Stage 3: Parametric Design

Goal#

After this stage you can build a model whose size and features are controlled by a short, well-named parameter table, change those parameters without breaking the timeline, and produce several sizes of a product from one file.

This matters for product design because a real product is never one size. A handheld enclosure has to fit a 60 mm board today and an 80 mm board next month, the client will ask for a thicker wall after the first print, and a marketing request will add a fourth colour or a variant with no display cutout. A model built from constants has to be redrawn each time. A model built from parameters changes in minutes and, just as important, shows you its own limits: you learn which parameter values are safe before a customer finds out.

Before you start#

• Stage 1 and Stage 2 (or equivalent): you can sketch with dimensions and constraints, and extrude, revolve, shell, fillet, chamfer and pattern.
• You can save a design, name bodies, and use Measure to read a dimension.
• You are comfortable with the Browser and know where Modify > Change Parameters lives.
• Licence note for this path: everything marked required works on a standard Fusion licence. The Configuration Table is described in Autodesk's help without a licence statement, but Personal-use entitlement is not confirmed there, so every configuration task below has a no-configuration route as well. Configuration Rules belong to the Design Extension and appear only under "Optional (extension required)".

Learn#

Work through these in order. Each page has a practice exercise at the end; you will do them in the next section.

• Read Parametric vs. Direct Modeling - decide which mode you are in before you build; this stage assumes Parametric mode with history captured.
• Read The Timeline - the timeline is the model; learn to read, rename, group and suppress entries. Focus on "Reading dependencies" and "Suppress as a diagnostic".
• Read Rollback and Editing Features - how to edit an early feature or insert a new one mid-timeline safely.
• Read Units and Expressions - unit mismatches are the most common cause of "why is my equation red".
• Read The Change Parameters Dialog - the control panel for everything below. Focus on the Options reference and the CSV export and import section.
• Read User Parameters and Equations - the core skill of the stage. Read "Designing the parameter set" twice.
• Read Design-for-Change Patterns - ten habits that decide whether a model survives a 40 percent size change. Focus on the Stress-test protocol.
• Read Timeline Errors - you will break your own model on purpose in the drills; learn the repair routine first.
• Read Configurations - how a configuration table turns one model into a family. Skim the Options reference; read "Choosing between configurations, parameters and separate files" closely.
• Read Best-Practice Modeling Workflows - the start-to-finish routine you will follow in the checkpoint project.

Practice#

Do the page exercises first, then the drills.

• Do the practice exercise on The Timeline
• Do the practice exercise on Rollback and Editing Features
• Do the practice exercise on The Change Parameters Dialog
• Do the practice exercise on User Parameters and Equations
• Do the practice exercise on Design-for-Change Patterns
• Do the practice exercise on Timeline Errors
• Do the practice exercise on Configurations (or, without configurations, make three Save As copies of the model with different parameter values)

Drills (10 to 20 minutes each):

• Drill 1, expression fluency. In a new design, create user parameters a = 40 mm, b = a * 1.5, c = b - 2 * 3 mm and n = 5 (No Unit). Read the Value column: b should be 60 mm and c 54 mm. Now try to create d = a + n. Read the error, then fix it so d is a length (a + n * 1 mm) giving 45 mm. Write one sentence on why the first attempt failed.
• Drill 2, one number drives everything. Sketch a rectangle from the origin, dimension it with box_l and box_w, extrude to box_h, and shell with wall. Set box_l = 80 mm, box_w = 50 mm, box_h = 30 mm, wall = 2 mm. Measure the inner cavity length: it should read 76 mm. Change wall to 3 mm and confirm the cavity becomes 74 mm without touching a sketch.
• Drill 3, break and repair. Make a block with a sketch on its top face, a hole referenced to that face, and a fillet on one edge. Delete the original extrude's profile reference by editing the first sketch so that the face changes shape, find the first red marker, and repair it without deleting later features. Record the name of the failing feature and the fix.
• Drill 4, stress test. Take the model from Drill 2 and set box_l to 50 percent, 150 percent and 200 percent of nominal one at a time (40, 120 and 160 mm). Record any timeline error. Then set wall to 14 mm and record what fails first and why. Add the safe range to the parameter comment.

Checkpoint project#

Project: a parametric enclosure family. Time estimate: 3 to 4 hours.

Design one printable project-box enclosure (a base and a lid) around a circuit board, driven entirely by parameters, then produce three sizes from the same file. This is the first piece of the capstone consumer product: you will reuse the parameter table in later stages.

