11.1 Reference Planes

11.1 Reference Planes

Quick Answer: Insert → Reference Geometry → Plane builds construction planes when you cannot sketch on Front, Top, Right, or a model face. CSWA most often needs an Offset Plane (parallel to a face/plane at a given distance), then Mid Plane, At Angle, and through points/lines constructions. Create the plane first, start a sketch on it, fully define the profile, then extrude or cut—wrong plane distance or parent destroys mass even if sketch dimensions match the sheet.

Default planes and planar faces cover basic parts. Intermediate and advanced CSWA models frequently place a boss, pocket, or hole sketch away from existing faces: a plate with a raised pad starting 15 mm above the base, a feature on the midplane between two walls, or a rib sketched on a plane rotated 30° about an edge. Official prep paths list Planes under reference geometry, and Part-style checklists explicitly call out creating the correct offset plane. Treat planes as first-class exam tools—not optional CAD niceties.

Why reference planes matter for CSWA mass

Mass Properties measure the finished solid. If a sketch is on a plane 10 mm too high, an extrude of the correct depth still sits in the wrong place, volume shifts, and CoM moves. The sketch may be fully defined and green; the plane was the error. Always verify:

1. Parent geometry (which face or plane you offset from)
2. Offset distance and direction (flip if the plane is on the wrong side)
3. That the new plane is selected when you start the sketch (FeatureManager highlight / sketch plane name)

Creating a reference plane (workflow)

1. Insert → Reference Geometry → Plane (or Features tab → Reference Geometry → Plane).
2. In the Plane PropertyManager, select references in the order the message bar expects (first face/plane, then point or second face, etc.).
3. Choose or confirm the constraint type SOLIDWORKS infers: Offset Distance, Parallel, Perpendicular, At Angle, Mid Plane, Coincident, etc.
4. Enter distance or angle when required; use Flip offset if the preview is on the wrong side of the parent.
5. Preview the translucent plane; rename it in the FeatureManager (recommended for multi-plane models).
6. OK, then Sketch on that plane (right-click plane → Sketch, or select plane then Sketch).

You can also create planes from the Reference Geometry flyout while editing features—keep the tree clean so parent-child links stay readable when you roll back.

Offset Plane (highest yield)

Offset Plane is the CSWA workhorse. Select a planar face or default plane as Reference 1, set Offset distance, and flip if needed. The new plane is parallel to the parent at that separation.

Typical exam callouts:

• "Boss begins 20 mm above the top face of the base" → Offset 20 mm from top face; sketch boss profile; extrude upward (or Blind in the correct direction).
• "Cut sketch is on a plane 12 mm from Front" → Offset Front by 12 mm; sketch cut; Extruded Cut.
• "Hole pattern on a plane parallel to Right at 40 mm" → Offset Right 40 mm; sketch and cut or Hole Wizard on that plane.

Signed distance discipline: Drawings often dimension from a face to the start of a feature. If you offset the wrong face (bottom instead of top) or forget Flip, the plane may still show a number that "matches" the sheet while the solid is mirrored relative to the part. After creating the plane, rotate the model and check that the plane sits on the side the orthographic views imply.

Offset from default plane vs face: Offsetting Top is stable when the base thickness may change later; offsetting the top face of the base extrude tracks that face if the base height is edited. Prefer the parent that matches design intent on the exam sheet (usually the face called out by the dimension).

Parallel at a point (related pattern)

A common PropertyManager pattern is parallel to a plane/face and coincident with a point (or through a vertex). You pick the planar reference and a point/vertex; SOLIDWORKS builds a plane parallel to the first reference that passes through the point. Use this when the drawing gives a parallel orientation plus a locating point rather than a pure distance—or when the point already defines the height (intersection of edges, sketch point, reference point).

Mid Plane between faces

Select two parallel planar faces (or two parallel planes). SOLIDWORKS places a plane halfway between them. Ideal for:

• Symmetric cuts or slots through the thickness without calculating half-thickness offsets
• Ribs or webs centered in a cavity
• Features that must stay centered if wall spacing changes (exam intent: midplane symmetry)

If faces are not parallel, Mid Plane is not available—use another construction (angle or through entities).

At Angle plane

Select a linear edge or axis as the axis of rotation and a planar face or plane as the angular reference (or follow the on-screen reference order). Enter the angle and flip if the rotation sense is wrong.

CSWA use cases:

• Angled boss or tab sketched on a plane rotated from a side face
• Chamfer-like extruded shapes that are truly sketched on an angled plane rather than using Chamfer feature
• Draft-related geometry that the sheet defines by sketch angle about an edge

After the plane exists, sketch the profile in that plane’s 2D space. Do not try to force an angled extrude direction alone to replace a required angled sketch plane when the profile itself must lie at an angle.

Through entities: 3 points, line + point, two lines

These constructions appear less often than Offset on basic parts but show up when geometry is defined by vertices rather than a face offset. If the three points become collinear after an edit, the plane fails—prefer robust parents when the sheet allows.

When the drawing needs a sketch on an offset plane

Read the sheet for distance from a face to a sketch plane or feature start plane that is not an existing solid face:

1. Identify the parent face/plane and the dimension value.
2. Create Offset Plane with that distance; Flip to match view orientation.
3. Sketch on the new plane; apply dimensions relative to projected edges or convert entities as needed.
4. Extrude with Blind/Through All/Up to Surface as the drawing specifies—do not double-count the offset as extrude depth.

Trap: Using Up to Surface or a deep Blind extrude from the base face to "reach" a height without creating the offset plane can work for simple bosses but fails when the sketch itself must live at that height (different profile than the base, local hole pattern, or partial contour). If the drawing shows a profile drawn on a plane parallel to the face at distance d, build the plane.

Sketching and feature direction on reference planes

• Normal direction: Extrude arrows point along the plane normal; reverse direction if material goes the wrong way.
• Convert Entities / Offset Entities: Project edges from other features onto the new plane for alignment with below geometry.
• Fully define sketches on reference planes the same as on default planes—under-defined sketches still break design intent.
• Hide planes after use (right-click → Hide) to declutter; they remain in the tree for edits.

Exam scenario: angled extrude plane

Drawing: side view shows a rectangular boss whose sketch plane is 30° from the vertical face, rotating about the top front edge of the base. Workflow:

1. Select the top front edge as the axis reference and the front (or vertical) face as the planar reference.
2. Plane → At Angle → 30° → confirm preview matches the side view (flip angle if mirrored).
3. Sketch rectangle on the angled plane; dimension width/height per sheet.
4. Extrude Blind to the depth normal to that plane (or as specified).
5. Apply material and Mass Properties—compare to the expected mass band.

If you instead extrude from the vertical face with a 30° draft, you get different geometry than a true angled sketch plane. Match the construction the views describe.

Checklist before continuing features

Link to patterns, holes, and later chapters

Offset and mid planes often host Hole Wizard or seed holes for Circular/Linear Pattern. Axes for circular patterns are covered in §11.2; the plane only positions the seed. Advanced multi-feature parts (Ch9) stack several reference planes—rename them and keep FeatureManager order clear for rollback edits.

Master Offset Plane until it is automatic; then add Mid Plane and At Angle until previews match orthographic intent every time.