Form Workspace Overview (T-Splines)

Overview#

The Form environment (historically called the Sculpt workspace, and still called that in older tutorials and forum posts) is where you build organic, freeform shapes in Fusion. Instead of sketching profiles and extruding them, you push and pull a coarse "control cage" and Fusion computes a smooth surface over it. The underlying technology is T-splines, a kind of subdivision surface that is converted to a precise boundary representation (BRep) when you finish.

Use Form when the shape you want is hard to describe with sketches and fillets: ergonomic handles, helmets, vases, character-like shapes, organic enclosures, or smoothly blended transitions between unlike cross-sections. Do not use it for prismatic, dimension-driven parts like brackets and plates; those are faster and more precise with sketches and the Solid tools.

Key vocabulary:

Where to find it#

Autodesk reorganized the UI over the last few years. In current builds the path is as follows:

• Current Fusion: the Form tools live in the Design workspace. On the Solid tab, choose Create > Create Form. This opens a contextual Form tab (with the Finish Form button at the far right). The same tab appears when you double-click an existing Form feature in the timeline.
• Older versions: a separate Sculpt workspace was selected from the workspace drop-down. Many tutorials still show this layout.
• Timeline: Form work appears in the timeline, but Autodesk notes that T-spline operations are not recorded in history in the same way as solid and surface operations. You can go back in the timeline and adjust your T-spline shapes, and the changes are recomputed when you select Finish Form.

The Form tab is organized into panels. The command names below were checked against Autodesk's help:

• Create: the primitives (Box, Plane, Cylinder, Sphere, Torus, Quadball, Pipe, Face) and Extrude, Revolve, Sweep, Loft.
• Modify: Edit Form, Edit By Curve, Insert Edge, Subdivide, Insert Point, Merge Edge, Bridge, Fill Hole, Erase and Fill, Weld Vertices, Unweld Edges, Crease, Uncrease, Bevel Edge, Slide Edge, Smooth, Cylindrify, Pull, Flatten, Straighten, Match, Interpolate, Thicken, Freeze and Unfreeze. Delete (see "Delete T-Spline geometry" in the help) is also available.
• Symmetry: Mirror - Internal, Circular - Internal, Mirror - Duplicate, Circular - Duplicate, Clear Symmetry and Isolate Symmetry (covered in the symmetry page).
• Utilities: Display Mode, Repair Body, Make Uniform, Convert and Enable Better Performance / Better Display.
• Selection: the Edit Form dialog carries the Selection Filter (Vertex, Edge, Face, All, Body) and selection options such as Grow/Shrink, Loop and Ring.

Step by step#

This first walk-through gets you comfortable with the environment before any real modeling.

1. Open a new design. In the Solid tab, choose Create > Create Form. The Form tab replaces the Solid tab.
2. Choose Create > Box. Click a plane (the origin planes work) and drag out a rectangle, then click again to set the height. In the dialog, set Length Faces, Width Faces and Height Faces to 2 each. Leave Symmetry at its default for now.
3. Click OK. You now see a blobby, rounded box: the smooth surface lying inside a cage of 2x2x2 faces per side.
4. Open Utilities > Display Mode and cycle through the modes. Box shows the control points (cage), Control Frame shows the rounded surface with the control frame around it, and Smooth shows only the rounded surface. Shortcuts are Alt+1/2/3 on Windows and Control+1/2/3 on macOS. Control Frame is the usual working mode.
5. Choose Modify > Edit Form. Click a face on the cage. A manipulator with translate, rotate and scale handles appears. Drag an arrow to push the face out and watch the smooth surface follow.
6. Click on a vertex and then on an edge to see how the selection types behave. Hold Ctrl (Cmd on macOS) to select multiple items. Double-click a face or edge to select a loop (see the Edit Form page for loop and ring selection).
7. Click Finish Form in the top right. If the Form body is closed (watertight), you get a solid body; if it has open edges you get a surface. Check the browser to see the result.

Options reference#

Display and selection options you will touch constantly:

Other behaviors worth knowing:

• History. T-spline operations are not recorded in history the same way solid operations are, but you can go back in the timeline, adjust your T-spline shapes, and the changes are recomputed when you select Finish Form.
• Units and scale. Form geometry uses your design units. Primitive sizes are real dimensions, which matters later when you combine the form with solid features or 3D print it.
• Control, not interpolation. The smooth surface does not pass through cage vertices; it is pulled toward them. Dense cage means more local control and also more work.

Tips and pitfalls#

Tip: Start with the fewest faces you can. Every extra cage face you add is one more thing to push around and one more place for ripples. Add detail only where the shape demands it, using Subdivide or Insert Edge.

Tip: Switch to Control Frame and rotate the model often. A shape that looks right from the front can have a flat or lumpy area from another angle.

