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Quick Start

This guide takes you from a fresh install to a finished part exported as STEP. It should take about ten minutes.

Seamless CAD is in beta and sold for Windows. This guide applies to the macOS and Linux testing builds too — the add-on is the same.

1. Install

  1. In Blender, open Edit > Preferences > Add-ons > Install...
  2. Select the CAD_<version>_install.zip file
  3. Enable the add-on
  4. Press N in the 3D viewport to open the sidebar. A Seamless tab appears.

Blender 4.2 or newer is required. Development and testing are done on 5.1.

2. Start a session

Open the Seamless tab. Before anything else exists, the sidebar shows a single button:

  • Start Seamless CAD

Press it. This launches the geometry kernel and creates your first CAD part.

What is actually happening: shapes are not computed by Blender's mesh system. They are computed by OpenCASCADE (OCCT) in a separate process, and Blender draws the result. This is why the add-on ships an executable and why the first start takes a moment.

3. Understand the workspace

The Active CAD Workspace panel controls which part you are editing.

  • The dropdown selects the active part collection
  • Add New CAD Part creates another, independent part
  • The trash icon removes the active part

Everything in the panels below applies to the active part only. If the panels below are missing, no valid part is selected — pick one from the dropdown.

4. Create your first shape

Open the Create panel and press Box.

A box appears in the viewport, and a corresponding entry appears in the Feature Tree panel. These are the same object seen two ways: the viewport shows the computed result, and the Feature Tree shows the recipe that produced it.

The Create panel is organised in rows:

Row Contents
Solids Box, Cyl, Sph, Cone, Torus
Curves and profiles Curv, Plin, Arc, Surf, Slot, Poly, Gear, Helix, Rev
Swept shapes Sweep, Loft
Grouping Group ( , Group )
Sketching Start Sketch, on Face

5. Edit it after the fact — this is the point

Click the box's entry in the Feature Tree. The Active Property Editor panel below now shows its parameters. Change the width.

The shape rebuilds. Nothing was destroyed, and you can change it again.

This is what "non-destructive" means here, and it is the main reason to use this add-on instead of Blender's own modelling tools. A box you created twenty operations ago is still a box with editable dimensions.

You can also move a shape directly: select its proxy in the viewport and use G / R / S as you normally would in Blender. The geometry follows in real time.

6. Cut a hole

  1. Press Cyl to add a cylinder
  2. Position it so it passes through the box
  3. Select the cylinder in the Feature Tree, and in the Active Property Editor change Operation from Add (Fuse) to Subtract (Cut)

The Operation dropdown is how every shape combines with what came before it:

Value Effect
Base Start over. Everything above is discarded from this point.
Add (Fuse) Union with the shapes above. This is the default.
Subtract (Cut) Cut out of the shapes above.
Intersect (Common) Keep only the overlap with the shapes above.

The Feature Tree is evaluated top to bottom, so the cylinder subtracts from everything above it. Order matters — this is a history, not a layer stack.

7. Round the edges

  1. Open Modify & Pattern and press Fillet
  2. Selection mode starts on its own, already set to edges
  3. Click the edges you want in the viewport — they turn orange and stay selected
  4. Set the radius in the Active Property Editor

Add the modifier first, then pick. A selection is stored into the Fillet, so the Fillet has to exist before there is anywhere to put it. Entering selection mode with an ordinary shape active and clicking will not select anything — the add-on now says so instead of ignoring the click.

Hint: while in selection mode, hold Alt to use the normal Blender gizmo without leaving the mode. Shift-click adds to the selection instead of replacing it.

Chamf does the same with a flat cut instead of a round.

8. Control quality and speed

The Quality & Export panel governs how finely the kernel's result is converted into a mesh for display.

  • Linear and Curvature — display tessellation. Lower values are finer and slower.
  • Fast Modifier Preview and Live Boolean Preview — trade exactness for responsiveness while you drag. Turn these off if a preview looks wrong; the final result is always computed exactly.
  • Use High Quality Bake — a separate, finer setting used only when baking, so you can work at a coarse display quality without affecting output.

9. Roll back through history

Each Feature Tree row has a pin icon on the right. Pinning a row makes the part evaluate only up to that point; everything after it is greyed out and ignored.

Use this to inspect an intermediate state, or to keep a long history responsive while you edit something early in it. Unpin to restore the full tree.

Note that new operations are always added to the end of the tree, never at the pin. If you create a shape while a pin is set, it lands below the pin and is not evaluated — which looks like nothing happened.

10. Get the result out

Two ways, for two different purposes:

Bake to Mesh (Quality & Export > Bake to Mesh) converts the part into an ordinary Blender mesh. Use this for rendering, sculpting, or anything that needs Blender geometry. Enable Use High Quality Bake first if the result is for a render.

Export STEP (Quality & Export > Export > STEP) writes a real B-Rep STEP file (AP214 IS) for use in other CAD software. This preserves exact surfaces, not a triangulated approximation.

Scale: on export, 1 Blender unit is written as 1 mm. A 10-unit box arrives in FreeCAD or Fusion as a 10 mm box. Set your dimensions with that in mind.

STEP export does not currently carry part names, colours, or assembly structure. The geometry is exact; the metadata is not there.

Where to go next

  • Import STEP / Import SVG bring outside geometry into the tree
  • Start Sketch draws constrained 2D profiles on a plane or an existing face
  • Modify & Pattern holds Mirror, Array, Circular array, and linked instances
  • Cleanup (Unify) merges coplanar faces. It is deliberately opt-in — it is not applied automatically, because merging faces destroys the face identities that fillets and offsets refer to.

If something goes wrong

The Seamless tab is empty below the workspace panel. No valid part collection is selected. Pick one from the Active CAD Workspace dropdown, or press Add New CAD Part.

Hide Occluded Edges is greyed out. This is intentional. Faces only write depth when the WGPU overlay is off and opacity is fully opaque. Outside those conditions the setting would have no effect, so it is disabled rather than left as a control that silently does nothing.

A shape looks wrong while dragging, but correct when released. That is the fast preview. Turn off Fast Modifier Preview or Live Boolean Preview to always see the exact result.

Nothing updates after an edit. Press the refresh icon in Modify & Pattern > Topology to force a recompute.