Sketcher Workbench/sk

Úvod
Pracovný stôl Náčrtník sa vo FreeCADe používa na tvorbu 2D geometrie, ktorú následne využijete v na pracovnom stole Dizajn dielca,  pracovnom stole Arch a iných pracovných stoloch. Vo všeobecnosti sa za východiskový bod pre väčšinu CAD modelov považuje 2D náčrt, pretože ten dokážeme „vytiahnuť“ a vytvoriť tak 3D tvar; navyše je možné 2D náčrty okrem predtým vytvorených 3D tvarov použiť aj na vytvorenie ďalších prvkov, ako sú kapsy, ryhy alebo výlisky. Spolu s booleanovskými operáciami definovanými na pracovnom stole Diel tvorí Náčrtník základ konštruktívnej geometrie telies (CSG) - spôsobu tvorby telies. Okrem toho s operáciami pracovného stola Dizajn dielu tvorí Náčrtník tiež základ metodológie úpravy prvkov pri tvorbe telies.

Pracovný stôl Náčrtník obsahuje "väzby", vďaka ktorým dokážete pomocou presných geometrických definícií ako dĺžky, uhla a vzťahov (vodorovnosť, zvislosť, kolmosť atď.) určiť umiestnenie 2d tvarov. Riešiteľ väzieb vypočíta rozsah väzieb 2D geometrie a poskytuje interaktívne prehliadanie stupňov voľnosti náčrtu.



Základy používania väzieb náčrtu
Pre lepšie pochopenie fungovania Náčrtníka môže pomôcť porovnanie s "tradičným" spôsobom rysovania.

Tradičné rysovanie
Tradičné rysovanie v CAD programoch používa podobné techniky, ako technické výkresy. Jednotlivé pohľady sú kreslené manuálne a sú určené na tvorbu technických výkresov (modrotlač). Objekty sú kreslené presne pre zvolenú veľkosť alebo rozmer. Ak chcete nakresliť vodorovnú čiaru s dĺžkou 100 mm začínajúcu na (0,0), aktivujete nástroj čiara. Kliknete na obrazovku alebo zadáte súradnice (0,0) pre prvý bod, potom kliknete znovu alebo zadáte súradnice druhého bodu na (100,0). Alebo čiaru nakreslíte bez ohľadu na umiestnenie a presuniete ju neskôr. Po dokončení kreslenia geometrie jej priradíte rozmery.

Používanie väzieb náčrtu
"Náčrtník" sa od tohto postupu odlišuje. Objekty nemusia byť nakreslené úplne presne, pretože ich neskôr definujete priradenými väzbami. Môžete ich nakresliť voľne a pokiaľ sú bez väzieb, môžu byť upravované. V podstate "plávajú" na kresliacej ploche a môžete ich presúvať, naťahovať, otáčať, škálovať apod. To vám v procese návrhu poskytuje veľkú voľnosť.

Čo sú väzby?
Namiesto rozmerov sú väzby používané na obmedzenie stupňov voľnosti objektu. Napríklad čiara bez väzieb má 4 stupne voľnosti (skrátene SV, angl. DOF): môže byť posúvaná vodorovne alebo zvislo, môže byť natiahnutá a môže byť otočená.

Použitie vodorovnej alebo zvislej väzby alebo väzby uhla čiary (vzhľadom na inú čiaru alebo jednu z osí) obmedzí jej schopnosť otáčania, takže jej zostanú 3 stupne voľnosti. Zamknutie jedného z jej dvoch bodov vzhľadom na začiatok súradníc odstráni ďalšie 2 stupne voľnosti. A nakoniec použitie väzby rozmeru odstráni posledný stupeň voľnosti. Po týchto úkonoch je čiara považovaná za "plne zaväzbenú".

Multiple objects can be constrained between one another. Two lines can be joined through one of their points with the coincident point constraint. An angle can be set between them, or they can be set perpendicular. A line can be tangent to an arc or a circle, and so on. A complex Sketch with multiple objects will have a number of different solutions, and making it fully-constrained means that just one of these possible solutions has been reached based on the applied constraints.

There are two kinds of constraints: geometric and dimensional. They are detailed in the 'Tools' section below.

What the Sketcher is not good for
The Sketcher is not intended for producing 2D blueprints. Once sketches are used to generate a solid feature, they are automatically hidden. Constraints are only visible in Sketch edit mode.

