# Micro Tutorial do Sketcher - Práticas de Restrição

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 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 → 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 Edit sketch.

## Crie um Esboço

2. Click on 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 Create polyline, then trace four lines in the general shape of a rectangle around the origin.

Unconstrained rectangular sketch.

- 3.2. Select one horizontal line, and press 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 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 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 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.

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

Geometrical horizontal and vertical constraints.

- 4.6. Select one horizontal line, and press 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 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 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 Vertical distance, then enter
`10 mm`

.

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

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

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 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.

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

**The tools:**New sketch, Edit sketch, Leave sketch, View sketch, View section, Map sketch to face, Reorient sketch, Validate sketch, Merge sketches, Mirror sketch

**Sketcher geometries:**Point, Line by 2 point,**Create an arc,**Arc, Arc by 3 Point,**Create a circle**, Circle, Circle by 3 Point,**Create a conic**, Ellipse by center, Ellipse by 3 points, Arc of ellipse, Arc of hyperbola, Arc of parabola,**Create a B-spline**, Create B-spline, Create periodic B-pline, Polyline (multiple-point line), Rectangle,**Create regular polygon**, Triangle, Square, Pentagon, Hexagon, Heptagon, Octagon, Create Regular Polygon, Slot, Fillet, Trimming, Extend, External Geometry, CarbonCopy, Construction Mode

**Sketcher constraints****Geometric constraints**Coincident, Point On Object, Vertical, Horizontal, Parallel, Perpendicular, Tangent, Equal Length, Symmetric, Constrain Block**Dimensional constraints**Lock, Horizontal Distance, Vertical Distance, Distance, Radius, Internal Angle, Snell's Law, Internal Alignment, Toggle reference/driving constraint,

**Sketcher tools**Select solver DOFs, Close Shape, Connect Edges, Select Constraints, Select Origin, Select Vertical Axis, Select Horizontal Axis, Select Redundant Constraints, Select Conflicting Constraints, Select Elements Associated with constraints, Show/Hide internal geometry, Symmetry, Clone, Copy, Move, Rectangular Array, Delete All Geometry, Delete All Constraints

**Sketcher B-spline tools**Show/Hide B-spline degree, Show/Hide B-spline control polygon, Show/Hide B-spline curvature comb, Show/Hide B-spline knot multiplicity, Convert Geometry to B-spline, Increase degree, Increase knot multiplicity, Decrease knot multiplicity

**Sketcher virtual space**Switch Virtual Space

**Installation:**Windows, Linux, Mac;**Getting started****Basics:**About FreeCAD, Workbenches, Preferences, Document structure, Interface Customization, Properties, Mouse Model; Tutorials**Workbenches**: Arch, Draft, FEM, Image, Inspection, Mesh, OpenSCAD, Part, PartDesign, Path, Plot, Points, Raytracing, Reverse Engineering, Robot, Ship, Sketcher, Spreadsheet, Start, Surface workbench, TechDraw, Test Framework, Web

**Scripting:**Introduction to Python, FreeCAD scripting tutorial, FreeCAD Scripting Basics, How to install macros, Gui Command, Units**Modules:**Builtin modules, Workbench creation, Installing more workbenches**Meshes:**Mesh Scripting, Mesh Module**Parts:**The Part Module, Topological data scripting, PythonOCC, Mesh to Part**Coin scenegraph:**The Coin/Inventor scenegraph, Pivy**Qt interface:**PySide, Using the FreeCAD GUI, Dialog creation**Parametric objects:**Scripted objects**Other:**Code snippets, Line drawing function, Embedding FreeCAD, FreeCAD vector math library, Power users hub, Python, Macros, FreeCAD Scripting Basics, Topological data scripting