Sketcher Workbench/zh-cn



The Sketcher Workbench is used to create 2D geometries intended for use in the Part Design Workbench and other workbenches. Generally a 2D geometry is considered the starting-point for most CAD models - a simple 2D sketch can be 'extruded' into a 3D shape, further 2D sketches can be used to create pockets in the surface of this shape and sketches can be used to define 'pads' (extrusions) on the surface of 3D objects. Along with boolean operations, the sketcher forms the core of generative solid shape design.

素描工作台本身具有约束条件 - 允许将2D形状约束到精确的几何定义. 以及一个约束求解器，它计算二维几何约束范围，并允许对素描自由度的交互式探索.

约束素描的基础
为了解释素描器的工作原理，将其与“传统的”起草方式进行比较可能是有用的.

传统起草
CAD绘图的传统方式继承于旧的绘图板. 正交（2D）视图 手动绘制，用于生产技术图纸（也称为蓝图）. 对象被精确地绘制到预期的尺寸或尺寸上. 如果要从（0,0）开始绘制长度为100mm的水平线，您可以激活线条工具，点击屏幕或输入第一个点的（0,0）坐标，然后再次点击或在（100,0）处输入第二点坐标. 或者你会画你的线，而不考虑它的位置，然后移动它. 绘制几何图形后，可以向其添加尺寸.

约束素描
素描远离这个逻辑. 对象不需要完全按照您的意图进行绘制，因为它们将在稍后被约束定义. 对象可以松散绘制，只要不受约束，就可以进行修改. 它们实际上是“浮动”，可以移动，拉伸，旋转，缩放等等. 这在设计过程中给予了很大的灵活性.

什么是约束？
使用约束来限制对象的自由度. 例如，没有约束的线条具有4 自由度（简写为“DOF”）：可以水平或垂直移动，可以被拉伸，并且可以旋转.

应用水平或垂直约束或角度约束（相对于另一条线或与其中一条轴）将限制其旋转能力，从而使其具有3个自由度. 锁定其原点之一的点将消除另外2个自由度. 并且应用维度约束将消除最后的自由度. 然后，该行被认为是“完全受限制的”.

多个对象可以彼此约束. 可以通过其中一个点与重合点约束连接两条线. 可以在它们之间设置一个角度，或者它们可以垂直设置. 一条线可以与弧或圆相切，依此类推. 具有多个对象的复杂素描将具有多种不同的解决方案，并使其“完全受约束”，这意味着基于所应用的约束只能达到其中一种可能的解决方案.

有两种约束：几何和尺寸. 它们在下面的'工具'部分中详细介绍.

素描不擅长于
素描器不打算制作2D蓝图. 素描一旦用于生成实体特征后，会自动隐藏. 约束仅在素描编辑模式下可见.

如果您仅需要生成2D视图进行打印，并不想创建3D模型，请查看草图工作台（请注意，草图工作台也可用于创建此时素描器中不可用的2D几何，如B-Splines. ）

素描工作流程
素描总是二维（2D）. 要创建一个实体，创建单个封闭区域的2D素描，然后垫高或旋转以添加第三维，从2D素描创建3D实体.

如果草图具有彼此交叉的段，其中一个点不直接位于段上的位置，或相邻段的端点之间存在间隙的位置，垫高或旋转将不会创建一个实体. 这个规则的例外是它不适用于建筑（蓝色）几何.

在封闭区域内，我们可以有较小的非重叠区域. 当创建3D实体时，这些将变为空白.

工具
素描工作台工具都位于加载素描工作台时出现的素描菜单中.

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.

Tutorials

 * Sketcher Tutorial
 * Sketcher tutorial for beginner
 * Sketcher Micro Tutorial - Constraint Practices