Sketcher Workbench/スケッチャーワークベンチ

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This page is a translated version of the page Sketcher Workbench and the translation is 2% complete.
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Sketcher workbench icon

はじめに

スケッチャーワークベンチ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。

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。

A fully constrained sketch

Basics of constraint sketching

スケッチ拘束の基本

スケッチャーがどのように動作するか説明するには"従来"の製図方法と比較するとわかりやすいでしょう。

Traditional Drafting

従来の製図

"従来"のCAD製図方法は過去の製図板を用いた方法を受け継いでいます。(2次元)正射影図を手書きすることで製図(いわゆる青写真)を作成します。物体は意図したサイズ、寸法に合わせて正確に描画されます。もし点(0, 0)から伸びる100mmの水平線を描きたければまずラインツールを選択し、画面をクリックするか座標(0, 0)と入力して始点を設定した後、終点をクリックするか座標を(100,0)を入力します。あるいは位置を気にせずに線を描き、後から位置を調整します。形状を描き終わったらそれらに寸法を追加します。

Constraint Sketching

拘束スケッチ

スケッチャーの方法は全く異なります。物体を厳密に描く必要はありません。なぜなら物体は後で拘束をかけることによって定義されるからです。物体はおおまかに描けばよく、拘束をかける前であれば変更も可能です。実際の所、物体は"流動的"で動かしたり、伸ばしたり、回転させたり、拡大縮小させたりといったことが可能です。これによってデザイン作業がとても柔軟なものになります。

What are 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。

What the Sketcher is not good for

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。

もし印刷用の2次元表示を作成するだけで3次元モデルが必要ないのであれば製図ワークベンチをチェックしてください(製図ワークベンチでも2次元形状が作れることを記憶に留めておいてください。今のところスケッチャーでは使用できない機能、例えばB-スプラインなどを使うこともできます)。

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

Sketching Workflow

スケッチは常に2次元(2D)です。 ソリッドを作成するには、囲まれた1つの領域の2Dスケッチを作成し、次にPaddedまたはRevolvedで3次元を追加して、2Dスケッチから3Dソリッドを作成します。

スケッチが互いに交差する線分、Pointが線分上に直接ない場所、または隣接する線分の端点間にギャップがある場所では、PadまたはRevolveはソリッドを作成しません。 この規則の例外は、それがConstruction(blue)Geometryには適用されないことです。

囲まれた領域の内側に、重ならない小さな領域を含めることができます。 3Dソリッドを作成すると、これらは無効になります。

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 Check geometry to ensure there are no features in the Sketch which may cause later problems.

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 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.
  • Reorient sketch: Allows you to attach the sketch to one of the main planes.
  • Validate sketch: Analyze and repair a sketch that is no longer editable, has invalid constraints, or is missing coincident constraints.
  • Mirror sketch: Mirror a sketch along the x-axis, the y-axis or the origin.

Sketcher Edit Mode toolbar

  • View sketch: Sets the model view perpendicular to the sketch plane.
  • View section: Creates a section plane that temporarily hides any matter in front of the sketch plane.

Sketcher edit tools toolbar

Other

  • 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.

  • 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.
  • Create conic:
  • Ellipse by center: Draws an ellipse by center point, major radius point and minor radius point.
  • Arc of ellipse: Draws an arc of ellipse by center point, major radius point, starting point and ending point.
  • B-spline:
  • 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.
  • 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.
  • Create fillet:
  • Fillet: Creates a fillet between two non-parallel lines.
  • Corner-preserving fillet: Creates a fillet between two non-parallel lines while preserving their (virtual) intersection.
  • Edit edge:
  • Trim: Trims a line, circle or arc with respect to the clicked point.
  • Extend: Extends a line or an arc to a boundary line, arc, ellipse, arc of ellipse or a point in space.
  • 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: 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: 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:
  • 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.
  • 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.
  • 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.

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:

Sketcher tools

  • Show/hide internal geometry: Recreates missing/deletes unneeded internal geometry of a selected ellipse, arc of ellipse/hyperbola/parabola or B-spline.
  • Symmetry: Copies a sketcher element symmetrical to a chosen line.
  • Clone: Clones a sketcher element.
  • Copy: Copies a sketcher element.
  • Move: Moves the selected geometry taking as reference the last selected point.

Sketcher B-spline tools

Sketcher visual

Obsolete tools

  • Close shape: Creates a closed shape by applying coincident constraints to endpoints. Not available in version 0.21 and above.
  • Connect edges: Connect sketcher elements by applying coincident constraints to endpoints. Not available in version 0.21 and above.

Preferences

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.
  • 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 Part Workbench and run Check geometry.

チュートリアル

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.