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はじめに

スケッチャーワークベンチはパートデザインワークベンチやその他のワークベンチで使用するための2次元形状を作成するために使われます。ほとんどのCADモデルでは2次元形状が開始点となることが普通です・・まず簡単な2次元スケッチを'押し出して'3次元形状を作り、その形状の表面に穴を開けるための2次元スケッチを追加したり、スケッチで'突起'（押し出し形状）を定義したりします。スケッチャーはブーリアン演算と並んで3次元形状デザイン作成の中核を成す機能なのです。

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.

スケッチャーワークベンチの特徴はなんといっても拘束です・・これによって2次元形状を厳密な幾何定義に従って拘束することが可能です。また拘束用ソルバーによって2次元形状の拘束範囲を計算したり、スケッチの自由度を対話的に検査したりすることが可能です。

スケッチャーに向かないもの

スケッチャーは2次元図面を作成するためのものではありません。ソリッド形状を作成するとスケッチは自動的に非表示になります。寸法はスケッチ編集モード時のみ表示されます。

A fully constrained sketch

Constraints

拘束とは何なのか？

拘束は物体の自由度を制限するために使用されます。例えばラインは拘束がない場合は4つの自由度を持ちます。つまり水平方向、垂直方向への移動と拡大縮小と回転が可能です。

水平拘束、垂直拘束、あるいは（他のラインか座標軸の一つに対する）角度拘束を適用すると回転が制限され自由度は3つに減ります。片方の短点を原点に対してロックすることでさらに2つの自由度が減ります。最後にサイズ拘束を適用すれば最後の自由度が無くなります。こうしてラインは完全拘束状態になります。

複数のオブジェクトがある場合は相互に拘束が可能です。二本のラインがあった場合、点一致拘束を使用することでそれぞれの端点をつなぎ合わせることができます。また二本のラインの間の角度を設定したり、二本のラインが垂直になるよう設定することも可能です。ラインに対しては円弧や円の接線となるように拘束することもできます。

拘束には二種類あります。幾何拘束と寸法拘束です。これらについては下の'ツール'セクションで詳しく説明します。

Driving vs. reference constraints

Edit constraints

When a driving 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

Constraints can be repositioned in the 3D view by dragging. Hold down the left mouse button over the constraint value and move the mouse.

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 should 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 when hovering the cursor properly (their symbols are displayed next to the cursor before applying). This is a per-sketch setting that can be changed in the Sketcher Dialog or by changing the ビューAutoconstraints property of the sketch. The following constraints are applied automatically:

Coincident
Point on object
Horizontal
Vertical
Tangent
introduced in version 0.22: Symmetric (line midpoint)

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 0.22

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

No need for Ctrl, but... Select in Sketcher Dialog...

Box selection

Connected geometry selection

Copy, cut and paste

introduced in version 0.22

The standard keyboard shortcuts can be used to copy, Ctrl+C, cut, Ctrl+X, and paste, Ctrl+V, the currently 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

ツール

スケッチャーワークベンチのツールはスケッチャーワークベンチをロードすると表示されるSketcherメニューに配置されています。

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

Create sketch: Creates a new sketch and opens the Sketcher Dialog to edit it.

Edit sketch: Opens the Sketcher Dialog to edit an existing sketch.

Attach sketch: Attaches a sketch to selected geometry.

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.

Merge sketches: Merges two or more sketches.

Mirror sketch: Mirrors sketches along their X axis, Y axis, or origin.

Sketcher Edit Mode toolbar

Leave sketch: Finishes sketch edit mode and closes the Sketcher Dialog.

View sketch: Sets the 3D view perpendicular to the sketch plane.

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

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

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

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

Other

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

Sketcher geometries

These are tools for creating objects.

Point: Draws a point.

Line: Draws a line segment between 2 points. Lines are infinite regarding certain constraints.

Create arc:

Arc: Draws an arc segment from center, radius, start angle and end angle.

Arc by 3 points: Draws an arc segment from two endpoints and another point on the circumference.

Create circle:

Circle: Draws a circle from center and radius.

Circle by 3 points: Draws a circle from three points on the circumference.

Create conic:

Ellipse by center: Draws an ellipse by center point, major radius point and minor radius point.

Ellipse by 3 points: Draws an ellipse by major diameter (2 points) and minor radius point.

Arc of ellipse: Draws an arc of ellipse by center point, major radius point, starting point and ending point.

Arc of hyperbola: Draws an arc of hyperbola.

Arc of parabola: Draws an arc of parabola.

B-spline:

B-spline by control points: Draws a B-spline curve by its control points.

Periodic B-spline by control points: Draws a periodic (closed) B-spline curve by its control points.

B-spline by knots: Draws a B-spline curve by its knots. introduced in version 0.21

Periodic B-spline by knots: Draws a periodic (closed) B-spline curve by its knots. introduced in version 0.21

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.

Create rectangle:

Rectangle: Draws a rectangle from 2 opposite points.

Centered rectangle: Draws a rectangle from a central point and an edge point. introduced in version 0.20

Rounded rectangle: Draws a rounded rectangle from 2 opposite points. introduced in version 0.20

Create regular polygon:

Triangle: Draws a regular triangle inscribed in a construction geometry circle.

