Subtract

Use Subtract to remove one body from another. Select the body to cut first, then the bodies doing the cutting, and press B.

The first body you pick is the one that gets cut

The popover shows the two roles as two fields. Target is the body being reduced; Tools is everything being removed from it. Your pick order fills them — the first body you selected is the target, the rest are tools — but it is not the only control any more.

Both rows are editable, so a wrong target costs one re-pick rather than all of them. Click Target, click the body you meant, and the body it replaces drops out of the tools list instead of sitting in both roles at once. While the Tools row is collecting, the target is greyed out in the viewport and cannot be clicked at all.

Keep tools, and why you would

Keep tools is off by default, so the cutting bodies are consumed along with the result. Turn it on and they survive, sitting where they were, ready to cut something else.

This is the setting that makes a tool body pay for itself. Model a hex socket, a cable channel or a clearance volume for a bearing once, then subtract it from every part that needs it with Keep tools on. Each subtraction is its own feature, so changing the tool's size updates every part that used it.

Keep tools says nothing about the target, because the target is not consumed. The result is written onto the body you cut: it keeps its name, its colour and its visibility, and a fillet or a shell further down the timeline is still aimed at the body it was always aimed at. A subtraction produces no body of its own — there is no Subtract 1 in a palette colour nobody chose — and renaming the body does not rename the step.

When the cut separates the body

A subtraction that takes a body apart hands back one body per piece. Cut a bar through and you get two bodies, not one body holding two halves that the Bodies window, the exporter and the slicer would each have to treat as a single part.

The biggest piece is the body you were editing: same name, same colour, same visibility. The others are named after it — Bracket (2), Bracket (3) — and take the next colours from the palette. They are ordinary bodies from there, so a rename or a colour you give one survives every rebuild, and deleting the subtraction deletes them along with the cut that made them. A crumb far smaller than anything a printer can make is not a piece: it is the hairline a boolean sheds where two faces were meant to be flush, and it is dropped without a word.

A subtraction drawn before this rule existed keeps its pieces together, because the steps after it in that document were aimed at the whole result.

Subtract, or a cut extrude?

Both remove material, and they suit different situations.

An extrude set to Subtract draws the shape it removes, from a sketch, at the moment it removes it. Use it for a hole, a slot, a pocket, anything whose shape only exists to be taken away.

A Subtract boolean removes a body that already exists. Use it when the shape is a thing in its own right: a part that has to fit, a component you imported, a clearance volume you will use again. If you would want to look at the shape on its own, model it as a body.

When it fails

A subtract with a missing input reports it plainly. A subtract whose bodies do not overlap is not an error at all. It removes nothing, and the result is the target unchanged. If a subtraction appears to have done nothing, check that the tool body is actually inside the target rather than beside it, then move it and rebuild.

See also

• Union and Intersect: the other two answers about two bodies
• Clearance Cut: a pocket a part can actually enter
• Cut and Push Face: cutting a shape you draw instead