Pracovní plocha Skicář

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Úvod

Pracovní plocha Skicář je používána pro vytváření 2D konstrukcí určených pro použití v Pracovní ploše Návrh dílu a dalších pracovních plochách. Obecně jsou 2D konstrukce zamýšleny jako startovní bod pro většinu CAD modelů - jednoduchý 2D náčrt může být 'vysunut' do 3D tvaru, dále mohou být 2D náčrty použity k vytváření kapes v povrchu objektu a náčrty mohou být využity pro definování 'desek' (vysunutí) na povrchu 3D objektů. Spolu s logickými operacemi, náčrt vytváří jádro generativního návrhu dílu tělesa.

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.

Samotná pracovní plocha Skicář obsahuje vazby - umožňující 2D tvarům mít vazby pro přesné definice konstrukcí. A kalkulátor vazeb který počítá rozšíření vazeb 2D konstrukcí a umožňuje interaktivní zkoumání stupňů volnosti náčrtů.

Pro co není Skicář vhodný

Skicář není určen pro vytváření 2D výkresů. Protože náčrty jsou používány pro generování těles, jsou automaticky skrývány. Rozměry jsou viditelné pouze v editačním módu Náčrtu.

Základní plně vazbený náčrt‎.

Constraints

Co jsou vazby?

Vazby jsou použity k omezení stupňů volnosti objektu. Například přímka bez vazeb má 4 stupně volnosti: může se posunovat vodorovně nebo svisle, může být natahována a otáčena.

Použití vodorovné nebo svislé vazby nebo vazbu úhlu (relativně k jiné přímce nebo k některé z os) omezí její možnosti otáčení, takže jí zbudou jen tři stupně volnosti. Zavazbení jednoho bodu v relaci k počátku odebere další 2 stupně volnosti. A aplikace vazby rozměru odebere poslední stupeň volnosti. Přímka je potom považována za plně vazbenou.

Více objektů může být vazbeno mezi sebou vzájemně. Dvě přímky mohou být spojeny prostřednictvím jejich bodů pomocí vazby souhlasných bodů. Může být nastaven úhel mezi nimi nebo mohou být nastaveny kolmo k sobě. Přímka se může dotýkat oblouku nebo kružnice, atd.

Jsou dva druhy vazeb: konstrukční a rozměrové. Detailně jsou rozebrány v sekci 'Nástroje' dále.

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.

Sketcher_Edit_Constraint.png

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.

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 an 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 PohledAutoconstraints property of the sketch.

The following constraints are applied automatically:

Snapping

introduced in version 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 version 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 version 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 version 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).

Tools

Nástroje

Nástroje pracovní plochy Skicář jsou umístěny v menu Skicář, které se zobrazí když natáhnete pracovní plochu Skicář.

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 version 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

  • Edit sketch: Opens the Sketcher Dialog to edit an existing sketch.
  • Reorient sketch: Places a sketch on one of the main planes with an optional offset. It can also be used to detach a sketch.
  • Validate sketch: Can analyze and repair a sketch that is no longer editable or has invalid constraints, or add missing coincident constraints.
  • Mirror sketch: Mirrors sketches across their X axis, Y axis, or origin.

Sketcher Edit Mode toolbar

  • View section: Toggles a temporary section plane that hides any objects and parts of objects in front of the sketch plane.

Sketcher edit tools toolbar

Other

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

Sketcher geometries

These are tools for creating objects.

  • Create (poly)line:
  • Polyline: Creates a series of line and arc segments connected by their endpoints. The tool has several modes.
  • Create arc:
  • 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 version 1.0: Or by both endpoints of one of its axes and a point along the ellipse.
  • Create rectangle:
  • Create regular polygon:
  • Square: Creates a square. Idem.
  • Octagon: Creates an octagon. Idem.
  • Regular polygon: Creates a regular polygon. The number of sides can be specified.
  • Create slot:
  • Slot: Creates a slot.
  • Create B-spline:
  • Toggle construction geometry: Either toggles the geometry creation tools to/from construction mode, or toggles selected geometry to/from construction geometry.

Sketcher constraints

These are tools for creating constraints. Some constraints require the use of Helper constraints.

