How to align groups of woodworking parts in Sawdust

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Multi-select parts to group them into rigid subassemblies, then use Mate faces to bring two assemblies into exact face-to-face contact.

When you join a tabletop to a base or attach a leg frame to a stretcher subassembly, you want the entire subassembly to move as one rigid unit while two specific board faces meet. Grouping each subassembly first lets Mate faces align the contact without disturbing the joints inside either group.

Before continuing, review How to preview a parametric assembly before adding it if you have not built a multi-part assembly yet.

1. Group each subassembly

Select the parts that belong to a subassembly (Shift-click in the 3D scene or select them in the Build rail) and click Group parts in the bottom selection bar so they move together. Arrange the two subassemblies roughly near each other if needed so you can see both mating surfaces clearly.

Three loose bench top boards selected beside a grouped bench base, with the selection bar showing 3 selected and a Group 3 parts button.

2. Select both groups and open Mate faces

Click any part of the subassembly that stays put, then Shift-click any part of the one that moves. Each click selects its whole group, and the first group you click is the reference. When the selection comes down to two sides, Mate faces appears in the selection bar. Click it.

Every part of the bench base and the bench top selected, with the selection bar showing 7 selected and a Mate faces button.

3. Pick the faces and where they meet

In the Mate panel, choose the reference face and the moving face. Then pick where the moving group sits flush on the reference (a corner, an edge or the center), fine-tune the offset if you need to, and set the spin if it has to turn.

The Mate panel with Reference face set to Top, Moving face set to Bottom, the center cell of Where it sits (flush) selected, the Spin row, and the Cancel and Mate buttons.

4. Check the preview and press Mate

The stage previews the result before anything is saved. When the faces meet the way you intended, press Mate. The whole moving group travels together, so the joints inside it stay intact, and the reference group does not move.

The live mate preview with the bench base and the bench top in two tints, the top centered on the base rail.
The bench after mating, with its three-board top sitting flat and centered on the base rail.

5. Verify the joint from a second angle

Always orbit to the back and side of the joint after committing a mate. A single camera angle can hide a flipped face normal, a corner-versus-center anchor mismatch, or an unintended overlap.

If you are building through Dusty or a connected MCP assistant, name the exact parts, faces, and edge anchors you want mated (for example, mating the bottom face of top_frame to the top face of leg_assembly) rather than asking the assistant to eyeball coordinates.

Continue with How to preview a parametric assembly before adding it and How to label woodworking parts in Sawdust.