Patch

Overview#

Patch creates a surface bounded by a closed loop of edges or sketch curves. It is the surfacing equivalent of "fill the hole". You use it to close holes on a surface body or repair missing faces on a solid body, and you can shape the fill with interior rails or points.

Patch lets you set the continuity condition (Connected, Tangent, Curvature) per boundary edge, which makes it central to high-quality surfacing.

Where to find it#

• Surface > Create > Patch
• Toolbar search (S): type "Patch".

Step by step#

Simple cap on an open shell#

1. Open a surface body with a hole (for example, the sides of a surface-extruded rectangle).
2. Start Patch.
3. Select the Boundary Edges that surround the area to patch. With Tangent Chain checked, all tangentially connected edges are selected automatically.
4. Set Continuity to Connected (G0) for a flat cap.
5. Click OK. A new surface body is created; stitch it to the shell if you want one quilt.

Patch with tangent edges#

1. Pick the boundary edges.
2. On the Feature tab, choose Tangent (G1) for edges where the new surface should leave the neighbor smoothly. Check Group Edges to set Continuity and Tangency Weight for all selected edges at once; uncheck it to list each edge in the table and set them separately.
3. Adjust the Tangency Weight to fine-tune the transition (available for Tangent and Curvature).
4. Examine with Zebra Analysis (see Curvature Analysis), or pick an Analysis Type on the dialog's Analysis tab to preview it in context.

Patch with guide rails#

1. Start Patch and select the boundary.
2. Select Interior Rails/Points to guide the patch. They shape the interior, for example a dome or crown line.
3. Autodesk's help lists no further per-rail options.

Options reference#

Tips and pitfalls#

Tip: Use the smallest possible boundary. Patching across large, high-curvature gaps produces wobbles because the patch has too few degrees of freedom. Break a big hole into two or three patches with logical edges.

Tip: After you select a boundary with tangent condition, hide the neighboring faces briefly to see the patch itself and check for flipped or twisted behavior.

Warning: A patch is a new, independent body. It does not stitch itself to the surrounding shell. Run Stitch afterward, and check that the tolerance does not hide a real gap.

Warning: The boundary edges must form a closed loop connected end to end. If the selection is not accepted, look for gaps or tiny edges and clean them up first (Stitch or sketch cleanup).

Warning: Curvature (G2) continuity on all edges of a small patch can overconstrain it, producing bumps. Use Tangent on most edges and Curvature only where the eye will notice the transition.

Tip: For a patch in a hole of an imported solid where the surrounding geometry is flat, plain Connected continuity is fine, and produces a simpler surface.

What Patch does#

According to Autodesk's help, Patch closes holes on a surface body or repairs missing faces on a solid body. You select the boundary edges that surround the area and then choose how the patch meets each edge: the Continuity options run from positional (G0) through tangent (G1) to curvature (G2). The result is a new surface body that you can stitch to the adjacent surface faces; Autodesk suggests Patch followed by Stitch to make a watertight solid.

Worked example: capping a 28 mm bottle neck#

A shoulder surface leaves a circular open rim of 28 mm diameter. The heights below are illustrative, not Autodesk figures.

1. Run Patch and select the rim edge.
2. G0 (Connected) gives a flat cap: fine for a hidden closure or a thread start, but the rim shows a crease.
3. G1 (Tangent) gives a smooth dome whose height depends on the tangent angles. If the neck wall is vertical at the rim, a tangent patch is forced to leave vertically and domes up; the dome height depends on the Tangency Weight.
4. G2 (Curvature) also matches the neighbor's curvature. Compare zebra results: per Autodesk, stripe edges that align but meet at a sharp angle indicate G1, and stripes that are smooth throughout indicate G2.
5. If the dome is too tall, reduce the Tangency Weight or add an Interior Rail through the desired apex.

For a flat bottom of a vessel, use G0 and accept the edge; the manufacturing process usually adds a radius there anyway.

Choosing continuity per edge#

Different edges can use different continuity: you might set G1 on the long sides and G0 on a short side where a hard edge is wanted.

Failure modes and fixes#

Patch versus other fill tools#

• Loft between two profiles gives control over both, better for a through shape.
• Boundary Fill creates volumes, not faces.
• Extend plus Trim can fill a gap that is nearly parallel.
• Ruled Surface fills a gap with straight rulings and is quick for flat or developable regions.

Prefer Patch when the opening is closed and roughly flat or gently domed; for large or strongly shaped openings, interior rails or Loft are more controllable (general guidance).

Workflow advice#

1. Clean the boundary before patching: stitch edges, remove micro-faces.
2. Start with G0 and verify the patch shape, then raise continuity one step at a time.
3. Check with Zebra and Curvature Comb on a section through the patch.
4. Stitch the patch to the body and confirm the volume and free edge count.
5. If the patch looks wrong at G2 but right at G1, the neighboring surface curvature is the issue, so fix that first.

Reading the patch with a section#

A patch can look right in the shaded view and still be wrong in profile. Cut a section sketch or use Section Analysis through the patch center in two perpendicular directions. Measure the apex height against your intent: for a 28 mm opening, a 3 mm dome reads as gentle and an 8 mm dome as a button (an illustrative judgment, not an Autodesk figure). If the section shows an S-shaped wiggle rather than a single arc, the continuity demands at opposite edges are fighting; reduce one side to G0 or add a rail. A comb on the section line shows the curvature distribution; a good dome shows teeth of roughly equal length across the middle.

Patching solids#

Patch also repairs solid bodies that are missing a face (typically after Delete Face or an import problem). Select the edges of the opening on the solid, and the patch is created as a surface that you then Stitch to the body to close it. For small openings on solids, check that the result is a valid solid by confirming a positive volume in Properties.

Practice exercise#

1. Sketch a 40 mm circle on the Top plane and surface-extrude it upward 20 mm (a cylinder wall, open on both ends).
2. Patch the top rim with Connected continuity: you should get a flat disk.
3. Undo the patch, then patch again with Tangent continuity and a large weight. The result should dome or flex according to the wall direction (for a vertical wall, tangent continuity tries to continue upward, so expect a tall, bulged cap).
4. Stitch the best result to the cylinder wall. Open Zebra Analysis and compare the Connected and Tangent versions at the rim.

Expected: the tangent patch shows aligned stripe edges across the rim; the connected one shows stripe edges that do not align.

Stretch challenge#

Build a 60 mm diameter cylinder surface 40 mm tall, open at the top. Patch the top at G0, G1 and G2 and extrude a sketched dome 10 mm high as a reference. Measure the apex height of each patch and compare. Add a guide rail through a sketch point 6 mm above the rim and observe how it changes the apex. Expected result: three apex heights recorded (G0 flat at 0 mm, G1 and G2 domed), and a rail version at 6 mm, with zebra stripes showing the continuity improving from G0 to G2.

Related#

• Stitch and Unstitch
• Continuity G0 to G3
• Surface Repair
• Curvature Analysis