Mirror and Patterns

Overview#

Repetition is the main reason to use CAD. Fusion offers:

• Mirror: reflect objects across a plane.
• Rectangular Pattern: repeat in one or two linear directions.
• Circular Pattern: repeat around an axis.
• Pattern on Path: repeat along a curve.

Each can duplicate Features, Faces, Bodies, Components, or Construction Geometry (planes, axes and points). Choosing the right type matters: in general experience patterning features is fastest and lightest; patterning faces is flexible but fragile; bodies and components are for separate parts.

Where to find it#

• Workspace: Design.
• Tab / panel: Solid tab > Create > Mirror; Solid tab > Create > Pattern drop-down > Rectangular Pattern, Circular Pattern, Pattern on Path.
• Shortcut: none listed in Autodesk's shortcut reference.
• Sketch equivalents: the Sketch tab has its own Mirror, Rectangular Pattern, and Circular Pattern for 2D geometry (a different tool with a similar dialog).

Step by step#

Mirror#

1. Create > Mirror.
2. Select the Object Type (Parametric Modeling mode only): Faces, Bodies, Features, Components, or Construction Geometry.
3. Select the Objects (timeline features or items in the canvas).
4. Select the Mirror Plane (a plane or planar face).
5. In Parametric mode choose the Operation: New Body, or Join to merge the mirrored body with the original if they intersect.
6. OK.

Rectangular Pattern#

1. Create > Pattern > Rectangular Pattern.
2. Choose the Object Type and select the objects.
3. Choose Axes: select one or more linear objects (an edge, axis or sketch line) to distribute along.
4. Set the Distribution (Extent or Spacing), Quantity, and Distance for each axis, and the Direction (One direction or Symmetric).
5. Optionally check Suppression and uncheck individual instances in the canvas.
6. OK.

Circular Pattern#

1. Create > Pattern > Circular Pattern.
2. Select objects, then the Axis (a linear or circular object, such as a construction axis, cylindrical face or edge).
3. Set the Distribution: Full (360 degrees), Partial (one direction from the source to a set angle) or Symmetric (both directions from the source to a set angle), then enter Quantity and, for Partial and Symmetric, the Angle.
4. OK.

Pattern on Path#

1. Create > Pattern > Pattern on Path.
2. Select objects and a Path curve.
3. Set the Distribution (Extent or Spacing), Distance, Quantity and Direction (One direction or Symmetric).
4. Choose Orientation: Identical (all instances match the source object) or Path Direction (each instance is oriented relative to its position along the path).
5. Optionally set the Start Point (a percentage offset of the first instance; you can also drag it along the path).

Worked example: bolt circle#

1. Make a 80 mm diameter disc, 10 mm thick.
2. Create a hole 6 mm diameter at 30 mm from the center on the top face.
3. Circular Pattern: type Features, select the hole, axis = disc's cylindrical face, Quantity 6, Angle 360.

You get six equally spaced holes. Changing Quantity to 8 updates the pattern.

Options reference#

The Compute setting matters for performance. Autodesk describes Optimized as the fastest: it creates identical copies by patterning the feature's faces, but it cannot create overlapping occurrences or occurrences that intersect faces other than the original feature's faces. Identical creates identical copies by replicating the results of the original features; use it when Optimized is not available. Adjust creates potentially differing copies by calculating the extents or terminations of each occurrence individually, so features that terminate on a face keep their design intent; it is the slowest, is not available for solid bodies in an open or surface state, and if it meets a planar face the operation terminates with a result different from the original.

Tips and pitfalls#

Tip: Pattern features rather than bodies whenever possible; the file stays small and the timeline stays simple.

Tip: Mirror half a symmetrical part to guarantee symmetry; edits made to the original half automatically propagate.

Warning: Feature patterns fail when an instance would run off the face or into geometry that did not exist when the original feature was made. Switch the compute setting to Adjust, or pattern bodies.

Warning: Mirror with Bodies creates a new body by default; choose the Join operation (Parametric mode) or use Combine if you want the result merged.

Warning: Patterning faces can fail after upstream changes because face references shift. Prefer features.

• For a mirror plane that does not exist, create a Midplane between two faces (see Construction Geometry).
• A rectangular pattern can use an arbitrary edge as its direction; no need to align to axes.
• In Pattern on Path, make sure the Path selection covers the whole curve you want to follow.
• If Spacing times Quantity overshoots the path length, instances run off the path. Use Extent for even coverage (general guidance).
• Pattern parameters can be driven by named parameters: set Quantity to n_holes for easy design tables.
• Components can be patterned for assemblies; each instance is a new occurrence of the same component (changes to one affect all).