If you only need to produce 2D views for print, and don't want to create 3D models, check out the Draft workbench. Unlike Sketcher elements, Draft objects don't use constraints; they are simple shapes defined at the moment of creation. Both Draft and Sketcher can be used for 2D geometry drawing, and 3D solid creation, although their preferred use is different; the Sketcher is normally used together with Part and PartDesign to create solids; Draft is normally used for simple planar drawings over a grid, as when drawing an architectural floor plan; in these situations Draft is mostly used together with the Arch Workbench. The tool Draft2Sketch converts a Draft object to a Sketch object, and vice versa; many tools that require a 2D element as input work with either type of object as an internal conversion is done automatically.

Sketching Workflow
A Sketch is always 2-dimensional (2D). To create a solid, a 2D Sketch of a single enclosed area is created and then either Padded or Revolved to add the 3rd dimension, creating a 3D solid from the 2D Sketch.

If a Sketch has segments that cross one another, places where a Point is not directly on a segment, or places where there are gaps between endpoints of adjacent segments, Pad or Revolve won't create a solid. Sometimes a Sketch which contains lines which cross one another will work for a simple operation such as Pad, but later operations such as Linear Pattern will fail. It is best to avoid crossing lines. The exception to this rule is that it doesn't apply to Construction (blue) Geometry.

Inside the enclosed area we can have smaller non-overlapping areas. These will become voids when the 3D solid is created.

Once a Sketch is fully constrained, the Sketch features will turn green; Construction Geometry will remain blue. It is usually "finished" at this point and suitable for use in creating a 3D solid. However, once the Sketch dialog is closed it may be worthwhile going to Part Workbench and running  to ensure there are no features in the Sketch which may cause later problems.

Tools
The Sketcher Workbench tools are all located in the Sketch menu that appears when you load the Sketcher Workbench.

General

 * [[Image:Sketcher_NewSketch.svg‎‎|32px]] New sketch: Creates‎ a new sketch on a selected face or plane. If no face is selected while this tool is executed the user is prompted to select a plane from a pop-up window.


 * [[Image:Sketcher_EditSketch.svg|32px]] Edit sketch: Edit the selected Sketch. This will open the Sketcher Dialog.


 * [[Image:Sketcher_LeaveSketch.svg|32px]] Leave sketch: Leave the Sketch editing mode.


 * [[Image:Sketcher_ViewSketch.svg|32px]] View sketch: Sets the model view perpendicular to the sketch plane.


 * [[Image:Sketcher_ViewSection.svg|32px]] View section: Creates a section plane that temporarily hides any matter in front of the sketch plane.


 * [[Image:Sketcher_MapSketch.svg|32px]] Map sketch to face: Maps a sketch to the previously selected face of a solid.


 * Sketcher_ReorientSketch.svg Reorient sketch: Allows you to attach the sketch to one of the main planes.


 * Sketcher_ValidateSketch.svg Validate sketch: Verify the tolerance of different points and adjust them.


 * [[Image:Sketcher_MergeSketches.svg|32px]] Merge sketches: Merge two or more sketches.


 * [[Image:Sketcher_MirrorSketch.svg|32px]] Mirror sketch: Mirror a sketch along the x-axis, the y-axis or the origin.


 * Sketcher_StopOperation.svg Stop operation: When in edit mode, stop the current operation, whether that is drawing, setting constraints, etc.

Sketcher geometries
These are tools for creating objects.


 * [[Image:Sketcher_CreatePoint.svg|32px]] Point: Draws a point.


 * [[Image:Sketcher_CreateLine.svg|32px]] Line: Draws a line segment between 2 points. Lines are infinite regarding certain constraints.


 * [[Image:Sketcher_CompCreateArc.png|48px]] Create an arc: This is an icon menu in the Sketcher toolbar that holds the following commands:


 * [[Image:Sketcher_CreateArc.svg|32px]] Arc: Draws an arc segment from center, radius, start angle and end angle.


 * [[Image:Sketcher_Create3PointArc.svg|32px]] Arc by 3 points: Draws an arc segment from two endpoints and another point on the circumference.


 * [[Image:Sketcher_CompCreateCircle.png|48px]] Create a circle: This is an icon menu in the Sketcher toolbar that holds the following commands:


 * [[Image:Sketcher_CreateCircle.svg|32px]] Circle: Draws a circle from center and radius.


 * [[Image:Sketcher_Create3PointCircle.svg|32px]] Circle by 3 points: Draws a circle from three points on the circumference.


