External references: top-down design
A sketch of one part can stand on a face of another. The parts then share an external reference: the sketch follows the face wherever it goes.
This is how top-down design works: the housing comes first, and the bracket, the lid and the gasket take their sizes from it. Retyping those sizes by hand means keeping a second copy of one value and one day editing only one of them.
How to make one
- Step into the part you are building (double-click it in the tree).
- Turn on In context in the bar above: the neighbouring parts show as ghosts.
- Press Sketch (the pencil, key K) and click a face of the neighbouring part — as you would your own.
The sketch stands on that face, and the reference is recorded by itself. Everything built on the sketch follows the neighbour: move or edit the housing, and the bracket rebuilds.
How to see and break it
Select the part in the tree: the properties on the right list, under External references, the faces of the neighbours it stands on. The button with a cross beside a row is Break the link: the geometry freezes in place as a snapshot and stops following the neighbour. Do this when the part goes into production and must no longer change after the housing.
If it did not work
- The neighbours are not shown — In context is off.
- The sketch does not follow the neighbour — the link was broken: the row is gone from the part's External references. Build the sketch on the face again.
- Do not make rings: if the housing takes its sizes from the bracket and the bracket from the housing, the pair does not rebuild. Keep the design one way — from the leading part to the following one.