Choosing a pattern type#

A feature pattern that includes a Join to the host body only works when each instance also lands on the host. If instance 7 of a boss falls partly off the edge of the plate, the whole pattern can fail. Suppress that instance with the Suppression checkboxes, or use Adjust.

Numbers for linear patterns#

The Distribution setting changes what your numbers mean:

• Extent: the Distance is the total from the first instance to the last. Quantity 5 with Extent 80 mm spreads the instances evenly over 80 mm: 0, 20, 40, 60 and 80 mm (spacing 80 / (5 - 1) = 20 mm).
• Spacing: the Distance is between neighbors. Quantity 5 with Spacing 20 mm gives the same result, but changing Quantity to 6 now extends the pattern to 100 mm, whereas with Extent it re-divides 80 mm into 16 mm steps.

Choose Extent when the pattern must fit a fixed envelope (a hole row across a 100 mm panel); choose Spacing when pitch is the design intent (a 2.54 mm header pin pitch, a 25 mm DIN rail slot pitch).

Numbers for circular patterns#

Full with Quantity n puts instances every 360 / n degrees: 6 holes are 60 degrees apart, 5 holes 72 degrees. A bolt circle of diameter 60 mm with 6 holes has hole centers 30 mm from the axis and a chord between neighbors of 30 mm (equal to the radius, since the angle is 60 degrees). For a Partial pattern of 120 degrees with Quantity 4, the angle should be divided across 3 gaps, giving 40 degrees apart (confirm in the preview). Symmetric distributes instances to both sides of the source.

Pattern on Path orientation#

Orientation Identical orients every copy to match the source object, as for evenly placed fence posts along a curved wall. Path Direction orients each copy relative to its position along the path, as for teeth on a chain. On a closed path, check whether the last instance lands on the first and reduce the extent if it does.

Mirror details#

• Mirror Features mirrors timeline features, so the mirrored half follows when you change the original's dimensions (general behavior of parametric features).
• Mirror Bodies creates a new body; in Parametric mode set Operation to Join to merge it with the original if they intersect, or run Combine.
• Cuts generally affect the bodies that are visible when the feature is created, so hide or show bodies before you mirror.
• Mirror can also reflect Components and Construction Geometry (planes, axes and points).

Worked example: a vented lid#

1. Sketch a 120 x 80 mm rectangle, extrude 3 mm.
2. Cut a slot 30 x 3 mm, 10 mm from the left and 10 mm from the front edge.
3. Rectangular Pattern the slot along the 120 mm direction: Spacing 8 mm, Quantity 4. The slots span 24 + 3 = 27 mm, from x = 10 mm to x = 37 mm.
4. Mirror the slot features across a plane through the middle of the plate (create a Midplane at x = 60 mm) to put a matching set on the other side. Check the result: 8 slots, symmetric.
5. Create a user parameter slot_n = 4 and drive the quantity. Setting it to 6 would put the last slot at 10 + 5 x 8 = 50 mm, still before the 60 mm mirror plane, so it succeeds; setting it to 16 puts the last slot at 10 + 15 x 8 = 130 mm, off the plate, and fails.

Failure modes and fixes#

Practice exercise#

Build a vented junction box lid and a bolt circle, and test where the patterns break.

1. Model a 100 x 60 x 10 mm plate with one 5 mm hole 10 mm from a corner.
2. Rectangular Pattern the hole using Distribution Extent: first axis Quantity 4 over 80 mm, second axis Quantity 3 over 40 mm. Calculate the spacing before checking (26.67 mm and 20 mm). Switch Distribution to Spacing at 20 mm and note how the length changes when Quantity changes.
3. Suppress the two middle instances in the second row. Then Mirror the resulting features across a Midplane of the plate.
4. On a second 80 mm diameter disc, 10 mm thick, add a 6 mm hole 30 mm from the center. Make a Circular Pattern, Full, Quantity 6. Check with Inspect > Measure that adjacent centers are 30 mm apart. Change to Partial, 120 degrees, Quantity 4, and verify the spacing is 40 degrees.
5. Create a Pattern on Path using a 100 mm arc spline and a small rib. Compare Identical and Path Direction.
6. Create a parameter n_holes and drive the Circular Pattern Quantity from it. Set it to 12 and find the maximum value at which holes (6 mm) stay separated on the 30 mm radius (circumference 188 mm; at 6 mm diameter plus 2 mm wall, the limit is about 23).

Expected result: two patterned plates, a mirrored feature set, a path pattern, and a numeric limit you derived and then tested.

Related#

• Hole and Thread
• Construction geometry (mirror planes, axes)
• Move/Copy
• Extrude