Sketcher Micro Tutorial - Constraint Practices/de

Einführung
Dieses Tutorial wurde ursprünglich von Quick61 geschrieben, und es wurde von vocx neu geschrieben und neu illustriert.

Dieses Tutorium ist so gestaltet um dem neuen Anwender zu helfen, sich mit den bewährten Verfahren zur Beschränkung einer Skizze im Arbeitsablauf des Skizzierer Arbeitsbereichs vertraut zu machen.

Es gibt eine allgemeine Regel mit Beschränkungen: je weniger (Dimensionen), desto besser.

It is preferable to use a in place of a dimensional one if possible. This has to do with the internal workings of the Sketcher's constraint solver.

Einrichtung
1. Open FreeCAD, create a new empty document with.
 * 1.1. Switch to the Sketcher Workbench from the workbench selector, or the menu.

Some actions to remember:
 * Press the right mouse button, or press in the keyboard once, to deselect the active tool in edit mode.
 * To exit the sketch edit mode, press the button in the task panel, or press  twice in the keyboard.
 * To enter again edit mode, double click on the sketch in the tree view, or select it, and then click on.

Erstellen einer Skizze
2. Click on.
 * 2.1. Choose the sketch orientation, that is, one of the base XY, XZ, or YZ planes. We will use the default plane and options.
 * 2.2. Click to start constructing the sketch.

in the task panel expand the section, and make sure the  option is disabled. Also turn off the grid snap, and hide the grid.

Erster Näherung: Bezugsbeschränkungen
3. We will draw a fully constrained square, centered at the origin.
 * 3.1. Click on, then trace four lines in the general shape of a rectangle around the origin.




 * 3.2. Select one horizontal line, and press, then enter.
 * 3.3. Select the other horizontal line, and repeat the constraint with the same distance.
 * 3.4. Select one vertical line, and press, then enter.
 * 3.5. Select the other vertical line, and repeat the constraint with the same distance.
 * 3.6. Select one bottom corner point (a), and the origin of the sketch, and press, then enter.
 * 3.7. Select the top corner point (b) above the previous corner point (a), and the origin of the sketch, and repeat the horizontal constraint with the same distance.
 * 3.8. Select the other bottom corner point (c), and the origin of the sketch, and press, then enter.
 * 3.9. Select the top corner point (b) again, and the origin of the sketch, and repeat the vertical constraint with the same distance.



Looking at the section in the task panel, we see that the constraints are too many; they also clutter the view of the sketch. These constraints are also computationally intensive for the solver; while this is not an issue with a simple shape, it can become one with more complex shapes.

Ein besserer Weg: Bezugs und geometrische Beschränkungen
4. We will draw the same square fully constrained, and centered at the origin. When you create the new sketch, make sure the option is disabled.
 * 4.1. Click on, then trace four lines in the general shape of a rectangle around the origin.
 * 4.2. Select one horizontal line, and press.
 * 4.3. Select the other horizontal line, and repeat the constraint.
 * 4.4. Select one vertical line, and press.
 * 4.5. Select the other vertical line, and repeat the constraint.




 * 4.6. Select one horizontal line, and press, then enter . We see that the other horizontal line changes size at the same time.
 * 4.7. Select one vertical line, and press, then enter . We see that the other vertical line changes size at the same time.
 * 4.8. Select one bottom corner point (a), and the origin of the sketch, and press, then enter.
 * 4.9. Select the top corner point (b) above the previous corner point (a), and the origin of the sketch, and press, then enter.



This is a better constrained sketch than the first one. The horizontal and vertical geometric constraints allow us to use fewer datum constraints, so our sketch looks less cluttered.

Optimales Schema: meist geometrische Beschränkungen
5. We will draw the same square fully constrained, and centered at the origin. When you create the new sketch, make sure the option is disabled.
 * 5.1. Click on, then trace four lines in the general shape of a rectangle around the origin.
 * 5.2. Select one horizontal line, and press.
 * 5.3. Select the other horizontal line, and repeat the constraint.
 * 5.4. Select one vertical line, and press.
 * 5.5. Select the other vertical line, and repeat the constraint.




 * 5.6. Select one bottom corner point (a), then the top corner point that is diagonally opposite, and then the origin of the sketch; then press . The two selected points will be equidistant from the origin.
 * 5.7. Select two adjacent sides of the rectangle (connected at one corner), and press . Notice that due to the symmetry of the corner points, all sides are now of the same size.




 * 5.8. Select one horizontal line, and press, then enter . Due to the symmetric and length equality constraints previously added, we see that all sides become equal at the same time.



This is the best way to constrain this sketch, as we only used one datum (dimensional) constraint.

Zusätzliche Quellen

 * Grundlegendes Skizzierer Tutorium
 * Skizzierer Referenz
 * Skizzierer Tutorium