3.3 Dimensions & Fully Defined Sketches

3.3 Dimensions & Fully Defined Sketches

Quick Answer: Use Smart Dimension to add driving dimensions that match the CSWA drawing. Combine them with geometric relations until the sketch is Fully Defined (black). Never leave critical profiles blue before extruding. Driven (reference) dimensions are for measurement only. When the exam changes a key size, edit the driving dimension—relations should keep the rest of the design intent intact.

Part-modeling questions on CSWA are parametric puzzles. The first image gives a base design; a later instruction changes thickness, hole diameter, fillet size, or a sketch length. Your numeric answer (mass, volume, or center of mass) is graded after those edits. Fully defined sketches are how you ensure the solid still means what the drawing meant after the change.

Smart Dimension essentials

Smart Dimension (default shortcut often D depending on mapping) creates the appropriate dimension type from your selections:

Exam alignment tips:

• Prefer diameter dimensions for full circles when the sheet shows Ø.
• Prefer radius when the sheet shows R on a fillet-like arc in the sketch.
• Dimension to the same datums the drawing uses (origin edges, centerlines, overall sizes) so modification text maps to one obvious dimension.
• Keep units consistent with the document (MMGS is common). Do not mix interpretation of “20” as inches if the template is millimeters.

Place dimensions where they remain readable, but placement does not affect math—only the value and what it references matter for the solid.

Driving vs driven dimensions

You mark a dimension as driven when you need to see a distance that is already controlled by other dimensions/relations. Driven dimensions appear with a different style (often gray or in parentheses depending on settings) and cannot be the only tool you rely on to lock a free blue entity. If a sketch stays under-defined, you still need driving dimensions or relations—not more reference dimensions.

On the exam, almost every dimension you add from the drawing should be driving. Use driven dimensions sparingly to verify that a chain of relations produced the expected overall width before you extrude.

Fully defined, under-defined, over-defined

Fully defined (black)

Every sketch entity’s position and size is locked relative to the sketch origin and fixed references. Status bar: Fully Defined. This is the exit criterion for CSWA base and cut sketches in nearly all cases.

Benefits under modification:

• Changing a driving dimension yields a predictable rebuild.
• Features that consume the sketch (extrudes, revolves, cuts) update without silent drift.
• Mass properties reflect the intended parametric change only.

Under-defined (blue)

Something can still drag. Common missing pieces:

• Circle center free in X or Y
• Line angle free (not horizontal/vertical/parallel/angular dim)
• Endpoint gap without coincident
• Symmetric half missing a relation to the centerline

You can extrude under-defined sketches; SOLIDWORKS will not always stop you. That is dangerous on CSWA: a later edit to an unrelated feature or a rebuild can nudge free DOF, or your mental model of the size may not match what remained free. Treat under-defined as unfinished work.

Over-defined (conflicts, yellow/red)

Too many constraints fight. Examples:

• Two different width dimensions controlling the same pair of vertical lines
• Equal relation plus two unequal driving lengths on the same pair
• Horizontal relation plus a non-zero angle dimension on the same line

Resolve by deleting or converting one redundant dimension (sometimes to driven) or removing a relation. Do not suppress errors and proceed to mass properties—the geometry may not match either dimension you think is active.

Strategy: fully define before extrude

Adopt this sequence for every CSWA sketch feature:

1. Entities — correct tools for the profile (Section 3.1).
2. Relations — structure and symmetry (Section 3.2).
3. Smart Dimensions — driving values from the sheet.
4. Status check — Fully Defined / black.
5. Feature — Extruded Boss/Base, Extruded Cut, Revolve, etc.
6. Modification — edit the named driving parameter; rebuild; recompute mass.

Skipping step 4 to save thirty seconds often costs minutes of debugging when a modification fails or mass is mysteriously wrong.

Dimension schemes that survive modifications

CSWA modification language often sounds like:

• “Change the overall length from 100 mm to 120 mm.”
• “Change the hole diameter to 10 mm.”
• “Change the base extrusion depth to 15 mm.” (feature dimension, not sketch—but same idea)

Sketch for editability:

• One clear overall driving dimension for lengths that will change, plus relations that hold the internal pattern (midpoint holes, equal spacing via relations or pattern features later).
• Avoid stacking many chain dimensions that all must be hand-edited when only the overall changes—unless the drawing’s design intent is truly a chain.
• Link repeated sizes with Equal rather than duplicate driving dimensions with the same number.
• For symmetric parts, dimension overall width (or one side) + Symmetric relations rather than left and right independently.

When both a sketch dimension and a feature dimension could express thickness, follow the drawing: thin sheet thickness is often the extrude depth; plan-view sizes stay in the sketch. Mixing them without a plan causes confusion when the problem says “change thickness.”

Connecting dimensions to mass answers

Numeric entry questions expect precision (often two decimal places in MMGS with a stated material). Wrong sketch definition creates wrong volume even if you pick the correct material. Checklist before answering mass:

• Sketch black / fully defined at each critical profile
• Correct diameter vs radius interpretation
• Modifications applied to the driving dimension or feature parameter named in the problem
• Rebuild successful, no dangling errors in FeatureManager
• Material applied (density) as specified—dimensions alone do not set mass without material

Common dimensioning mistakes on CSWA-style parts

Worked intent example (mental model)

A plate 80 × 50 mm has a central Ø12 hole. Relations: center rectangle or symmetric sides about origin; hole center coincident to origin; circle diameter driving 12. Fully defined with width 80, height 50, Ø12. Extrude depth 10 mm as a feature dimension. Modification: width → 90 mm, hole → Ø14. You edit two driving values; hole stays centered; mass updates. If the hole center were only “eyeballed” without coincident to origin, the 90 mm width change might leave the hole off-center and center-of-mass questions would fail even if volume were close.

Rapid audit before you leave a sketch

1. Status bar says Fully Defined.
2. No blue segments on the contour you will extrude.
3. All drawing-critical sizes exist as driving dimensions (or equal-linked to one).
4. No conflict balloons in the PropertyManager.
5. Origin and centerlines play the role the drawing implies.

Dimensions finish the story that entities and relations start. On CSWA, that story must be fully told—in black—before you build solid features and chase mass properties under the clock.