Sketcher Workbench/zh-cn

Together with boolean operations defined in the Part Workbench, the Sketcher Workbench, or "The Sketcher" for short, forms the basis of the constructive solid geometry (CSG) method of building solids. Together with PartDesign Workbench operations, it also forms the basis of the feature editing methodology of creating solids. But many other workbenches use sketches as well.

Constraints

Edit constraints

When a driving dimensional constraint is created, and if the Ask for value after creating a dimensional constraint preference is selected (default), a dialog opens to edit its value.

You can enter a numerical value or an expression, and it is possible to name the constraint to facilitate its use in other expressions. You can also check the Reference checkbox to switch the constrain to reference mode.

To edit the value of an existing dimensional constraint do one of the following:

• Double-click the constraint value in the 3D view.
• Double-click the constraint in the Sketcher Dialog.
• Right-click the constraint in the Sketcher Dialog and select the Change value option from the context menu.

Reposition constraints

Dimensional constraints can be repositioned in the 3D view by dragging. Hold down the left mouse button over the constraint value and move the mouse. The symbols of geometric constraints are positioned automatically and cannot be moved.

Profile sketches

To create a sketch that can be used as a profile for generating solids certain rules must be followed:

• The sketch must contain only closed contours. Gaps between endpoints, however small, are not allowed.
• Contours can be nested, to create voids, but should not self-intersect or intersect other contours.
• Contours cannot share edges with other contours. Duplicate edges must be avoided.
• T-connections, that is more than two edges sharing a common point, or a point touching an edge, are not allowed.

These rules do not apply to construction geometry (default color blue), which is not shown outside edit mode, or if the sketch is used for a different purpose. Depending on the workbench and the tool that will use the profile sketch, additional restrictions may apply.

Tools

Some tools are also available from the 3D view context menu while a sketch is in edit mode, or from the context menus of the Sketcher Dialog.

introduced in 0.21: If a sketch is in edit mode the Structure toolbar is hidden as none of its tools can then be used.

General

Sketcher toolbar

Sketcher Edit Mode toolbar

Sketcher edit tools toolbar

• Toggle grid: Toggles the grid in the sketch currently being edited. Settings can be changed in the related menu. introduced in 0.21

• Toggle snap: Toggles snapping in all sketches. Settings can be changed in the related menu. introduced in 0.21

• Configure rendering order: The rendering order of all sketches can be changed in the related menu. introduced in 0.21

Other

• Stop operation: Stops any currently running geometry or constraint creation tool.

• Create arc:

• Arc of ellipse: Creates an arc of ellipse.

• Arc of hyperbola: Creates an arc of hyperbola.

• Arc of parabola: Creates an arc of parabola.

• Create circle/ellipse:

• Ellipse by center: Creates an ellipse by its center, an endpoint of one of its axes, and a point along the ellipse. introduced in 1.0: Or by both endpoints of one of its axes and a point along the ellipse.

• Ellipse by 3 points: Creates an ellipse by the endpoints of one of its axes and a point along the ellipse. introduced in 1.0: This is the same tool as Ellipse by center but with a different initial mode.

• Create rectangle:

• Centered rectangle: Creates a centered rectangle. introduced in 1.0: This is the same tool as Rectangle but with a different initial mode.

• Rounded rectangle: Creates a rounded rectangle. Idem.

• Create regular polygon:

• Create slot:

• Arc slot: Creates an arc slot. introduced in 1.0

• Create B-spline:

• B-spline by control points: Creates a B-spline curve by control points. introduced in 1.0: Or by knot points.

• Periodic B-spline by control points: Creates a periodic (closed) B-spline curve by control points. introduced in 1.0: This is the same tool as B-spline by control points but with a different initial mode.

• B-spline by knots: Creates a B-spline curve by knot points. Idem.

• Periodic B-spline by knots: Creates a periodic (closed) B-spline curve by knot points. Idem.

• Dimensional constraints:

• Dimension: Is the context-sensitive constraint tool of the Sketcher Workbench. Based on the current selection, it offers appropriate dimensional constraints, but also geometric constraints. introduced in 1.0

• Horizontal distance: Fixes the horizontal distance between two points or the endpoints of a line. If a single point is pre-selected, the distance is relative to the origin of the sketch.

• Auto radius/diameter: Fixes the radius of arcs and B-spline weight circles, and the diameter of circles.

• Diameter: Fixes the diameter of circles and arcs.

• Angle: Fixes the angle between two edges, the angle of a line with the horizontal axis of the sketch, or the aperture angle of a circular arc.

• Coincident (unified): Creates a coincident constraint between points, fixes points on edges or axes, or creates a concentric constraint. It combines the Coincident and Point on object tools. introduced in 1.0

• Horizontal/vertical constraints:

• Horizontal/vertical: Constrains lines or pairs of points to be horizontal or vertical, whichever is closest to the current alignment. It combines the Horizontal and Vertical tools. introduced in 1.0

• Block: Blocks edges in place with a single constraint. It is mainly intended for B-splines.

