3.1 Sketch Entities
Key Takeaways
- CSWA part models start with 2D sketches; the entity you pick (line, arc, circle, slot, rectangle) should match how the exam drawing is dimensioned so design intent survives later edits.
- Centerlines are construction geometry for symmetry, revolve axes, and midplanes—they do not create solid edges by themselves.
- Corner vs center rectangles and perimeter vs centerpoint arcs change how dimensions and relations attach; match the construction method to the given origin or center marks on the drawing.
- Slots, polygons, and ellipses appear when the exam wants a single closed profile with built-in equal/parallel intent rather than many separate lines and arcs.
- Sketch points locate holes, pierce references, and pattern centers; they are often under-defined until coincident or dimensioned to geometry.
3.1 Sketch Entities
Quick Answer: On CSWA part questions, nearly every solid starts as a closed 2D sketch. Choose the entity that matches the drawing’s geometry and dimension scheme—lines and arcs for polygonal profiles, circles for holes and bosses, slots for elongated openings, centerlines for symmetry and revolves—so relations and Smart Dimensions can fully define the sketch before you extrude.
Sketch entities are the building blocks of every SOLIDWORKS part you will build on the Certified SOLIDWORKS Associate (CSWA) exam. Basic and intermediate part questions almost always open with a multi-view drawing that implies a profile on Front, Top, or Right. Your first job is not to guess the extrusion depth—it is to recreate that profile accurately with the right entities so the model can accept later dimension changes without breaking.
Why entity choice matters on the exam
CSWA questions are scored on final mass, volume, or center of mass after one or more modifications. If you rebuild a rectangle from four loose lines without equal or parallel relations, changing one width later may leave the opposite side free and your mass wrong. Using a Corner Rectangle or Center Rectangle embeds parallel and equal intent immediately. Matching entity type to the drawing is a design-intent skill, not decoration.
Work on a standard plane (usually Front for elevation views) unless the problem states otherwise. Confirm document units (often MMGS) before dimensioning. Exit sketch only when the profile is closed (for bosses/bases) and fully defined—black geometry—unless the problem explicitly leaves a free parameter you will drive later (rare on CSWA).
Lines and centerlines
Line is the default edge for prismatic shapes: plates, brackets, L-sections, and cutouts with straight sides. Click-drag or click-click to place endpoints. Endpoints that meet other geometry need a coincident relation (often auto-added). For long runs of horizontal and vertical edges, toggle Horizontal / Vertical relations rather than approximating angles with freehand lines—exam drawings almost always align with the origin axes.
Centerline (construction line) does not produce a solid edge when you extrude. Use it for:
- The axis of a Revolve Boss/Base or Revolve Cut
- A mirror line before Mirror Entities
- A midplane construction for Symmetric relations
- Construction only when you need reference direction without adding mass
On drawings, a dashed center mark or symmetry line is your cue: sketch a centerline, then relate solid geometry to it. Forgetting to set a revolve axis as a centerline (or selecting the wrong axis) is a common mass error on revolve-style CSWA parts.
Rectangles: corner vs center
| Tool | How it places | Best exam cue |
|---|---|---|
| Corner Rectangle | Two opposite corners | Drawing gives overall width/height from a corner or datum edge |
| Center Rectangle | Center point then corner | Drawing shows a part centered on origin or midplanes; mods keep symmetry about center |
| 3 Point Corner / 3 Point Center | Angled rectangles | Skewed plates; less common on standard CSWA base sketches |
Corner rectangles auto-create four lines with horizontal/vertical and equal opposite sides when you stay orthographic. Center rectangles pin the sketch center—ideal when the problem origin is the part center and later modifications change outer size but keep the center fixed. If the exam later “increases width by 10 mm,” a center rectangle with a single width dimension and symmetry often updates cleaner than four independent side dimensions.
Circles and arcs
Circle (center-radius) is the standard for holes, bosses, pins, and cylindrical cuts. Place the center with a point relation to origin, midpoints, or construction geometry, then Smart Dimension the diameter (CSWA drawings usually give diameter, not radius). Prefer diameter dimensions to match the drawing callouts so modification instructions (“change Ø20 to Ø22”) map one-to-one.
