Construction Planes, Axes, and Points

Overview#

Construction geometry is invisible-in-manufacturing reference geometry: planes to sketch on, axes to revolve and pattern around, and points to locate things. Fusion's origin provides three planes, three axes and one point. Everything else you build from the model itself, so references stay associative: move a face and a plane built from it follows.

Good construction geometry is the difference between a model that survives edits and one that explodes when you change a dimension.

Where to find it#

• Workspace: Design.
• Tab / panel: Solid tab > Construct. The menu lists the User Coordinate System, plane, axis, and point tools.
• Shortcut: none listed in Autodesk's shortcut reference.
• Origin: In the browser, expand Origin and click the eye icon to show the default planes, axes and point.
• Visibility: Construction items are listed in the browser under Construction; toggle their lightbulbs.

Step by step#

Construction planes#

1. Construct > choose a plane tool (for example Offset Plane).
2. Select the reference (face, plane, edge, or points as the tool requires).
3. Enter the values (distance, angle).
4. OK. The plane appears in the browser and timeline.

Plane tools in the Construct menu (per Autodesk's Construction geometry help; the Construct menu also has a User Coordinate System tool for custom coordinate systems used in assembly constraints and manufacturing setups):

• Offset Plane: at a specified distance from an existing face or plane.
• Plane at Angle: at an angle relative to a linear edge or axis that lies on the plane (optional Offset).
• Tangent Plane: tangent to a cylindrical or conical face, positioned by an Angle (optional Reference Object and Offset).
• Midplane: an equal distance from two existing faces or planes.
• Plane Through Two Edges: passes through two edges or axes that lie in the same mathematical plane.
• Plane Through Three Points: defined by three vertices or points.
• Perpendicular Plane: perpendicular to a planar or curved face, or to a construction plane, with placement and sizing controls.
• Plane Along Path: perpendicular to an edge, sketch line, chain of connected edges or construction axis (the Path), placed by Extent Type: Proportional (a proportion of the path length), Absolute (a physical distance) or To Object (through a vertex, construction point or sketch point).

Construction axes#

• Axis Through Cylinder/Cone/Torus: the central axis of a round face.
• Axis Perpendicular To Face: passes through a face or plane at a chosen point, at a right angle.
• Axis Through Two Planes: the intersection line of two planes.
• Axis Through Two Points: line between two points.
• Axis Through Edge: along a straight edge.

Construction points#

• Point at Vertex.
• Point Through Two Edges: intersection of two edges, including extended intersections.
• Point Through Three Planes: where three planes meet.
• Point at Center of Circle/Sphere/Torus.
• Point at Edge and Plane: where an edge pierces a plane.
• Point Along Path: at a distance along a curve.

Worked example: a sloped mounting face#

1. Model a block. Pick the top edge of the front face.
2. Construct > Plane at Angle: select the edge so it lies on the plane, then set the angle to 15 degrees and check in the preview which way it tilts.
3. Sketch on the new plane and Extrude Cut to produce a slanted pocket.
4. Edit the angle later via the timeline and the pocket follows.

Options reference#

Tips and pitfalls#

Tip: Rename important planes in the browser. "Parting Plane" is more useful than "Plane 7" six months later.

Tip: A Midplane is the reliable way to make a symmetry plane for Mirror; it stays centered even when the part width changes.

Warning: Construction planes built from faces that are later deleted or heavily edited can lose their reference and flag red. Prefer references to origin planes or stable features for long-lived models.

Warning: Planes created in Direct Modeling mode (history off) are not parametric; they do not update.

• Hidden planes still work. Hide them to declutter the canvas; do not delete them.
• Planes have a Resize setting (Default fits the geometry, Extended fills the view); the displayed size is for display.
• You can sketch directly on a construction plane, or use it as a mirror plane, split tool, or loft section plane.
• The origin point is at the center of the design; moving the origin is generally avoided. Use Move/Copy on the body instead.
• Axes used for Circular Pattern or Revolve do not need to be visible.
• Axis Through Cylinder/Cone/Torus is the best way to get the true center of a bore for a circular pattern.

