Union and Intersect

Use Union to keep everything either of two bodies covers, and Intersect to keep only what both cover. Select at least two bodies, then press U to union or N to intersect.

Union

The result is one body with the overlap counted once. Where the two bodies shared a face, the seam is cleaned up rather than left as a line across a flat surface. The last step of a union tidies coplanar faces into one.

Union is not the only way to join. An extrude set to Add joins as it builds, and for a shape you are drawing anyway that is fewer steps. Use Union for two bodies that already exist and were modelled separately. Each one keeps its own history until you decide to merge, and that arrangement is easier to edit later.

Intersect

Intersect keeps only the shared volume. Two bodies that do not overlap produce nothing, and the feature says so rather than leaving you an empty body:

Intersection is empty (selected bodies do not overlap)

The classic use is a mould or a cut-down. Build the shape you want, build a volume that describes where it is allowed to exist, and intersect the two.

Keep tools

Keep tools is one switch, and it does less than its name suggests.

Keep tools spares the tools. It never spares the target. The first body you picked is consumed whatever you set, and it becomes the result. With the switch on, the others survive alongside it. With it off, they are consumed too.

A union with Keep tools on gives you the fused body and the second block, sitting inside it. Leave the switch on when you want that block back as a tool for another cut, and turn it off when you do not.

What happens to the bodies

The result takes the feature's name, so renaming the Union step in the timeline renames the body it produces. Bodies that were consumed keep their identity behind the scenes, so turning Keep tools back on brings them back rather than creating new ones.

If you need a consumed body again, edit the boolean and switch Keep tools on instead of modelling it a second time.

See also

• Subtract: removing one body from another
• Extrude and Cut: joining as you build instead
• Working with Several Bodies: when to keep bodies apart