• Toggle constraints:

• Activate/deactivate constraint: Activates or deactivates selected constraints.

• Create fillet/chamfer:

• Chamfer: creates a chamfer between two non-parallel edges. This is the same tool as Fillet but with a different initial mode. introduced in 1.0

• Edit edge:

• Split: Splits an edge while transferring most constraints.

• External geometry:

• Create external projection geometry: Creates the projection edges of external geometry. introduced in 1.1

• Create external intersection geometry: Creates the intersection edges of external geometry with the sketch plane. introduced in 1.1

• Array transform: Moves or optionally creates copies of selected elements. introduced in 1.0

• Polar transform: Rotates or optionally creates rotated copies of selected elements. introduced in 1.0

• Scale transform: Scales or optionally creates scaled copies of selected elements. introduced in 1.0

• Offset geometry: Creates equidistant edges around selected edges. introduced in 1.0

• Symmetry: Creates mirrored copies of selected elements.

• Remove axes alignment: Removes the axes alignment of selected edges by replacing Horizontal and Vertical constraints with Parallel and Perpendicular constraints.

• Delete all geometry: Deletes all geometry and all constraints from the sketch.

• Delete all constraints: Deletes all constraints from the sketch.

• Copy in Sketcher: See Copy, cut and paste.

• Cut in Sketcher: See Copy, cut and paste.

• Paste in Sketcher: See Copy, cut and paste.

Sketcher B-spline tools

• Convert geometry to B-spline: Converts edges to B-splines.

• Increase B-spline degree: Increases the degree (order) of B-splines.

• Decrease B-spline degree: Decreases the degree (order) of B-splines.

• Increase knot multiplicity: Increases the multiplicity of a B-spline knot.

• Decrease knot multiplicity: Decreases the multiplicity of a B-spline knot.

• Insert knot: Inserts a knot into a B-spline or increases the multiplicity of an existing knot.

• Join curves: Creates a B-spline by joining two existing B-splines or other edges. introduced in 0.21

Sketcher visual

• Select unconstrained DoF: Selects the not fully constrained elements in the sketch.

• Show/hide circular helper for arcs: Shows or hides the circular helpers (underlying virtual circles) for arcs in all sketches. introduced in 1.0

• Show/hide B-spline information layer:

• Show/hide B-spline degree: Shows or hides the B-spline degree in all sketches.

• Show/hide B-spline control polygon: Shows or hides the B-spline control polygon in all sketches.

• Show/hide B-spline curvature comb: Shows or hides the B-spline curvature comb in all sketches.

• Show/hide B-spline knot multiplicity: Shows or hides the B-spline knot multiplicity in all sketches.

• Show/hide B-spline control point weight: Shows or hides the B-spline control point weight in all sketches.

• Show/hide internal geometry: Deletes the internal geometry of elements, or recreates missing internal geometry.

• Switch virtual space: (un)hides constraints or switches the visible virtual space.

Obsolete tools

• Clone: Clones a Sketcher element. Not available in 1.0 and above.

• Corner-preserving fillet: Creates a fillet between two non-parallel lines while preserving their corner point. Not available in 1.0 and above.

• Copy: Copies a Sketcher element. Not available in 1.0 and above.

• Move: Moves the selected geometry taking as reference the last selected point. Not available in 1.0 and above.

• Rectangular array: Creates an array of selected Sketcher elements. Not available in 1.0 and above.

Preferences

• Preferences: Preferences for the Sketcher Workbench.

Drawing aids

The Sketcher Workbench has several drawing aids and other features that can help when creating geometry and applying constraints.

Continue modes

There are two continue modes: Geometry creation "Continue Mode" and Constraint creation "Continue Mode". If these are checked (default) in the preferences, related tools will restart after finishing. To exit a continuous tool press Esc or the right mouse button. This must be repeated if a continuous geometry tool has already received input. You can also exit a continuous tool by starting another geometry or constraint creation tool. Note that pressing Esc if no tool is active will exit sketch edit mode. Uncheck the Esc can leave sketch edit mode preference if you often inadvertently press Esc too many times.

Auto constraints

In sketches that have Auto constraints checked (default) several constraints are applied automatically. The icon of a proposed automatic constraint is shown next to the cursor when it is placed correctly. Left-clicking will then apply that constraint. This is a per-sketch setting that can be changed in the Sketcher Dialog or by changing the 视图Autoconstraints property of the sketch.