Arcs appear on filleted profiles in the sketch (as opposed to Fillet features after extrude) and on open profiles for thin features or revolves:
| Arc type | Construction | Exam use |
|---|---|---|
| Centerpoint Arc | Center, start, end | Radii called out from a clear center (pulleys, sectors) |
| Tangent Arc | Continues from existing endpoint tangent to prior entity | Smooth transitions already implied between line and arc |
| 3 Point Arc | Three points on the curve | Arc through three known points; less common when radius is given |
| Perimeter (3-point style) variants | Defined by perimeter points | When the drawing dimension scheme does not expose the center |
If the drawing shows a radius bubble to an arc and the center is obvious from concentric circles, use Centerpoint Arc and a concentric relation to the related circle. If only chord endpoints and a radius are given, a centerpoint arc plus radius dimension, or a 3-point arc constrained to endpoints, both work—pick the method that leaves the fewest free degrees of freedom.
Slots, ellipses, and polygons
Straight Slot and Centerpoint Straight Slot create two parallel sides and two semicircles as one closed profile. Exam drawings with elongated holes for adjustment often expect a slot rather than two arcs and two lines you must manually equalize. Dimension length (overall or center-to-center, matching the drawing) and width. Centerpoint Arc Slot / 3 Point Arc Slot appear when the slot follows a curved path—rarer on basic CSWA but possible on intermediate profiles.
Ellipse builds oval bosses or cuts when the drawing shows major and minor axes. Dimension both axes; do not approximate an ellipse with many arcs unless the problem truly shows multi-radius geometry.
Polygon (n-sided) is efficient for hex flats, nut-shaped bosses, or regular cutouts. Set side count, inscribed or circumscribed circle mode to match whether the drawing dimensions across flats or across corners, then constrain the circle diameter and orientation (often a horizontal/vertical side or a vertex on an axis).
Points and entity selection strategy
Point entities mark centers for future holes, pierce locations for 3D curves/planes, or endpoints you want to dimension without adding a visible edge. A lone point stays blue until it is coincident to intersection geometry or fully dimensioned in both directions.
Exam selection strategy:
- Identify closed outer profile vs internal islands (holes).
- Prefer native tools (rectangle, slot, polygon, circle) over many free lines when the shape matches.
- Use centerlines for symmetry and revolve axes before solid entities when the drawing shows them.
- Place construction geometry first if the drawing is origin-centered; then snap solid entities with relations.
- Fully define with relations + Smart Dimensions before Extruded Boss/Base or Extruded Cut.
Typical CSWA drawing cues → entity
| Drawing cue | Likely entity |
|---|---|
| Rectangular plate with corner radii later as features | Corner or center rectangle; fillets as features, not sketch arcs (unless shown as 2D profile radii) |
| Through hole with Ø callout | Circle, diameter dimension |
| Elongated mounting hole | Straight slot |
| Symmetric part about vertical centerline | Centerline + symmetric relations or center rectangle |
| Hexagonal boss | Polygon, 6 sides |
| Revolved handle or pulley half-profile | Lines + arcs + centerline axis |
| Hole centers on a bolt circle | Points or circle centers with equal spacing / circular pattern later |
Workflow checklist before leaving the sketch
- Profile closed where a solid boss requires a closed contour; select correct contour if multiple regions exist.
- No unintended tiny gaps at corners (zoom endpoints; add coincident).
- Construction geometry marked as construction where it should not create edges.
- Dimensions match the sheet’s scheme (overall vs chain vs baseline) enough to allow the stated modifications.
- Status: Fully Defined in the window corner; geometry black, not blue.
Mastering entities reduces mouse time under the 3-hour CSWA clock and, more importantly, produces models that absorb the exam’s “now change this dimension” step without rebuild failures or wrong mass properties.
On a CSWA drawing, a rectangular base is centered on the origin and later modifications keep the part symmetric while changing overall width. Which sketch tool best supports that design intent?
What is the primary modeling role of a centerline in a sketch that will become a revolve feature?
An exam drawing shows an elongated mounting hole with parallel sides and semicircular ends, dimensioned by overall length and width. Which entity is the most efficient choice?
Why should you prefer a native circle with a diameter Smart Dimension for a through-hole shown as Ø18 on a CSWA sheet?