The box is built as two bodies in one design (components come in Stage 4). If you later want a snap-fit lid, Tutorial 2: Electronics Enclosure with Snap-Fit Lid is a good follow-up after Stage 4; it uses the same parametric thinking.

Parameter table (create these first, before drawing anything):

Build order: sketch the outer rectangle with box_l and box_w, extrude to box_h, then cut the cavity using wall-based offsets (or shell, if you leave the top open). Add four standoffs at the board mounting-hole positions (spacing pcb_l - 2 * hole_inset by pcb_w - 2 * hole_inset, which is 52 mm by 32 mm for the small size), each boss_od across with a pilot_d hole. Add one rectangular connector cut-out on a short wall. Make the lid a separate body whose outline follows box_l and box_w.

Follow the design-for-change habits: anchor sketches to the origin, fully constrain them, reference planes and construction geometry rather than faces you created later, name every feature, and group the timeline into "Base", "Standoffs", "Cut-outs" and "Lid".

Three sizes:

Create the three sizes with a configuration table (rows Small, Medium, Large; parameter columns pcb_l and pcb_w) if your licence has it, otherwise make three Save As copies and change the two inputs in each.

Deliverables

• A parameter table with at most 13 parameters, all named in lowercase with underscores, each input commented with its meaning and units
• A base and a lid that both rebuild without any red marker at all three sizes
• Standoffs that land 4 mm in from each board corner at every size (check the Medium spacing reads 72 mm by 42 mm)
• A timeline with no unnamed sketches or features, grouped as listed above
• A short limits note in the parameter comments: smallest and largest pcb_l you tested
• Three sizes saved (configurations, or three files)

Challenges#

These are briefs, not tutorials. Use the Learn pages to find your own route.

Challenge 1: Adjustable phone stand#

Brief: A client sells a desk phone stand and wants one model that fits a phone, a slim case and a small tablet by changing one number.

Constraints: FDM print, PLA, wall and plate thickness 4 mm. Base plate 90 mm wide by 70 mm deep. The slot width equals phone thickness plus 2 x 0.5 mm clearance; nominal phone thickness 9 mm. Backrest tilt between 60 and 75 degrees from the base, nominal 70. Front lip 15 mm high.

Deliverables

• User parameters phone_t, slot_clr, tilt, base_w, base_d, plate_t, lip_h
• A derived parameter slot_w computed from the inputs
• A model that prints flat on its base with no support under the slot

Self-check

• Measure the slot width: it reads 10.0 mm at nominal
• Set phone_t to 12 mm: the slot reads 13.0 mm and the model rebuilds with no error
• Set tilt to 60 and then 75: the backrest angle changes and the lip height stays 15 mm
• Change plate_t to 5 mm: every plate section thickens and no feature fails

Stretch: Make the stand rebuild correctly for phone_t up to 20 mm, and state the largest tilt at which the phone no longer tips backwards.

Hint: see Design-for-Change Patterns (anchor to origin, parameters for intent).

Challenge 2: Desk pen organizer with a safe pen count#

Brief: A stationery brand wants a solid desk organizer with a ring of round pen holes, and a promise that any hole count up to some limit still works.

Constraints: Cylinder 80 mm in diameter, 40 mm high. Pen holes 12 mm in diameter, 30 mm deep, centres on a 56 mm pitch circle (28 mm radius). Minimum web between neighbouring holes 3 mm. Hole count n_pens between 3 and 11.

Deliverables

• A circular pattern whose quantity is driven by n_pens
• A check parameter (for example web) that shows the web between holes: the chord 2 * r * sin(180 deg / n_pens) minus the hole diameter
• A limits note in the comments

Self-check

• At n_pens = 6 the web reads 16 mm; at 8 it reads about 9.4 mm
• At n_pens = 11 the web reads about 3.8 mm and the model rebuilds
• At n_pens = 12 your check parameter reads about 2.5 mm, below the 3 mm rule, so your limits note names 11 as the maximum
• The outer rim beyond the holes stays at least 6 mm at every count (40 mm radius minus 28 mm minus 6 mm hole radius)

Stretch: Cap the pitch-circle radius automatically with min() so the rim is never thinner than 6 mm if someone enlarges the hole diameter.

Hint: see Units and Expressions for functions, and the Stress-test protocol in Design-for-Change Patterns.

