Overview#
Offset (Surface > Create > Offset) creates a duplicate of a surface at a given distance along its normal. Use it for parallel skins, shelling by hand, and creating clearance surfaces.
Ruled (Surface > Create > Ruled) builds a surface from edges on a solid body, surface body or sketch, extending it at a specified distance and angle. It generates flanges, parting-line skirts, and draft-based walls quickly and with predictable geometry.
Where to find it#
- Surface > Create > Offset
- Surface > Create > Ruled
- Toolbar search: S, then type the name.
Step by step#
Offset#
- Start Offset in the Surface tab.
- Select one or more faces or a surface body. Chain Selection picks tangent-connected faces together.
- Choose an Offset Type: Sharp Offset (sharp offset corners) or Rounded Offset (rounded offset corners).
- Specify the Distance by dragging the manipulator or entering an exact value. Check the preview to confirm the direction.
- Choose Operation: New Body, or New Component (Hybrid Design type only).
- Click OK. A new surface body appears at the offset distance.
Ruled Surface#
- Start Ruled.
- Choose the type: Normal (normal to the face of the selected edges), Tangent (tangent to the face of the selected edges) or Direction (in a direction you select).
- Select the Edges on a solid body, surface body or sketch that the ruled surface extends from.
- Specify the Distance and Angle, using the canvas manipulator handles or exact values.
- Choose the Operation: New Body or New Component.
- Optionally pick an Analysis Type on the Analysis tab, then click OK.
Optional checkboxes per Autodesk's tips: Tangent Chain controls the selection set dynamically, Mitered Corners creates sharp instead of rounded corners, and Alternate Faces flips the direction or angle when edges share more than one face.
Typical use: select the outer edge of a lid, set Tangent type with a distance of 5 mm to create a skirt that continues tangent to the surface.
Options reference#
Offset#
| Option | What it does | Notes |
|---|---|---|
| Faces / Surface | Geometry to offset | Faces or whole surface bodies |
| Chain Selection | Includes tangentially connected faces | Uncheck to select individual faces |
| Offset Type | Sharp Offset or Rounded Offset | Controls the corners |
| Distance | Offset distance | Manipulator or exact value |
| Operation | New Body, or New Component | New Component: Hybrid Design type only |
Ruled Surface#
| Option | What it does | Notes/default |
|---|---|---|
| Type: Tangent | Surface is tangent to the face of the selected edges | Good for continuing a skin |
| Type: Normal | Surface is normal to the face of the selected edges | Good for flanges and walls |
| Type: Direction | Surface runs in a direction you select | Useful for parting-direction skirts |
| Edges | Edges the surface extends from | On a solid body, surface body or sketch |
| Distance, Angle | Extent and tilt of the ruled surface | Manipulators or exact values |
| Tangent Chain | Dynamically controls the selection set | |
| Mitered Corners | Sharp corners instead of rounded corners | |
| Alternate Faces | Flips direction or angle when edges share more than one face | |
| Operation | New Body or New Component |
Tips and pitfalls#
Tip: Ruled Surface is the cleanest way to build parting-line surfaces for mold design. Select the silhouette edge, choose Direction or Normal, and set a distance larger than the mold block.
Tip: Offsetting faces of a solid is for surface output. To thicken a solid wall, use Shell or Press Pull instead.
Warning: Offsetting a surface by more than its smallest concave radius produces self-intersections and cusps. The preview may look fine while the result fails. Inspect inside corners.
Warning: The offset direction follows the face normal, which can be reversed on imported or flipped faces. Autodesk's help does not state a sign convention, so check the preview, not the sign you typed.
Warning: Ruled surface along an edge with sharp corners can produce twisted geometry at the corner unless the corner type fits. Preview before accepting.
Tip: With Chain Selection off, faces are offset individually; stitch the result if you need a single quilt.
Offset in practice: what it can and cannot do#
Offset creates a new surface at a fixed distance from selected faces or surfaces. It is the surfacing tool for shells, skins, and clearances.
Key behaviors:
- The direction depends on which way the face normal points. Check the preview before accepting.
- The offset of a curved surface is only well behaved when the offset distance is smaller than the tightest radius of curvature on the side you offset toward. Offsetting a 10 mm radius cylinder inward by 12 mm cannot work: the surface would collapse through its axis and invert. Offsetting outward by 12 mm gives a clean 22 mm radius.
- Offsetting several adjacent faces together keeps them connected; separate offsets of each face leave gaps at the seams.
