Importing a STEP File
Use STEP file to drop a part somebody else designed into your document: a bearing, a motor, a connector you are building a bracket around. Deselect everything so the objects group appears in the toolbar, click STEP file, and pick the file. There is no settings dialog. The picker opens, and the moment you choose a file the part is in your scene with the move and rotate gizmo already on it.
The tool is on the right-click menu too, and it accepts .step and .stp.
You get one body, whatever was in the file
An assembly with forty parts in it arrives as one body. Kapy does not unpack a STEP into separate bodies, and there is no option to. That is deliberate: an inserted part is a thing you are designing around, not a document you are taking over.
The consequence to plan for is that you cannot hide, colour or delete one screw of an imported assembly. If you need the parts separately, import them separately, or split them in the CAD they came from.
The body is real geometry, not a stand-in. Its faces and edges can be picked, measured, used as sketch planes and used in booleans like any other.
Placing it
The gizmo is the only way to position an imported STEP. Drag the arrows to move, the rings to rotate. Look for X, Y and Z fields in the timeline popover and you will not find them: position and rotation are not repeated there.
The popover, which you get by clicking the import step in the timeline, holds three things:
| Control | What it does |
|---|---|
| File | Names the file that is embedded. Click it to pick a different one and replace the geometry in place |
| Scale | One uniform factor, minimum 0.001, applied about the part's own origin. There is no per-axis scale |
| Ghost placeholder | Turns the body into an inert reference. See below |
Scale, rotation and position are applied in that order, so a scaled part rotates and moves as a whole rather than drifting off.
Ghost placeholder
Switch Ghost placeholder on and the part is drawn semi-transparent and stops responding to the mouse entirely. You cannot select it, snap to it or cut with it. It is there to be looked at: the shape of the motor you are leaving room for, the volume the battery has to fit into.
Replacing the file
Clicking File in the popover swaps the embedded part for another one. It is the right move when a supplier ships a revision, and it is the fastest way to break the rest of your model.
Replacing changes the faces. Anything you built against the old part, a sketch on one of its faces, a fillet on one of its edges, a boolean that named a face, is pointing at geometry that no longer exists in that form, and those steps go red on the next rebuild. A revision that looks identical is no safer: what matters is the file, not the shape.
Keep imported parts at arm's length and the problem does not arise. Build your own geometry against your own sketches and planes, use the imported part to check the fit, and replace it freely. References That Survive an Edit covers the general habit.
Units
Kapy asks you nothing about units when it reads a STEP, and there is no unit control anywhere on the feature: not in the picker, not in the timeline popover, not in the document. There is nothing for you to get wrong and nothing for you to set.
So check the result instead of the settings. Measure a dimension you know before you build anything against an imported part: a hole the supplier lists at 8 mm should measure 8 mm on the body you just inserted. Two minutes with the measure tool is cheaper than a bracket you print twice.
If the size is wrong, Scale is the only lever there is, and it is one uniform factor. A part that needs stretching in one direction has to be dealt with elsewhere.
The STEP lives inside your document
The bytes of the file are stored in the document itself, not linked. Move the document, send it to somebody, put it inside a smart object: the part travels with it and nothing goes missing.
The bill for that is size. The whole document, imported STEP included, has a ceiling of roughly 36 MB, and a heavy assembly eats it quickly. A document that will not save after an import is a document that has grown past the ceiling; import a lighter version of the part.
Inserting the same file a second time costs almost nothing, because Kapy reads it once and reuses it for every copy in the session.
Importing a STEP without a document
Dropping a .step onto the file manager does something different: it creates a new design containing that part at the origin and nothing else. It does not add the part to whatever you had open. See Creating and Importing Files.
When it fails
Three messages, in the order you will meet them.
Could not read that file.
The file could not be read from disk at all, before any geometry was attempted. Try the file again, or copy it somewhere local first.
Could not read this STEP file — it may be corrupt or not a valid STEP/STP file
The reader rejected the contents. This is what a truncated download looks like, and what a file with a .step extension that is not a STEP looks like.
This STEP file contains no geometry to import
The file parsed and held nothing to build a body from. Assembly files that carry only structure and references, with the solids in other files nearby, land here. Export the part again from the source CAD as a single self-contained file with geometry in it.
See also
- Importing an STL or OBJ: the other import route, for triangle meshes
- Exporting Your Model: what leaves the document, ghosts included
- Creating and Importing Files: dropping a STEP into the file manager instead
- Working with Several Bodies: hiding, naming and colouring the bodies you now have