Choosing references that survive edits#

The most common reason construction geometry breaks is a reference to something that later changes identity. Rank your references from most to least stable:

1. Origin planes and axes. Never move or disappear.
2. Sketch geometry (a sketch line used as an axis or path).
3. Other construction geometry built from the origin.
4. Faces and edges created by early, simple features such as the base extrude.
5. Faces and edges created by late features such as fillets, chamfers or shells, which can be renumbered or consumed by edits upstream.

If a plane must sit "at the top of the part", build it as an Offset Plane from the origin plane with a named user parameter such as height, not from the top face. The face approach moves with the part but fails if you later add a chamfer that replaces the face.

Worked example: a symmetric hole pattern on a tapered body#

A 60 mm wide base tapers to a 40 mm top over 50 mm of height, and you need a pin hole on the sloped side wall, perpendicular to the wall.

1. Construct > Plane Through Three Points on three vertices of the sloped face. The plane lies on the wall.
2. Construct > Axis Perpendicular To Face, select that plane, then a point at the center of the wall (use Point At Vertex on a midpoint, or a sketch point).
3. Sketch a circle on the wall plane at that point, diameter 6 mm, and Extrude Cut 8 mm. The hole is exactly normal to the wall.
4. Mirror it across a Midplane between the left and right walls. If the base width changes to 70 mm both the wall plane and the midplane update, so the hole pair stays symmetric.

Plane Along Path for lofts and sweeps#

For a Loft you often need profiles at specific stations along a rail. Draw the rail, then use Construct > Plane Along Path with Extent Type Proportional: 0, 0.33, 0.66 and 1.0 give four evenly spaced planes perpendicular to the path. Sketch an ellipse of 20 x 12 mm on the first, 30 x 18 on the second, and so on. Planes are perpendicular to the path tangent, so a curved rail yields rotated sections automatically. With Absolute type and 25 mm you get absolute spacing, which does not rescale if the rail is lengthened. Choose Proportional when the design should stretch, Absolute when stations are dimensioned.

Plane at Angle numbers#

Plane at Angle creates a plane through the selected edge or axis at the angle you set. The angle is measured from a reference orientation, so a 15 degree plane might tilt 15 degrees from the top face or from vertical; if your pocket ends up at 75 degrees, the angle is measured the other way. Use Inspect > Measure between the new plane and a face to confirm before sketching.

Using points effectively#

Construction points are mostly anchors for sketches and for Point Along Path placements. Point Through Three Planes gives the corner of a virtual box, which is the right place to start a hole pattern that must stay at a nominal corner even after the corner is rounded off by a fillet. Point At Edge And Plane gives where a cable path pierces a bulkhead.

Failure modes and fixes#

Practice exercise#

Build a bracket where every feature hangs off construction geometry, then stress-test it.

1. Create a user parameter height = 60 mm and width = 40 mm (Modify > Change Parameters).
2. Sketch a width x width square on the XY plane and extrude it to height, so the body is 40 x 40 x 60.
3. Construct an Offset Plane from XY at height / 2, named "Mid". Construct an Axis Through Two Points along the body's top front edge endpoints.
4. Construct a Plane at Angle of 20 degrees about that axis, referenced to the top face. Sketch a 10 mm circle on it and Extrude Cut through the body.
5. Mirror the cut across the "Mid" plane.
6. Construct three planes along a 100 mm sketched spline using Plane Along Path at 0, 0.5 and 1.0 Proportional, then Absolute at 30 mm; compare positions.
7. Stress test: change height to 90 mm, then width to 55 mm. The Mid plane, angled holes and mirror must all follow. Then add a 3 mm fillet to the top edges and confirm nothing turns red. Finally, rebuild plane "Mid" from the top face and repeat the fillet to see how references to late faces behave.

Expected result: a parametric part that survives both dimension changes, and a clear idea of which references are stable.

Related#

• Mirror and Patterns
• Loft and Sweep (profile planes)
• Revolve (axes)
• Sketch basics (sketch planes)