- The Operation is New Body, or New Component in the Hybrid Design type. For surfaces, New Body is normal.
Worked example: a 2 mm gap shell for a cover#
A cover must clear a component by 2 mm. Offset the outer faces of the component by 2 mm outward as new surface bodies, stitch them, and use that as the inner boundary for the cover. If the component has a 1.5 mm fillet radius on a corner, the 2 mm outward offset of that corner has radius 3.5 mm, which is fine. If you offset inward by 2 mm instead, the 1.5 mm fillet cannot be offset (2 is greater than 1.5), and the command will fail or produce a degenerate region at that corner; reduce the offset to 1.4 mm or edit the fillet.
Ruled Surface: types and when each applies#
A ruled surface is created by sweeping straight lines from an edge. It is quick for flanges, run-off faces, and parting surfaces.
| Type | Behavior | Best for |
|---|---|---|
| Tangent | Tangent to the face of the selected edges, at the distance and angle you set | A flange that continues smoothly off a curved face |
| Normal | Normal (perpendicular) to the face of the selected edges | A wall that stands straight off a surface |
| Direction | Runs in a direction you select | A mold parting surface in the pull direction |
The inputs are a chain of edges, a distance, and an angle (measured from the reference). Because the rulings are straight lines, a ruled surface from a curved edge may be developable or may twist; if the chain is not planar you will see the twist. Start with a short distance and extend it.
Worked example: a parting surface for a mold#
A part has a perimeter edge loop on its widest section. Create a Ruled surface of type Direction, direction perpendicular to the pull axis, distance 25 mm. This gives a flat skirt around the part, which you can then use with Split Body to divide a mold block. If the loop is irregular, the ruled surface may self-intersect at tight inside corners when the distance is greater than the corner radius; reduce the distance or try Mitered Corners.
Failure modes and fixes#
| Symptom | Cause | Fix |
|---|---|---|
| Offset fails with an error | Distance exceeds a tight radius, or a face is degenerate | Reduce the distance, remove tiny faces, or offset in steps. |
| Offset surface has gaps between faces | Faces offset individually or the tolerance is too tight | Select all faces together; stitch the result with an adequate tolerance. |
| Offset goes the wrong way | Normal direction is opposite | Check the preview, and try a negative distance or Reverse Normal. |
| Ruled surface twists unexpectedly | Non-planar edge chain with a large angle | Reduce the angle, or build the surface in segments. |
| Ruled surface overlaps itself at a corner | Distance larger than the local corner radius | Reduce distance, or try Mitered Corners. |
| Result is a single sliver | Edges chosen are collinear or very short | Pick the longer chain; check the units. |
Comparing with similar commands#
- Offset Face (in the Solid tab) moves solid faces; Surface Offset creates a separate surface body.
- Thicken makes a wall from a surface, so if you need a 2 mm skin you can instead offset and Thicken.
- Extrude with a taper creates simple ruled walls from a sketch; Ruled Surface is for walls from existing edges.
Workflow advice#
- Offset after the source is stable; offsets update with the source but can fail when the source topology changes.
- Name the offset bodies by their function ("Clearance_2mm").
- Check with Measure that the distance between a source point and the offset is the value you entered; sign errors are the usual mistake.
- For stacks of offsets (0.5, 1.0, 1.5 mm layers) make each from the original, not from the previous one, so errors do not accumulate.
Practice exercise#
- Surface-loft or surface-extrude a gentle curved panel.
- Offset it 3 mm to each side (two operations). You now have two parallel skins.
- Select the free edges of the outer skin and create a Ruled Surface of type Normal with 3 mm distance, aiming toward the inner skin, to close one edge. Repeat on the other three edges.
- Stitch everything. Expected: a closed quilt that becomes a solid of constant 3 mm wall thickness (a hand-made shell).
Stretch challenge#
Make a 40 mm diameter, 30 mm tall cylinder with a 2 mm bottom fillet. Offset its outer faces outward by 3 mm and then inward by 1 mm and observe the result. Offset inward by 2.5 mm and note the failure at the fillet. Then add a Ruled Surface of type Tangent off the top rim, 10 mm long at 30 degrees, and measure the rim diameter at the end (it should be 40 plus 2 x 10 x sin(30 degrees) = 50 mm if the angle is measured from the rim's plane and the flange leans outward; confirm how the angle is measured in the dialog). Expected result: a short table of offsets with pass/fail, and a flange of measured outer diameter close to the computed value.
Related#
- Thicken and Solid From Surface
- Trim and Untrim
- Extend