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Parts and Assemblies

A part is one thing you can move: a body together with the sketches and workplanes that define it. The body is a real mesh object, and each sketch stays pure source whose geometry is realised on it, which is why a part exports, applies and edits like any other mesh.

An assembly is a group of parts you can move as a whole. Both are just object parenting, so the outliner shows the real structure and you edit it there.

In the outliner

The outliner is where parts live. It shows two things at once: collections group each part, and objects nest under the object that carries them.

  • Scene Collection
    • Origin — the shared XY / XZ / YZ datum planes
    • Bracket — an assembly collection
      • Plate — a part collection
        • Plate — the part's body: a mesh, carrying the features
          • Plate XY — the plane its sketch was drawn on, now the part's XY
            • Plate Sketch — the source the body is built from
          • Plate XZ, Plate YZ — made when the picker first offered them
          • Workplane — on a face of Plate
            • Plate.001 — a cutter, with its own sketch beneath it
      • Pin — a second part in the same assembly
    • Body — global: drawn on a datum, not yet solid
      • Body Workplane — its own plane, nameless until it becomes a part

A new body is called Body, or takes the name of the part it joins, and its plane and sketch follow the name it has: rename the body and they rename with it.

Read the nesting, not the collections: Plate.001 is part of Plate because it hangs under it, through the workplane it sits on. The collections follow that structure, they do not define it. Moving Plate moves everything beneath it; moving Bracket moves both parts.

This is also why parenting is how you change membership: drag Body onto Plate and it becomes one of its features.

Moving a part

Leave the sketch (parts are moved in Object Mode), select the part's body, the mesh, and press G or R. Its sketches, workplanes and cutters follow. Scale is locked: the solver treats a sketch's plane as a rigid frame, so a scaled part would draw and solve at different sizes.

The object you grab is the body, so you are moving the geometry you see rather than a helper object. The sketches that shape it are pinned within it.

What belongs to what

Membership is never a mode you switch. It follows from what you drew on, and it is settled when the sketch becomes solid:

You do this Result
Sketch on a body's face or on a part's workplane Joins that part right away
Sketch on a global XY/XZ/YZ plane Stays global: no part, free to move
Extrude or revolve with nothing to cut Its body roots a part of its own
Extrude or revolve that cuts an existing body Joins that body's part, as a cut feature
Editing what a body is made of Edit its sketch; the body follows
A cut reaching bodies in several parts Belongs to no part; if those parts share an assembly it becomes a feature of the assembly

A cut has to travel with the body it cuts, which is why it joins that part: were it left behind, moving the body would silently change the result.

Making a part by hand

Parts normally appear on their own, but imported geometry never passes through a sketch tool. Select it and use Make Part in the Tools panel: the active object roots the part and anything else selected joins it. With a part already active it simply takes the rest of the selection in, which is how you add a body to an existing part.

Part workplanes

A sketch that is not in a part sits on a plane of its own, where you drew it. When it becomes solid, that same plane becomes the new part's XY: a part's XY is always the plane its first sketch was drawn on, and XZ and YZ appear the first time the picker offers them.

Select a part and the Add Sketch tool shows its planes, drawn smaller, in place of the scene's, so a part that has been moved or rotated is sketched in its frame rather than the world's. Deselect to get the scene's planes back, which is also how you start a new part.

Sketching on a face makes a workplane for that face, and you can sketch on any empty you place yourself. Those are the only other planes: nothing creates a plane per sketch.

Changing membership by hand

Parenting is membership, so the override is Blender's own gesture: Ctrl+P in the viewport, or a drag in the outliner.

  • Parent a sketch onto a part's body to make it a feature of that part.
  • Unparent it to make it global again.
  • Parent a part onto an assembly root to put it in that assembly.

A sketch that becomes a feature is pinned in place; one that leaves a part is free to move again. Objects you made yourself keep their freedom either way.

Deleting a part's body does not scatter the rest: its workplanes and sketches keep their place and the next sketch in the part takes over as its body. The same applies to an assembly, whose parts simply stand on their own again.

Assemblies

Select the parts you want to group and use Add Assembly in the Tools panel (shown when no sketch is active). With nothing selected it creates an empty assembly at the 3D cursor, to be filled by dragging parts into it. Parts stay individually movable inside an assembly, and assemblies can contain assemblies.

Copying and reusing a part

Duplicate Part makes an independent copy of the whole part, with the workplanes, sketches and cutters that shape it. It is on Shift+D while the selection belongs to a part; everything else still gets Blender's own duplicate, which copies only what you selected, so a body duplicated that way would arrive without its cutters. Turn both shortcuts off in the add-on preferences if you would rather keep Shift+D and Alt+D as they were.

Instance Part places another copy of the same part: at the 3D cursor from the panel, or on the original and ready to move on Alt+D. Select an assembly instead and it places a copy of the whole assembly, which is how one sub-assembly ends up in several places. There is still only one part: each placement renders it, so editing the part updates every copy at once, and a copy costs almost nothing.

Placements are not edited where they stand, because they hold no geometry of their own: to change anything, edit the part itself. A placement joins whatever assembly the part is in, and it is not a part itself, so it never collects sketches of its own.

Editing a part's sketches

Right-click a part in the viewport and Edit Sketch opens the sketch that made it. When the part holds several sketches you get them as a menu, body first: that is also the way to a cutter, which cannot be clicked while it is hidden.

The sketch list in the Sketcher panel shows the same sketches, scoped to the part you have selected.

Cutter display

A cutter tells you what it is doing:

  • Hidden while it is cutting a body in its own part (its solid would sit over the result). Activate it from the sketch list to edit it.
  • Wireframe when it cuts across parts, or when it means to cut but currently reaches nothing.
  • Shaded when it has no boolean at all: then it is simply a body.

Older files

Sketches saved before parts existed keep working, but cannot be moved as parts until the file is updated. Run Update File (search for it with F3), or take the offer the Sketcher panel makes when the file was saved by an older version: a sketch drawn on a body joins that body's part, and one that has been made solid roots a part of its own. It is never done automatically on file open, since it restructures the file.

Collections

Collections are created and maintained for you, one per part and one per assembly, and anything belonging to no part sits at the scene level. Never exclude one from the view layer: excluding stops evaluation, which drops the sketch fill. Hide objects instead.