.
I respect minimum feature and wall sizes.
I can use additive freedom (internal shapes) within its limits.

Next lesson: L33 - Design for assembly; recognizing bad geometry. Why it follows: you now understand how parts are made by three processes. L33 turns to how parts go together and how to spot impossible, expensive, or ambiguous geometry, bringing manufacturing judgement to the whole design.

Required files or submissions: submit your Level C orientation justification. Optional extension: take one part and decide the best print orientation, listing what each candidate trades off.

Part VI continues in 19-part6-lessons-cont.md with L33 (Design for assembly; recognizing bad geometry), L34 (Reviewing a model and drawing as an engineer), and L35 (Final integrated project).

# Engineering Graphics and CAD - Phase 4: Full Lesson Content, Part VI (continued), L33-L35

Continues 18-part6-lessons.md. Holds L33 (design for assembly and recognizing bad geometry), L34 (reviewing a model and drawing as an engineer), and L35 (the final integrated project). L34 integrates L17, L23, L28, and L33. L35 is the capstone; its full brief, options, and rubric are in Phase 5. No em dashes.