 * [[Image:Sketcher_CompCreateConic.png|48px]] Create a conic: The sketcher provides the following conical sections. Unlike B-splines they can be used with all sorts of constraints such as Tangent, Point On Object, or Perpendicular.
 * [[Image:Sketcher_CreateEllipseByCenter.svg|32px]] Ellipse by center: Draws an ellipse by center point, major radius point and minor radius point.
 * [[Image:Sketcher_CreateEllipseBy3Points.svg|32px]] Ellipse by 3 points: Draws an ellipse by major diameter (2 points) and minor radius point.
 * [[Image:Sketcher_CreateArcOfEllipse.svg|32px]] Arc of ellipse: Draws an arc of ellipse by center point, major radius point, starting point and ending point.
 * [[Image:Sketcher_CreateArcOfHyperbola.svg|32px]] Arc of hyperbola: Draws an arc of hyperbola.
 * [[Image:Sketcher_CreateArcOfParabola.svg|32px]] Arc of parabola: Draws an arc of parabola.


 * [[Image:Sketcher_CompCreateBSpline.png|48px]] Create a B-spline: This is an icon menu in the Sketcher toolbar that holds the following commands:
 * Sketcher_CreateBSpline.svg Create B-spline: Draws a B-spline curve by its control points.
 * Sketcher_CreatePeriodicBSpline.svg Create periodic B-spline: Draws a periodic (closed) B-spline curve by its control points.


 * [[Image:Sketcher_CreatePolyline.svg|32px]] Polyline (multiple-point line): Draws a line made of multiple line segments. Pressing the M key while drawing a Polyline toggles between the different polyline modes.


 * [[Image:Sketcher_CompCreateRectangles.png|48px]] Create rectangles: This is an icon menu in the Sketcher toolbar that holds the following commands:


 * [[Image:Sketcher_CreateRectangle.svg|32px]] Rectangle: Draws a rectangle from 2 opposite points.


 * [[Image:Sketcher_CreateRectangle_Center.svg|32px]] Centered Rectangle: Draws a rectangle from a central point and an edge point.


 * [[Image:Sketcher_CreateOblong.svg|32px]] Rounded Rectangle: Draws a rounded rectangle from 2 opposite points.


 * [[Image:Sketcher_CompCreateRegularPolygon.png|48px]] Create regular polygon: This is an icon menu in the Sketcher toolbar that holds the following commands:


 * [[Image:Sketcher_CreateTriangle.svg|32px]] Triangle: Draws a regular triangle inscribed in a construction geometry circle.


 * [[Image:Sketcher_CreateSquare.svg|32px]] Square: Draws a regular square inscribed in a construction geometry circle.


 * [[Image:Sketcher_CreatePentagon.svg|32px]] Pentagon: Draws a regular pentagon inscribed in a construction geometry circle.


 * [[Image:Sketcher_CreateHexagon.svg|32px]] Hexagon: Draws a regular hexagon inscribed in a construction geometry circle.


 * [[Image:Sketcher_CreateHeptagon.svg|32px]] Heptagon: Draws a regular heptagon inscribed in a construction geometry circle.


 * [[Image:Sketcher_CreateOctagon.svg|32px]] Octagon: Draws a regular octagon inscribed in a construction geometry circle.


 * [[Image:Sketcher_CreateRegularPolygon.svg|32px]] Create Regular Polygon : Draws a regular polygon by selecting the number of sides and picking two points: the center and one corner.


 * [[Image:Sketcher_CreateSlot.svg|32px]] Slot: Draws an oval by selecting the center of one semicircle and an endpoint of the other semicircle.


 * [[Image:Sketcher_CreateFillet.svg|32px]] Fillet: Makes a fillet between two lines joined at one point. Select both lines or click on the corner point, then activate the tool.


 * [[Image:Sketcher_Trimming.svg|32px]] Trimming: Trims a line, circle or arc with respect to the clicked point.


 * Sketcher_Extend.svg Extend: Extends a line or an arc to a boundary line, arc, ellipse, arc of ellipse or a point in space.


 * [[Image:Sketcher_Split.svg|32px]] Split: Splits a line or an arc into two, converts a circle into an arc while keeping most of the constraints.


 * [[Image:Sketcher_External.svg|32px]] External Geometry: Creates an edge linked to external geometry.


 * Sketcher_CarbonCopy.svg CarbonCopy: Copies the geometry of another sketch.


 * Sketcher_ToggleConstruction.svg Construction Mode: Toggles sketch geometry from/to construction mode. Construction geometry is shown in blue and is discarded outside of Sketch editing mode.

Sketcher constraints
Constraints are used to define lengths, set rules between sketch elements, and to lock the sketch along the vertical and horizontal axes. Some constraints require use of Helper constraints.

Geometric constraints
These constraints are not associated with numeric data.


 * Sketcher_ConstrainCoincident.svg Coincident: Affixes a point onto (coincident with) one or more other points.


