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Le point à retenir est la partie solide et solitaire et la partie qui les combine.
Le point à retenir est la partie solide et solitaire et la partie qui les combine.


==Concepts de l'atelier PartDesign==
==PartDesign Workbench Concepts==


In the PartDesign WB the Body object represents a single solitary cumulative solid. The first lump created under the Body (be it a Pad from a sketch, or a BaseFeature from outside the Body) represents a lump of raw material that will be further processed to refine it to the desired final shape (solid). It is cumulative in the sense that each operation adds or removes material. The lowest/last operation (the current Tip of the Body) is the current state. Any other feature under the Body but above the Tip, does not represent a complete/stand alone solid. Only the Body (basically a proxy for the tip) or the Tip represent a complete solid.
In the PartDesign WB the Body object represents a single solitary cumulative solid. The first lump created under the Body (be it a Pad from a sketch, or a BaseFeature from outside the Body) represents a lump of raw material that will be further processed to refine it to the desired final shape (solid). It is cumulative in the sense that each operation adds or removes material. The lowest/last operation (the current Tip of the Body) is the current state. Any other feature under the Body but above the Tip, does not represent a complete/stand alone solid. Only the Body (basically a proxy for the tip) or the Tip represent a complete solid.

Revision as of 14:35, 8 May 2021

Présentation

Il y a eu beaucoup de discussions au cours des années sur les différences et les conséquences de l'utilisation des ateliers Part et PartDesign.

Il est bon d'utiliser l'un ou l'autre jusqu'à ce que l'utilisateur soit à l'aise avec l'un, puis d'apprendre l'autre. Il est aussi généralement recommandé aux nouveaux utilisateurs de ne pas les mélanger avant d'en avoir compris les implications.

Parlons de ces implications.

Concepts de l'atelier Part

On dit souvent que l'atelier Part est davantage unemodélisation de type CSG. C'est là que l'utilisateur combine diverses primitives pour aboutir à un morceau de la forme souhaitée. (En fait, l'atelier Part va un peu plus loin que les simples primitives et permet à l'utilisateur d'utiliser une opération d'esquisse+extrusion pour créer également des formes aléatoires). Lorsque chaque primitive ou forme est créée, elle n'a aucune relation avec les autres objets créés, c'est un solide unique et solitaire.

Solides isolés


Cette condition demeure jusqu'à ce que l'utilisateur utilise une opération pour les combiner (généralement une opération booléenne qui les additionne ou les soustrait).

Le point à retenir est la partie solide et solitaire et la partie qui les combine.

Concepts de l'atelier PartDesign

In the PartDesign WB the Body object represents a single solitary cumulative solid. The first lump created under the Body (be it a Pad from a sketch, or a BaseFeature from outside the Body) represents a lump of raw material that will be further processed to refine it to the desired final shape (solid). It is cumulative in the sense that each operation adds or removes material. The lowest/last operation (the current Tip of the Body) is the current state. Any other feature under the Body but above the Tip, does not represent a complete/stand alone solid. Only the Body (basically a proxy for the tip) or the Tip represent a complete solid.

Cumulative Body Solid

This image shows a Body. It is a cumulative solid that consists of a padded sketch and a cone primitive. This is a single solid. Neither the pad or the cone can exist separately.

(Another thing mentioned often is a Body MUST be a single contiguous solid. This means all geometry created by a feature in the Body must touch it's predecessor.)

The Ramifications

People get caught when they attempt to use some feature under the Body (rather than the Body itself) as one selection of a Part WB Boolean operation. This is a problem, because the selected feature does not represent a complete solid.

In a sense, from a Part WB standpoint, the Body represents another primitive. So, using a Body (remember it is a proxy for the tip) and a Part WB object to do a Boolean is valid. But the resulting object is a Part WB object. And, thus PartDesign WB tools can't be used on it any longer.

And, it can get even more complicated. If you create a new Body and drag the result from the previous paragraph into it, a BaseObject is created. And you can go off an use the PartDesign WB tools on it.

The Caveats

There is a caveat with the Tip and it's representation of the single solid in the Body. If the tip is a subtractive feature and is used in a dress up operation, for instance a Mirror, the Mirror is operating on the underlying feature (a pocket for example). Thus the cumulative solid is not mirrored, but the subtractive feature is. The result of this must create a single solid.

In this example, a mirror of the tip (which is the pocket of the slot) around any of the base planes, or even a face of the solid will not produce a mirrored solid of the entire model. (In fact, it will produce a Mirrored feature in the tree that is essentially empty.)

Solitary solids

In this example, a mirror of the tip (which is the pocket of the slot) is performed around the datum plane and produces a mirrored slot:

Solitary solids

See the PartDesign Mirrored tool wiki page for more information.

Conclusion

Part and PartDesign workbenches can be used together with some care, creating quite complex models.

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