8.2 Circular Pattern

8.2 Circular Pattern

Quick Answer: Insert → Pattern/Mirror → Circular Pattern copies a seed feature around an axis (temporary axis, reference axis, or linear edge). Set number of instances (includes seed) and either Equal Spacing over an angle (often 360°) or a fixed angular spacing. Intermediate CSWA parts use this constantly for bolt circles and radial bosses.

If Linear Pattern is the tool for grids, Circular Pattern is the tool for anything that repeats around a center—flange bolt holes, cooling holes on a hub, radial ribs, or bosses on a pulley. Official CSWA category language places circular pattern techniques in Intermediate Part Creation and Modification. Treat this section as high-yield: intermediate items are 15 points each, and a wrong axis or instance count fails mass just as hard as a wrong extrude depth.

What Circular Pattern builds

The feature takes one or more seed features and creates additional instances rotated about a common axis of revolution. Each instance inherits the seed’s shape while revolving its position around that axis. The result is associative: change the seed diameter or the pattern count, and all instances update together.

Axis of revolution — the critical selection

Without a correct axis, the pattern orbits the wrong center. Mass, CoM, and hole positions all fail.

Acceptable axis selections (CSWA-relevant)

1. Temporary axis of a cylindrical or conical face

   • Show temporary axes (View → Hide/Show → Temporary Axes or the Heads-up visibility controls, depending on version).
   • Click the axis that runs through the true center of the hub/boss cylinder that defines the bolt circle.

2. Model edge that is linear and coincident with the design centerline

   • Example: a vertical edge on a rectangular center rib that lies on the axis of symmetry (less common than temp axes for round hubs).

3. Reference Axis feature (Insert → Reference Geometry → Axis)

   • Define from cylindrical face, two planes, edge + vertex, etc.
   • Useful when temporary axes are cluttered or the center is defined by intersecting planes.

4. Sketch centerline / axis-capable line in some workflows when exposed as a selectable axis reference

   • Many users create a reference axis from the sketch or from Front/Right plane intersection for clarity.

Exam trap — patterning about a seed hole’s own axis: If you select the temporary axis of the seed hole instead of the hub, instances spin about the hole center (nearly on top of each other or in a tiny orbit). Always select the center axis of the circular layout, not the axis of the feature being copied.

Exam trap — offset axis: An axis parallel to the true center but offset by a few millimeters produces a wrong bolt-circle diameter. Preview in a view looking along the axis; instances should land on the drawn circle.

Equal Spacing vs angle increment

Equal Spacing (most common for full bolt circles)

Enable Equal Spacing and set the total angle (usually 360°) plus Number of Instances. SOLIDWORKS divides the angle into equal steps.

Formula intuition: For full circle Equal Spacing, angular step ≈ 360° / N between adjacent instances (seed included in N).

Examples:

Fixed angular spacing (Equal spacing off)

You specify the angle between instances and the count. Three instances at 30° spacing occupy a 60° sector from first to last step pattern logic—read the PropertyManager preview carefully so you do not double-count.

Full 360° vs partial patterns

Partial pattern trap: Leaving 360° Equal Spacing when the drawing only shows three holes on a quarter flange creates extra holes through solid regions that should remain blank—mass drops too far. Match the visible count and arc.

Instance count includes the seed (again)

Same rule as Linear Pattern:

• N = total features after the pattern completes, including the original seed.
• Six bosses on a hub → Instances = 6, not 5.

Worked example: Seed cut at the top of a flange. Drawing: 6× Ø10 equally spaced on a bolt circle. Circular Pattern → axis through flange center → Equal Spacing → 360° → Instances 6. Preview should show six holes at 60° increments.

If you accidentally set Instances = 5, one hole is missing; mass is too high (for holes) and the visual no longer matches.

Seed feature choice

What to select

• The Extruded Cut, Hole Wizard, Extruded Boss, or other feature that defines one radial unit.
• Related local features that must repeat with each unit (for example, a counterbore feature stack, or a small fillet only on that boss)—multi-select features to pattern.

What not to do

• Do not pattern the entire base revolve that creates the hub unless the drawing wants multiple hubs.
• Do not leave the seed under-defined; every copy inherits dimensional mistakes.
• Do not create six separate Hole Wizard positions manually when one seed + circular pattern is enough—edits become painful.

Hole Wizard + Circular Pattern: Common robust workflow: place one Hole Wizard hole at the correct bolt-circle radius and angular position, then Circular Pattern that Hole Wizard feature about the center axis. Alternative: sketch multiple points in Hole Wizard’s placement sketch—also valid, but pattern-of-feature is often cleaner when the exam later changes count.

Seed position on the bolt circle

Position the seed at the correct radius (distance from axis to hole center) and at a starting angle that matches the drawing (for example, first hole on the vertical centerline). Patterning only rotates copies; it does not fix a seed that sits at the wrong radius. Wrong radius → wrong material removal locations → wrong mass and CoM.

Features vs bodies in circular patterns

For standard CSWA flanges, use Features. Body patterns appear when a multi-body design intentionally repeats separate solids around an axis.

Geometry Pattern and other options

As with linear patterns, Geometry Pattern may be available. Prefer the default feature pattern for exam stability when seeds use face-referencing end conditions. Use Instances to Skip if a drawing omits one position on an otherwise equal pattern (for example, five holes on a six-position bolt circle with one station empty).

Vary sketch and instance-by-instance modifiers exist in professional workflows; associate-level drawings almost always want constant identical copies.

Circular vs Linear decision table

Intermediate part scenarios (exam style)

Scenario A — Flange with bolt circle: Revolve or extrude the flange body → seed hole at correct PCD → Circular Pattern 6× about temp axis → fillets → material → Mass Properties. Modification: change to 8× equally spaced; edit instance count only; re-measure.

Scenario B — Hub with radial bosses: Extrude one boss at radius R → Circular Pattern 4× → optional circular pattern of cuts on bosses → mass. Wrong axis through a boss instead of hub center is the failure mode.

Scenario C — Partial pattern on a sector bracket: Only three holes along a 120° arc. Set angle and instances to match; do not force 360°.

Modification and mass discipline

1. Edit CirPattern feature (count, equal spacing angle, or axis if rebuild requires).
2. Rebuild; confirm no unwanted cuts through critical walls.
3. Material still present; units still MMGS (or as specified).
4. Mass Properties / CoM as required—radial hole count changes mass significantly on steel parts.

CoM note: Symmetric full-circle patterns about the origin often keep CoM near the axis; partial patterns or skipped instances shift CoM. If the exam asks for center of mass coordinates, re-measure after every pattern edit.

Circular Pattern checklist

1. Build body; locate true center axis (temp axis or reference axis).
2. Create one correct seed at proper radius and start angle.
3. Circular Pattern → select seed feature(s) → select hub axis (not seed hole axis).
4. Equal Spacing + 360° for full circles; set N including seed.
5. Preview along-axis view; compare to drawing count and PCD.
6. Skip instances only if the sheet shows gaps.
7. Modify via Edit Feature; always re-run Mass Properties.

Mastering Circular Pattern is non-negotiable for intermediate CSWA credit. Axis discipline, seed radius, and instance count (including seed) are the three checks that separate a clean 15-point model from a near-miss mass entry.