 * Sketcher_ConstrainPointOnObject.svg Point On Object: Affixes a point onto another object such as a line, arc, or axis.


 * Sketcher_ConstrainVertical.svg Vertical: Constrains the selected lines or polyline elements to a true vertical orientation. More than one object can be selected before applying this constraint.


 * Sketcher_ConstrainHorizontal.svg Horizontal: Constrains the selected lines or polyline elements to a true horizontal orientation. More than one object can be selected before applying this constraint.


 * Sketcher_ConstrainParallel.svg Parallel: Constrains two or more lines parallel to one another.


 * Sketcher_ConstrainPerpendicular.svg Perpendicular: Constrains two lines perpendicular to one another, or constrains a line perpendicular to an arc endpoint.


 * Sketcher_ConstrainTangent.svg Tangent: Creates a tangent constraint between two selected entities, or a co-linear constraint between two line segments. A line segment does not have to lie directly on an arc or circle to be constrained tangent to that arc or circle.


 * Sketcher_ConstrainEqual.svg Equal: Constrains two selected entities equal to one another. If used on circles or arcs their radii will be set equal.


 * Sketcher_ConstrainSymmetric.svg Symmetric: Constrains two points symmetrically about a line, or constrains the first two selected points symmetrically about a third selected point.


 * [[Image:Sketcher_ConstrainBlock.svg|32px]] Block: it blocks an edge from moving, that is, it prevents its vertices from changing their current positions. It should be particularly useful to fix the position of B-Splines. See the Block Constraint forum topic.

Dimensional constraints
These are constraints associated with numeric data, for which you can use the expressions. The data may be taken from a spreadsheet.


 * Sketcher_ConstrainLock.svg Lock: Constrains the selected item by setting vertical and horizontal distances relative to the origin, thereby locking the location of that item. These constraint distances can be edited later.


 * Sketcher_ConstrainDistanceX.svg Horizontal distance: Fixes the horizontal distance between two points or line endpoints. If only one item is selected, the distance is set to the origin.


 * Sketcher_ConstrainDistanceY.svg Vertical distance: Fixes the vertical distance between 2 points or line endpoints. If only one item is selected, the distance is set to the origin.


 * Sketcher_ConstrainDistance.svg Distance: Defines the distance of a selected line by constraining its length, or defines the distance between two points by constraining the distance between them.


 * Sketcher_ConstrainRadius.svg Radius: Defines the radius of a selected arc or circle by constraining the radius.
 * Sketcher_ConstrainDiameter.svg Diameter: Defines the diameter of a selected arc or circle by constraining the diameter.
 * Sketcher_ConstrainRadiam.svg Radiam: Automatically defines radius/diameter of a selected arc or circle (weight for a B-spline pole, diameter for a complete circle, radius for an arc)
 * Sketcher_ConstrainAngle.svg Angle: Defines the internal angle between two selected lines.

Special constraints

 * Sketcher_ConstrainSnellsLaw.svg Snell's Law: Constrains two lines to obey a refraction law to simulate the light going through an interface.


 * Sketcher_ConstrainInternalAlignment.svg Internal alignment: Aligns selected elements to selected shape (e.g. a line to become major axis of an ellipse).

Constraint tools
The following tools can be used the change the effect of constraints:


 * Sketcher_ToggleDrivingConstraint.svg Toggle driving/reference constraint: Toggles the toolbar or the selected constraints to/from reference mode.


 * Sketcher_ToggleActiveConstraint.svg Activate/Deactivate constraint: Enable or disable an already placed constraint.

Sketcher tools

 * Sketcher_SelectElementsWithDoFs.svg Select solver DOFs: Highlights in green the geometry with degrees of freedom (DOFs), i.e. not fully constrained.


 * Sketcher_CloseShape.svg Close Shape: Creates a closed shape by applying coincident constraints to endpoints.


 * Sketcher_ConnectLines.svg Connect Edges: Connect sketcher elements by applying coincident constraints to endpoints.


 * Sketcher_SelectConstraints.svg Select Constraints: Selects the constraints of a sketcher element.


 * Sketcher_SelectElementsAssociatedWithConstraints.svg Select Elements Associated with constraints: Select sketcher elements associated with constraints.


 * Sketcher_SelectRedundantConstraints.svg Select Redundant Constraints: Selects redundant constraints of a sketch.


 * Sketcher_SelectConflictingConstraints.svg Select Conflicting Constraints: Selects conflicting constraints of a sketch.