Square: Draws a regular square inscribed in a construction geometry circle.

Pentagon: Draws a regular pentagon inscribed in a construction geometry circle.

Hexagon: Draws a regular hexagon inscribed in a construction geometry circle.

Heptagon: Draws a regular heptagon inscribed in a construction geometry circle.

Octagon: Draws a regular octagon inscribed in a construction geometry circle.

Regular polygon : Draws a regular polygon by selecting the number of sides and picking two points: the center and one corner.

Create slot:

Slot: Draws an oval by selecting the center of one semicircle and an endpoint of the other semicircle.

Arc slot: Draws an arc slot consisting of two semicircles connected by two parallel concentric arcs. introduced in version 0.22

Create fillet/chamfer:

Fillet: Creates a fillet between two non-parallel edges.

Chamfer: Creates a chamfer between two non-parallel edges.

Edit edge:

Trim: Trims a line, circle or arc with respect to the clicked point.

Split: Splits an edge into two while keeping most of the constraints. introduced in version 0.20

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

External geometry: Creates an edge linked to external geometry.

Carbon copy: Copies the geometry of another sketch.

Toggle construction geometry: 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.

Coincident (unified): Can replace the Coincident and Point on object constraints. introduced in version 0.22

Coincident: Affixes a point onto (coincident with) one or more other points. It acts as a concentric constraint if two or more circles, arcs, ellipses or arcs of ellipses are selected.

Point on object: Affixes a point onto another object such as a line, arc, or axis.

Horizontal/Vertical constraints:

Horizontal/Vertical: Automatically applies Horizontal or Vertical constraint depending on the orientation of a line. introduced in version 0.22

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

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

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

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

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.

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

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

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:

Dimension: Provides context-sensitive dimensional constraint tool. introduced in version 0.22

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.

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.

Distance: Defines the length of a line, the perpendicular distance between a point and a line, the distance between two points, or, introduced in version 0.21, the distance between the edges of two circles.

Auto radius/diameter: Defines the radius of an arc, the diameter of a circle or the weight of a B-spline pole. introduced in version 0.20

Radius: Defines the radius of an arc or circle or the weight of a B-spline pole.

Diameter: Defines the diameter of an arc or circle.

Angle: Defines the internal angle between two selected lines.

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.

Special constraints

Refraction (Snell's law): Constrains two lines to obey a refraction law to simulate the light going through an interface.

Constraint tools

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

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

Activate/deactivate constraint: Enable or disable an already placed constraint.

Sketcher tools

Select unconstrained DoF: Highlights in green the geometry with degrees of freedom (DoFs), i.e. not fully constrained.

Select associated constraints: Selects the constraints of a Sketcher element.

Select associated geometry: Select Sketcher elements associated with constraints.

Select redundant constraints: Selects redundant constraints of a sketch.

Select conflicting constraints: Selects conflicting constraints of a sketch.

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

Select origin: Selects the origin of a sketch.

Select horizontal axis: Selects the horizontal axis of a sketch.

Select vertical axis: Selects the vertical axis of a sketch.

Offset geometry: Adds an equidistant outline around selected edges. introduced in version 0.22

Polar transform: Rotates and optionally copies (to create polar patterns) selected geometries. introduced in version 0.22

Scale transform: Scales and optionally copies selected geometries. introduced in version 0.22

Symmetry: Copies a Sketcher element symmetrically to a chosen line.

Array transform: Translates and optionally copies (to create linear patterns) selected geometries. introduced in version 0.22

Remove axes alignment: Remove axes alignment while trying to preserve the constraint relationship of the selection. introduced in version 0.20

Delete all geometry: Deletes all geometry 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 compatible geometry, edges and curves, into a B-spline.

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

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

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 an existing B-spline. introduced in version 0.20

Join curves: Joins two curves at selected end points. introduced in version 0.21

Sketcher visual

Switch virtual space: Allows you to hide all constraints of a sketch and make them visible again.

Show/hide B-spline degree: Shows or hides the display of the degree of a B-spline.

Show/hide B-spline control polygon: Shows or hides the display of the defining polygon of a B-spline.

Show/hide B-spline curvature comb: Shows or hides the display of the curvature comb of a B-spline.

Show/hide B-spline knot multiplicity: Shows or hides the display of the knot multiplicity of a B-spline.

Show/hide B-spline control point weight: Shows or hides the display of the weights for the control points of a B-spline.

Show/hide circular helper for arcs: Shows or hides the circular helpers (circle outlines) for arcs. introduced in version 0.22

Obsolete tools

Clone: Clones a Sketcher element. Not available in version 0.22 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 0.22 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 0.22 and above.

Move: Moves the selected geometry taking as reference the last selected point. Not available in version 0.22 and above.

Rectangular array: Creates an array of selected Sketcher elements. Not available in version 0.22 and above.

Preferences

Preferences: Preferences for the Sketcher Workbench.

Best practices

Every CAD user develops their 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.
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; Point on object constraint; Symmetric constraint.
If in doubt about the validity of a sketch once it is complete (features turn green), close the Sketcher dialog and use Validate sketch.

チュートリアル

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