Symmetric Relation
The Symmetric relation makes two lines, circles or arcs mirror images of each other across a construction line, and keeps them that way as the sketch changes.
When to Use It
- Keep the two sides of a part balanced about its center line
- Hold two holes the same distance either side of an axis
- Make a design change one side and have the other follow
Step by Step
- Open a sketch and draw the pieces (see Lines, Circles and Rectangles). Sketching is part of modeling, which comes with the Pro plans.
- Click Select on the Sketch tab (or press S).
- Click the construction line, then click the two lines (or two circles, or two arcs) that should mirror each other. Pick exactly three pieces.
- Keep the pointer still for about half a second. A bar titled Add a relation to the N selected opens beside it, with one button for each relation that fits. Click Symmetric. Instead of waiting for the bar, you can right-click the selection and choose Symmetric under Make them, or click Symmetric under Add a relation in the Properties panel.
- A small green square marks the relation on the sketch, and a message says Symmetric added. It stays true as you move and resize; Edit, Constraints lists it. Ctrl+Z takes it back.
Options
| Setting | What it does |
|---|---|
| Picks | A construction line plus two pieces of the same kind: two lines, two circles or two arcs. If you pick more than one construction line, the first one is the mirror line. |
| Result | The second piece becomes the mirror image of the first across the construction line. A piece that is anchored (an origin, a part edge, a Fix) stays and the other moves. |
| Message | Symmetric added: [one piece] is now the mirror image of [the other] across [the line]. Ctrl+Z takes it back. |
| Listed as | Symmetric. |
| Also added by | Mirror Entities adds this relation to its copies when Keep originals is ticked. |
Tips
- If the construction line is parallel to both of the other two lines, the choice is Symmetric between lines instead (see Symmetric Between Lines Relation).
- To mirror two points about a line, see Symmetric Points Relation.
- Draw the construction line with Line, then Construction line (see Construction Geometry).
- All three must be pieces drawn in the sketch. A point or a part edge in the picks changes the choices.
If Something Goes Wrong
- "Symmetric cannot hold together with the relations already there. Nothing changed." Something already placed (another relation, a typed size or a Fix) fights this one. Delete the one in the way from the list under Edit (see Edit Menu) and try again.
- "Symmetric already holds through the relations you have, so nothing was added." The sketch already forces this, so nothing more is needed.
- The button is not in the bar. The bar only lists relations that fit what you picked. Check what is selected in the Selected list of the Properties panel. If the panel says None fits this selection. Pick another point, piece or part edge with it., change the picks.
- "Symmetric applied once: the relation solver could not load, so it will not be kept." The piece moved once but nothing was stored. Check your connection and add it again.
- The bar does not show Symmetric. You need exactly three pieces, one of them a construction line, and the other two the same kind (two lines, two circles or two arcs). Two open lines must have the same number of points.