 * Sketcher_RestoreInternalAlignmentGeometry.svg Show/Hide internal geometry: Recreates missing/deletes unneeded internal geometry of a selected ellipse, arc of ellipse/hyperbola/parabola or B-spline.


 * Sketcher_SelectOrigin.svg Select Origin: Selects the origin of a sketch.


 * Sketcher_SelectVerticalAxis.svg Select Vertical Axis: Selects the vertical axis of a sketch.


 * Sketcher_SelectHorizontalAxis.svg Select Horizontal Axis: Selects the horizontal axis of a sketch.


 * Sketcher_Symmetry.svg Symmetry: Copies a sketcher element symmetrical to a chosen line.


 * Sketcher_Clone.svg Clone: Clones a sketcher element.


 * Sketcher_Copy.svg Copy: Copies a sketcher element.


 * Sketcher_Move.svg Move: Moves the selected geometry taking as reference the last selected point.


 * Sketcher_RectangularArray.svg Rectangular Array: Creates an array of selected sketcher elements.


 * Sketcher_RemoveAxesAlignment.svg Remove Axes Alignment: Remove axes alignment while trying to preserve the constraint relationship of the selection.


 * Sketcher_DeleteAllGeometry.svg Delete All Geometry: Deletes all geometry from the sketch.


 * Sketcher_DeleteAllConstraints.svg Delete All Constraints: Deletes all constraints from the sketch.

Sketcher B-spline tools

 * Sketcher_BSplineDegree.svg Show/hide B-spline degree


 * Sketcher_BSplinePolygon.svg Show/hide B-spline control polygon


 * Sketcher_BSplineComb.svg Show/hide B-spline curvature comb


 * Sketcher_BSplineKnotMultiplicity.svg Show/hide B-spline knot multiplicity


 * Sketcher_BSplinePoleWeight.svg Show/hide B-spline control point weight,


 * Sketcher_BSplineApproximate.svg Convert geometry to B-spline


 * Sketcher_BSplineIncreaseDegree.svg Increase B-spline degree


 * Sketcher_BSplineDecreaseDegree.svg Decrease B-spline degree,


 * Sketcher_BSplineIncreaseKnotMultiplicity.svg Increase knot multiplicity


 * Sketcher_BSplineDecreaseKnotMultiplicity.svg Decrease knot multiplicity

Sketcher virtual space

 * Sketcher_SwitchVirtualSpace.svg Switch Virtual Space: Allows you to hide all constraints of a sketch and make them visible again.

Preferences

 * [[Image:Preferences-general.svg|32px]] Preferences: Preferences for the Sketcher workbench.

Best Practices
Every CAD user develops his own way of working over time, but there are some useful general principles to follow.


 * A series of simple sketches is easier to manage than a single complex one. For example, a first sketch can be created for the base 3D feature (either a pad or a revolve), while a second one can contain holes or cutouts (pockets). Some details can be left out, to be realized later on as 3D features. You can choose to avoid fillets in your sketch if there are too many, and add them as a 3D feature.
 * Always create a closed profile, or your sketch won't produce a solid, but rather a set of open faces. If you don't want some of the objects to be included in the solid creation, turn them to construction elements with the Construction Mode tool.
 * Use the auto constraints feature to limit the number of constraints you'll have to add manually.
 * As a general rule, apply geometric constraints first, then dimensional constraints, and lock your sketch last. But remember: rules are made to be broken. If you're having trouble manipulating your sketch, it may be useful to constrain a few objects first before completing your profile.
 * If possible, center your sketch to the origin (0,0) with the lock constraint. If your sketch is not symmetric, locate one of its points to the origin, or choose nice round numbers for the lock distances. In v0.12, external constraints (constraining the sketch to existing 3D geometry like edges or to other sketches) are not implemented. This means that to locate following sketches geometry to your first sketch, you'll need to set distances relative to your first sketch manually. A lock constraint of (25,75) from the origin is more easily remembered than (23.47,73.02).
 * If you have the possibility to choose between the Length constraint and the Horizontal or Vertical Distance constraints, prefer the latter. Horizontal and Vertical Distance constraints are computationally cheaper.
 * In general, the best constraints to use are: Horizontal and Vertical Constraints; Horizontal and Vertical Length Constraints; Point-to-Point Tangency. If possible, limit the use of these: the general Length Constraint; Edge-to-Edge Tangency; Fix Point Onto a Line Constraint; Symmetry Constraint.
 * If in doubt about the validity of a sketch once it is complete (features turn green), close the Sketcher dialog, switch to the [[Image:Workbench_Part.svg|24px]] Part Workbench and run.

Tutorials

 * Sketcher tutorial by chrisb. This is a 70-page long 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.