Challenge 3: Battery tray that grows with the cell count#

Brief: A hobby-electronics client needs a tray for 2, 3 or 4 AA cells side by side, and wants a fifth variant later without a redraw.

Constraints: AA cell 14.5 mm in diameter by 50.5 mm long (typical). Pocket diameter equals cell diameter plus 0.8 mm (0.4 mm clearance per side), so 15.3 mm. Pocket length across the tray equals cell length plus 0.8 mm. Wall between and around pockets 2 mm. Pocket depth 9 mm, floor 2 mm.

Deliverables

• Parameters n_cells, cell_d, cell_l, clr, wall
• Tray length and width as equations, not typed numbers
• A pocket pattern driven by n_cells

Self-check

• Tray length is n_cells * 15.3 + (n_cells + 1) * 2 mm: 36.6 mm for 2 cells, 53.9 mm for 3, 71.2 mm for 4
• Tray width reads 55.3 mm (51.3 plus 2 x 2)
• Changing n_cells from 2 to 4 leaves no red marker and no overlapping pockets
• Changing clr to 0.6 mm per side widens pockets to 15.7 mm and the tray grows to match

Stretch: Add a thumb notch whose size follows cell_d.

Hint: see User Parameters and Equations, "Drive counts and angles".

Challenge 4: Rescue a fragile model#

Brief: An intern built a bracket by clicking faces for every reference. A late request changes the base size and the model collapses. Reproduce that failure and rebuild it to be robust.

Constraints: Bracket base 50 mm by 30 mm by 5 mm with an upright 5 mm thick and 30 mm high, two 5 mm holes 8 mm in from the base ends, 3 mm fillet on the upright. Build a deliberately fragile version first (holes dimensioned to the face edges, no parameters), then a robust version.

Deliverables

• The fragile version, with a note of which feature broke first when the base grew to 80 mm
• The robust version, with parameters, origin-anchored sketches and named features
• A timeline with a feature inserted mid-timeline using the marker (a 1 mm chamfer on the base edges)

Self-check

• The robust version rebuilds at base lengths of 25, 50 and 100 mm with no red marker
• At 100 mm the hole centres are still 8 mm from each end (so 84 mm apart)
• The chamfer added mid-timeline did not change the hole positions
• The Browser shows no unnamed Sketch or Extrude entries

Stretch: Add a check so a base shorter than 25 mm gives a clear failure name rather than an arbitrary one.

Hint: see Timeline Errors and Rollback and Editing Features.

Challenge 5: Parameter handoff by CSV#

Brief: A colleague will tune your enclosure from a spreadsheet and send it back.

Constraints: Use the enclosure from the checkpoint. The CSV must contain all inputs and no derived values that would be overwritten.

Deliverables

• An exported parameter CSV
• The CSV edited in a spreadsheet: wall from 2 mm to 2.4 mm and pcb_l to 70 mm
• The edited file imported back

Self-check

• After import, box_l reads 76.8 mm (70 + 2 x (1 + 2.4))
• box_w reads 46.8 mm (40 + 2 x 3.4)
• The standoff spacing along the length reads 62 mm (70 minus 2 x 4)
• No parameter lost its unit or comment

Stretch: Document in the comments which columns the colleague may change and which are derived.

Hint: see the CSV section of The Change Parameters Dialog.

Optional (extension required): Configuration Rules#

Fusion's Configuration Rules belong to the Design Extension, so this task is never required.

Brief: The Medium and Large enclosures should switch automatically from a screw-fixed lid to a larger boss pattern.

Deliverables

• A configuration table with a theme table that suppresses the extra bosses at the Small size
• A rule that selects the theme from the board size

Self-check

• Activating each configuration shows the expected bosses and no timeline errors

Hint: see Configurations, "Use a theme table".

You have finished this stage when#

• I can open Change Parameters and create an input parameter, a derived parameter and a count parameter without a unit error.
• I can drive a sketch dimension and a feature distance from a named parameter.
• I can roll back the timeline, edit an early feature and insert a new one mid-timeline without breaking later features.
• I can find the first failing feature when the timeline shows an error and repair it without rebuilding.
• I can stress-test a model at 50, 150 and 200 percent of nominal and write down its safe range.
• I can produce at least three sizes of one product from one parameter set.
• I can explain when to use parameters, configurations or separate files.

Next stage#

Continue with Stage 4: Assemblies and Mechanisms.