Micro Tutorial do Sketcher - Práticas de Restrição

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This page is a translated version of the page Sketcher Micro Tutorial - Constraint Practices and the translation is 40% complete.
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Freecad.svg Tutorial
Topic
Sketcher
Level
Iniciante
Time to complete
30 minutos
Authors
Mark Stephen (Quick61) e vocx
FreeCAD version
0.19
Example files
Sketcher Constraints practices

Introdução

Este tutorial foi originalmente escrito por Quick61, e reescrito e reilustrado por vocx.

Este tutorial foi composto para ajudar o novo usuário a se familiarizar com as melhores práticas de restrição de esboço no fluxo de trabalho da Workbench Sketcher.svg Sketcher Workbench.

Existe uma regra geral para as restrições: quanto menor a quantidade de restrições de dados (cotas ou dimensões), melhor.

É preferível usar uma restrição geométrica em vez de uma dimensional, se possível. Isso tem a ver com o funcionamento interno do solucionador de restrições do Sketcher.

Configuração

1. Abra o FreeCAD, crie um novo documento em branco com Arquivo → Std New.svg Novo.

1.1. Switch to the Sketcher Workbench from the workbench selector, or the menu View → Workbench → Sketcher.

Some actions to remember:

  • Press the right mouse button, or press Esc in the keyboard once, to deselect the active tool in edit mode.
  • To exit the sketch edit mode, press the Close button in the task panel, or press Esc 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 Sketcher EditSketch.svg Edit sketch.

Crie um Esboço

2. Click on Sketcher NewSketch.svg New sketch.

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 OK to start constructing the sketch.

Note: in the task panel expand the Edit controls section, and make sure the Auto constraints option is disabled. Also turn off the grid snap, and hide the grid.

Primeira Abordagem: Restrições de Referência

3. We will draw a fully constrained square, centered at the origin.

3.1. Click on Sketcher CreatePolyline.svg Create polyline, then trace four lines in the general shape of a rectangle around the origin.

01a Sk02 Sketcher Rectangle unconstrained.png

Unconstrained rectangular sketch.

3.2. Select one horizontal line, and press Constraint HorizontalDistance.svg Horizontal distance, then enter 20 mm.
3.3. Select the other horizontal line, and repeat the constraint with the same distance.
3.4. Select one vertical line, and press Constraint VerticalDistance.svg Vertical distance, then enter 20 mm.
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 Constraint HorizontalDistance.svg Horizontal distance, then enter 10 mm.
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 Constraint VerticalDistance.svg Vertical distance, then enter 10 mm.
3.9. Select the top corner point (b) again, and the origin of the sketch, and repeat the vertical constraint with the same distance.

01b Sk02 Sketcher Rectangle constrained lengths 1.png 01c Sk02 Sketcher Rectangle constrained lengths 2.png

Left: datum constraints for the sides. Right: additional datum constraints for the interior distances.

Looking at the Constraints 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.

Uma Maneira Melhor: Referência e Restrições Geométricas

4. We will draw the same square fully constrained, and centered at the origin. When you create the new sketch, make sure the Auto constraints option is disabled.

4.1. Click on Sketcher CreatePolyline.svg Create polyline, then trace four lines in the general shape of a rectangle around the origin.
4.2. Select one horizontal line, and press Constraint Horizontal.svg Horizontal.
4.3. Select the other horizontal line, and repeat the constraint.
4.4. Select one vertical line, and press Constraint Vertical.svg Vertical.
4.5. Select the other vertical line, and repeat the constraint.

02a Sk02 Sketcher Rectangle constrained horizontal-vertical.png

Geometrical horizontal and vertical constraints.

4.6. Select one horizontal line, and press Constraint HorizontalDistance.svg Horizontal distance, then enter 20 mm. We see that the other horizontal line changes size at the same time.
4.7. Select one vertical line, and press Constraint VerticalDistance.svg Vertical distance, then enter 20 mm. 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 Constraint HorizontalDistance.svg Horizontal distance, then enter 10 mm.
4.9. Select the top corner point (b) above the previous corner point (a), and the origin of the sketch, and press Constraint VerticalDistance.svg Vertical distance, then enter 10 mm.

02b Sk02 Sketcher Rectangle constrained lengths 1.png 02c Sk02 Sketcher Rectangle constrained lengths 2.png

Left: datum constraints for only two sides. Right: additional datum constraints for only two interior distances.

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.

Esquema Ótimo: Principalmente Restrições Geométricas

5. We will draw the same square fully constrained, and centered at the origin. When you create the new sketch, make sure the Auto constraints option is disabled.

5.1. Click on Sketcher CreatePolyline.svg Create polyline, then trace four lines in the general shape of a rectangle around the origin.
5.2. Select one horizontal line, and press Constraint Horizontal.svg Horizontal.
5.3. Select the other horizontal line, and repeat the constraint.
5.4. Select one vertical line, and press Constraint Vertical.svg Vertical.
5.5. Select the other vertical line, and repeat the constraint.

03a Sk02 Sketcher Rectangle constrained horizontal-vertical.png

Geometrical horizontal and vertical constraints.

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 Constraint Symmetric.svg Symmetric. 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 Constraint EqualLength.svg Equal length. Notice that due to the symmetry of the corner points, all sides are now of the same size.

03b Sk02 Sketcher Rectangle constrained symmetric.png 03c Sk02 Sketcher Rectangle constrained equal length.png

Left: symmetric constraint for only two corner points. Right: additional equal length distances for only two adjacent sides.

5.8. Select one horizontal line, and press Constraint HorizontalDistance.svg Horizontal distance, then enter 20 mm. Due to the symmetric and length equality constraints previously added, we see that all sides become equal at the same time.

03d Sk02 Sketcher Rectangle constrained length.png

All geometric constraints applied, and a single datum constraint for a side.

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

Recursos Adicionais