The following constraints are applied automatically:

• Coincident
• Point on object
• Horizontal
• Vertical
• Tangent
• introduced in 1.0: Symmetric (line midpoint)

Snapping

introduced in 0.21

It is possible to snap to grid lines and grid intersection, to edges of geometry and midpoints of lines and arcs, and to certain angles. Please note that snapping does not produce constraints in and of itself. For example, only if Auto constraints is switched on will snapping to an edge produce a Point on object constraint. But just picking a point on the edge would then have the same result.

On-View-Parameters

introduced in 1.0

Depending on the selected option in the preferences only the dimensional On-View-Parameters or both the dimensional and the positional On-View-Parameters can be enabled. Positional parameters allow the input of exact coordinates, for example the center of a circle, or the start point of a line. Dimensional parameters allow the input of exact dimensions, for example the radius of a circle, or the length and angle of a line. On-View-Parameters are not available for all tools.

Determining the center point of a circle with the positional parameters enabled

Determining the radius of a circle with the dimensional parameters enabled

If values are entered and confirmed by pressing Enter or Tab, related constraints are added automatically. If two parameters are displayed at the same time, for example the X and Y coordinate of a point, it is possible to enter one value and pick a point to define the other. Depending on the object additional constraints may be required to fully constrain it. Constraints resulting from On-View-Parameters take precedence over those that may result from Auto constraints.

Arc created by entering all On-View-Parameters with resulting automatically created constraints

Coordinate display

If the Show coordinates beside cursor while editing preference is checked (default), the parameters of the current geometry tool (coordinates, radius, or length and angle) are displayed next to the cursor. This is deactivated while On-View-Parameters are shown.

Selection methods

While a sketch is in edit mode the following selection methods can be used:

3D view element selection

As elsewhere in FreeCAD, an element can be selected in the 3D view with a single left mouse click. But there is no need to hold down the Ctrl key when selecting multiple elements. Holding down that key is possible though and has the advantage that you can miss-click without losing the selection. Edges, points and constraints can be selected in this manner.

3D view box selection

Box selection in the 3D view works without using Std BoxSelection or Std BoxElementSelection:

1. Make sure that no tool is active.
2. Do one of the following:
   • Click in an empty area and drag a rectangle from left to right to select elements that lie completely inside the rectangle.
   • Click in an empty area and drag a rectangle from right to left to also select elements that touch or cross the rectangle.

You can box-select edges and points, constraints cannot be box-selected.

3D view connected geometry selection

introduced in 1.0

Double-clicking an edge in the 3D view will select all edges directly and indirectly connected with that edge via endpoints. There is no need for the edges to be connected with Coincident constraints, endpoints need only have the same coordinates.

Sketcher Dialog selection

Edges and points can also be selected from the Elements section of the Sketcher Dialog, and constraints from the Constraints section of that dialog.

Copy, cut and paste

introduced in 1.0

The standard keyboard shortcuts, Ctrl+C, Ctrl+X and Ctrl+V, can be used to copy, cut and paste selected Sketcher geometry including related constraints. But these tools are also available from the Sketch → Sketcher tools menu. They can be used within the same sketch but also between different sketches or separate instances of FreeCAD. Since the data is copied to the clipboard in the form of Python code, it can be used in other ways too (e.g. shared on the forum).

Best practices

Flipping

The phenomenon that a fully constrained sketch, usually after a major change to one of its dimensions, reaches an unintended new state is know as "flipping". In the example below, changing one dimension completely changes the shape of the sketch. Note that the sketch with the new shape is still fully constrained.

Original sketch (left), and the same sketch after increasing the 20mm value to 1000mm (right)

Methods to reduce flipping

Change dimensions in small increments

This is not always practical, but changing dimension values in smaller increments can work.

Use a different solver

The LevenbergMarquardt solver, which is not the default solver, is known to be less prone to flipping. See Sketcher Dialog for more information.

Use horizontal and vertical dimensions

Using horizontal and vertical dimensions instead of equal constraints can prevent flipping. Points constrained by these dimensions will not switch places. In the image above the added (orange) dimensional constraints are linked to the original dimensions via expressions.

Use angular dimensions

Using angular dimensions instead of horizontal and vertical constraints can also work. The angle between edges constrained by angular dimensions will not change. 180° will not become 0°, 90° will not become 270°, etc. In the image all horizontal and vertical constraints have been replaced, but just replacing two is already effective here.

• Sketcher Lecture by chrisb. This is a more than 80 page PDF document that serves as a detailed manual for the Sketcher. It explains the basics of Sketcher usage, and goes into a lot of detail about the creation of geometrical shapes, and each of the constraints.
• Basic Sketcher Tutorial for beginners
• Sketcher Micro Tutorial - Constraint Practices
• Sketcher requirement for a sketch Minimum requirement for a sketch and Complete determination of a sketch

Scripting

The Sketcher scripting page contains examples on how to create constraints from Python scripts.

Examples

For some ideas of what can be achieved with Sketcher tools, have a look at: Sketcher examples.