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.
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
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Základy vazeb v náčrtu
Pro vysvětlení funkce Skicáře může být užitečné porovnání s "tradičním" způsobem kreslení.
Traditional Drafting
The traditional way of CAD drafting inherits from the old drawing board. Orthogonal (2D) views are drawn manually and intended for producing technical drawings (also known as blueprints). Objects are drawn precisely to the intended size or dimension. If you want to draw an horizontal line 100mm in length starting at (0,0), you activate the line tool, either click on the screen or input the (0,0) coordinates for the first point, then make a second click or input the second point coordinates at (100,0). Or you will draw your line without regard to its position, and move it afterwards. When you've finished drawing your geometries, you add dimensions to them.
Skicování s vazbami
Skicář se vzdaluje od této logiky. Objekty nemusejí být kresleny přesně tak jak zamýšlíte, protože budou definovány později pomocí vazeb. Objekty mohou být kresleny volně a pokud nejsou vazbeny mohou být upravovány. Provedením jsou "plovoucí" a mohou být posunovány, natahovány, otáčeny, lze jim měnit měřítko, atd. To dodává velkou flexibilitu v procesu návrhu.
What are constraints?
Instead of dimensions, Constraints are used to limit the degrees of freedom of an object. For example, a line without constraints has 4 Degrees Of Freedom (abbreviated as " DOF "): it can be moved horizontally or vertically, it can be stretched, and it can be rotated.
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.
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.
Jsou dva druhy vazeb: konstrukční a rozměrové. Detailně jsou rozebrány v sekci 'Nástroje' dále.
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.
Jestliže potřebujete vytvářet pouze 2D pohledy pro tisk a nepotřebujete vytvářet 3D modely, podívejte se na Pracovní plochu kreslení (a nezapomínejte na to, že pracovní plocha Kreslení je také užitečná pro vytváření 2D konstrukcí nedostupných v současné době ve Skicáři, jako je třeba B-křivka).
Postup práce ve Skicáři
Bude přidáno
If the 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. 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.
Nástroje
Nástroje pracovní plochy Skicář jsou umístěny v menu Skicář, které se zobrazí když natáhnete pracovní plochu Skicář.
Sketcher Geometries
These are tools for creating objects.
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Bod: Draws a point -
Oblouk: Draws an arc segment from center, radius, start angle and end angle -
Kružnice: Draws a circle from center and radius -
2-Bod Přímka: Draws a line segment from 2 points -
Lomená čára (multiple-point line): Draws a line made of multiple line segments -
Obdélník: Draws a rectangle from 2 opposite points -
Zaoblení: Makes a fillet between two lines joined at one point. Select both lines or click on the corner point, then activate the tool. -
Oříznutíí: Trims a line, circle or arc with respect to the clicked point. -
Povrchový Náčrt: Creates an edge linked to external geometry. -
Změna konst.módu: Toggles an element to/from construction mode. A construction object will not be used in a 3D geometry operation.
Sketcher Constraints
Constraints are used to set rules between sketch elements, and to lock the sketch along the vertical and horizontal axes.
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Lock: Creates a lock constraint on the selected item by setting vertical and horizontal dimensions relative to the origin (dimensions can be edited afterwards). -
Coincident: Creates a coincident (point-on-point) constraint between two selected points. -
Point On Object: Creates a point-on-object constraint on selected items. -
Horizontal Distance: Fixes the horizontal distance between 2 points or line ends. If only one item is selected, the distance is set to the origin. -
Vertical Distance: Fixes the vertical distance between 2 points or line ends. If only one item is selected, the distance is set to the origin. -
Vertical: Creates a vertical constraint to the selected lines or polylines elements. More than one object can be selected. -
Horizontal: Creates a horizontal constraint to the selected lines or polylines elements. More than one object can be selected. -
Length: Creates a length constraint on a selected line. -
Radius: Creates a radius constraint on a selected arc or circle. -
Parallel: Creates a parallel constraint between two selected lines. -
Perpendicular: Creates a perpendicular constraint between two selected lines. -
InternalAngle: Creates an internal angle constraint between two selected lines. -
Tangent: Creates a tangent constraint between two selected entities, or a colinear constraint between two line segments. -
Equal Length: Creates an equality constraint between two selected entities. If used on circle or arcs, the radius will be set equal. -
Symmetric: Creates a symmetric constraint between 2 points with respect to a line.
Other
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New Sketch: Creates a new sketch on a selected face or plane. If none were selected, the default work plane XY will be used. -
View sketch: Sets the model view perpendicular to the sketch plane. -
Map sketch: maps a sketch to the previously selected face of a solid. -
Leave Sketch: Leave the Sketch editing mode. - Sketcher Reorient: Allows you to change the position of a sketch
Dobrá praxe
Každý uživatel CADu si časem vytvoří svůj vlastní způsob práce, ale je několik obecných principů, které je dobré následovat.
- 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.