Tip: Keep the cage mostly quads with evenly sized faces. Large size differences between neighboring faces produce uneven curvature.

Warning: A Form body that has failed in Finish Form is almost always a cage topology problem (overlapping faces, non-manifold edges, zero-area faces, or inverted normals). Run Repair Body and inspect the highlighted problem region rather than trying to push through.

Note: not confirmed in Autodesk's documentation: whether Form is included in every licence tier (including Personal use). Check Autodesk's current licence comparison.

Tip: Form is excellent for concept shapes, but remember that you can convert the finished result to BRep and then apply ordinary fillets, shells, holes and parametric dimensions. A good hybrid workflow is a Form for the organic skin and solid features for the mechanical interfaces.

How the control cage relates to the surface#

The single most useful mental model in Form is that the cage is a set of influences, not a skeleton the surface sits on. Each cage vertex pulls the surface toward itself with a weight that falls off across the neighbouring faces. That has four practical consequences you will meet in every model.

1. Shrinkage. A smooth surface is always slightly inside the cage in convex regions. A cube cage with 2 x 2 x 2 faces makes a pillow-shaped blob that is noticeably smaller than the cage. Do not size a form by its cage; read dimensions off the smooth surface with Inspect > Measure.
2. Locality. Moving one vertex mainly affects the faces immediately around it. Moving a whole row of vertices is how you change a long curve without producing a bump.
3. Density equals stiffness. Where cage faces are small and close together, the surface follows the cage tightly and resists broad reshaping. Where cage faces are large, the surface is loose and easy to bend. Plan density the way you plan fillet radii: tight where you want a small radius, loose elsewhere.
4. Creases and parallel edges. Because the surface is pulled toward every vertex, putting two edge loops very close together (for example 0.5 mm apart on a 100 mm part) makes the surface turn sharply between them. That is the manual alternative to a Crease and is covered on the creases page.

Worked example: you want a 40 mm wide pebble. If you build a Box of 40 mm with 2 faces per side and look at it in Smooth mode, the smooth body will measure noticeably less than 40 mm across, because the surface does not reach the cage corners. Scaling the cage up brings the smooth width back to 40 mm. With more faces per side the shrinkage is smaller, because more cage points lie closer to the surface. This is general behaviour of subdivision surfaces, not an Autodesk figure: measure your own result after every large change rather than trusting the cage.

Choosing the starting approach#

If a shape combines mechanical and organic features, plan to make the organic skin in Form and everything with a tolerance (screw bosses, snap fits, seating faces) afterward with Solid features. Trying to hit exact dimensions by moving cage vertices wastes time.

Working habits that prevent rework#

• Name the Form feature. Rename the Form feature in the timeline when the design has more than one (for example "Housing skin"). Edits made when you double-click the wrong Form feature are a common source of confusion.
• Save a version before big topology changes. Subdivide, Bridge and Delete change the cage structure. Fusion's undo works inside the open Form, but once you finish and build features on top, topology changes may break references.
• Check from three directions. After each major move, orbit to front, side and top, then switch to Smooth only. Silhouette problems hide inside Control Frame view.
• Use analysis early. Zebra Analysis under Inspect shows reflection stripes on the smooth surface. Parallel, flowing stripes mean good continuity; kinked stripes often point to cage faces of very different sizes or a misplaced star point (general guidance).
• Know the licence boundary. Licence entitlements for Form are not stated in the help, so confirm them in Autodesk's current licence comparison.

Troubleshooting the first hour#

Practice exercise#

Build a pebble and prove you understand cage versus surface, then measure the difference numerically.

1. Create a Sphere (Create > Sphere), 50 mm across, 4 faces in each direction. In Control Frame mode, use Inspect > Measure on the smooth surface to read its width, then compare it with the cage width. Record both numbers; the smooth width is smaller.
2. Choose Modify > Edit Form, select one cage face and pull it outward about 10 mm. Observe how many neighbouring faces respond.
3. Select a single vertex near the top and move it down 3 mm. Notice the surface does not touch the vertex.
4. Undo, then select the whole top row of vertices and move it down 3 mm instead. Compare the smoothness with step 3. Rows give a cleaner curve than single vertices.
5. Switch to Smooth only and judge the shape from front, side and top.
6. Click Finish Form, then run Inspect > Zebra Analysis on the body. Look for kinked stripes near the face you pulled. Double-click the Form feature to go back and even out the area if needed.

Expected result: a closed, smooth, slightly irregular solid body in the browser, a Form feature in the timeline you can double-click to resume editing, and two recorded measurements showing the cage is larger than the surface. If the finished result is a surface rather than a solid, the form has an open edge, so check that no faces were deleted.

Related#

• Form primitives (next page in this section)
• Edit Form and selection
• Finish Form and conversion
• Section index for mesh topics later in this section