Advanced Attachment OYX

From FreeCAD Documentation
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Time to complete
1 hour
FreeCAD version
0.19 or above
Example files
See also

The objects in initial position


This demonstration addresses the use of the OYX attachment mode to adjust the position of the origin of a sketch as described in Part:Attachment, it is not comprehensive, but hopefully will help users experiment.

The image above shows the geometry used in this demonstration.

The lower right frame shows the top view of the scene. Note the scene includes a sketch containing a square and text indicating the vertical (Y), horizontal (X) axes of the sketch. The lower left corner of the square is located at 0,0,0 of the sketch (the origin of the sketch).

The origin of the sketch and the global origin (designated by the red, green and blue axis cross) are the same. In the other frames of the image we can see that the square is at Z=0, so the sketch is in the XY plane.

There are two other sketches which include geometry that will be used to re-position the sketch containing the square. One sketch contains an orange line that is oriented along the global Z axis in the XZ plane. The other sketch contains a yellow line in the XY plane.


Attachment mode Align O-Y-X is defined as follows in Part:Attachment: Matches object's origin with first referenced vertex and aligns its vertical and horizontal plane axes toward vertex/along line.. It also notes there are several reference combinations.

Reference combinations
Vertex, Vertex, Vertex
Vertex, Vertex, Edge
Vertex, Edge, Vertex
Vertex, Edge, Edge
Vertex, Vertex
Vertex, Edge

Lets start with Vertex, Vertex, Vertex.

If we match the definition to the reference:

The first vertex selected will position the origin of the sketch to the selected vertex.

The second vertex selected will align the vertical axis of the sketch (in the demo setup this axis is indicated with Y).

So, if we select the upper left/upper vertex of the yellow edge (as seen in the larger right frame) and the lower/right vertex of the yellow edge the sketch is positioned like this:

The Align O-Y-X is selected in the Attachment dialogue.
The sketch origin is now at the upper left/upper vertex of the yellow line.
The Y axis of the sketch is now aligned with the yellow line.
The Z axis of the sketch is perpendicular to the yellow line.

Now if we add a third reference by selecting the upper vertex of the orange edge the scene changes to:

Now the X axis of the sketch is aligned in the direction of the selected vertex of the orange edge.