  • 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 version 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.
  • Vertical distance: Fixes the vertical 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.
  • Distance: Fixes the length of a line, the distance between two points, the perpendicular distance between a point and a line; or, introduced in version 0.21, the distance between the edges of two circles or arcs, or between the edge of a circle or arc and a line; or, introduced in version 1.0, the length of an arc.
  • Auto radius/diameter: Fixes the radius of arcs and B-spline weight circles, and the diameter of circles.
  • Radius: Fixes the radius of circles, arcs and B-spline weight 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.
  • Lock: Applies Horizontal distance and Vertical distance constraints to points. If a single point is selected the constraints reference the origin of the sketch. If two or more points are selected the constraints reference the last point in the selection.
  • Coincident: Creates a coincident constraint between points, or a concentric constraint.
  • Horizontal/vertical constraints:
  • Horizontal: Constrains lines or pairs of points to be horizontal.
  • Vertical: Constrains lines or pairs of points to be vertical.
  • Parallel: Constrains lines to be parallel.
  • Perpendicular: Constrains two lines to be perpendicular, or two edges, or an edge and an axis, to be perpendicular at their intersection. The constraint can also connect two edges, forcing them to be perpendicular at the joint.
  • Tangent or collinear: Constrains two edges, or an edge and an axis, to be tangent. The constraint can also connect two edges, forcing them to be tangent at the joint. If two lines are selected they are made collinear.
  • Equal: Constrains edges to have an equal length (lines) or curvature (other edges except B-splines).
  • Symmetric: Constrains two points to be symmetrical around a line or axis, or around a third point.
  • Block: Blocks edges in place with a single constraint. It is mainly intended for B-splines.
  • Refraction (Snell's law): Constrains two lines to follow the law of refraction of light as it penetrates through an interface.
  • Toggle constraints:
  • Toggle driving/reference constraint: Toggles the dimensional constraint creation tools between driving and reference mode, or toggles selected dimensional constraints between those modes.

Sketcher tools

  • Create fillet/chamfer:
  • Edit edge:
  • Trim: Trims an edge at the nearest intersections with other edges.
  • Split: Splits an edge while transferring most constraints.
  • Extend: Extends or shortens a line or an arc to an arbitrary location, or to a target edge or point.
  • External geometry: Projects edges and/or vertices belonging to objects outside the sketch onto the sketch plane.
  • Carbon copy: Copies all geometry and constraints from another sketch into the active sketch.
  • Symmetry: Creates mirrored copies of selected elements.

Sketcher B-spline tools

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

Sketcher visual

  • Show/hide B-spline information layer:

Obsolete tools

  • Clone: Clones a Sketcher element. Not available in version 1.0 and above.
  • Close shape: Creates a closed shape by applying coincident constraints to endpoints. Not available in version 0.21 and above.
  • Corner-preserving fillet: Creates a fillet between two non-parallel lines while preserving their corner point. Not available in version 1.0 and above.
  • Connect edges: Connect Sketcher elements by applying coincident constraints to endpoints. Not available in version 0.21 and above.
  • Copy: Copies a Sketcher element. Not available in version 1.0 and above.
  • Move: Moves the selected geometry taking as reference the last selected point. Not available in version 1.0 and above.
  • Rectangular array: Creates an array of selected Sketcher elements. Not available in version 1.0 and above.

Preferences

Best practices

Dobrá praxe

Každý uživatel CADu si časem vytvoří svůj vlastní způsob práce, ale je několik obecných principů, které je dobré následovat.

  • Je snadnější pracovat se sérií jednoduchých náčrtů než s jedním složitým. Například první náčrt může být vytvořen jako základ 3D tvarů (buď deska nebo obtáčení), zatímco druhý může obsahovat otvory nebo vyřezy (kapsy). Některé detaily mohou být vynechány s pozdější realizací na 3D tvaru. Pokud je na náčrtu mnoho zaoblení, můžete je vynechat a přidat je až na 3D tvaru.
  • Vždy vytvářejte uzavřený profil jinak náčrt nebude generovat těleso, ale místo toho skupinu otevřených ploch. Pokud chcete aby některé objekty nebyly zahrnuty při vytváření tělesa, změňte je na konstrukční prvky pomocí nástroje Konstrukční mód.
  • Použijte vlastnost autovazba pro omezení počtu vazeb, když je musíte přidávat ručně.
  •  Je obecné pravidlo, nejprve nastavit konstrukční vazby, potom délkové vazby a nakonec uzamknout náčrt. Ale pamatujte si: pravidla jsou k tomu aby se porušovala. Když máte problémy s manipulací s náčrtem, může se hodit nastavit vazby mezi několika objekty před kompletací profilu.
  • Pokud je to možné vystřeďte náčrt na počátek (0,0) s vazbou uzamčení. Není-li náčrt symetrický, umístěte jeden z jeho bodů do počátku nebo vyberte pěkné kulaté číslo pro uzamčenou vzdálenost. Ve verzi v0.12 nejsou implementovány externí vazby (vazbí náčrt k existující 3D konstrukci jako jsou hrany nebo jiné náčrty).

To znamená, že pro umístění následujících konstrukčních náčrtů na první náčrt budete potřebovat nastavit vzdálenost relativně k prvnímu náčrtu ručně. Vazba uzamčení na (25,75) od počátku je mnohem jednodušší pro zapamatování než (23.47,73.02).

  • Máte-li možnost vybrat si mezi vazbou Délky a vazbou Svislé nebo Vodorovné vzdálenosti, dejte přednost té druhé. Vazby Svislé nebo Vodorovné vzdálenosti jsou méně náročné na výpočty.

Tutorials

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.