About Part and PartDesign Wiki page

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jpg87
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About Part and PartDesign Wiki page

Postby jpg87 » Thu May 13, 2021 2:23 pm

In this post I would like to submit my proposals for the "Part WB and PartDesign WB" wiki page for discussion.
Here are some changes or additions that I propose :

Part Workbench Concepts
Part Workbench is a Constructive Solid Geometry (CSG) style modeling. The operator combines various primitives to end up with a representation of the desired shape. (In fact, Part Workbench goes one step further than just primitives and allows the operator to use a sketch+extrude operation to create its own primitives.)
When each primitive or shape is created, it has no relationship to other objects created, it is a single solitary solid.
This condition ...



PartDesign Workbench Concepts
In the PartDesign Workbench, the Body object is constructed directly as a single cumulative solid.

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.


(question : what do you mean about « proxy »?)

Note :
At each time of construction, the last function used is the "Tip", which can be defined as "active stage in the construction of the object" or "stage preceding the next action in the construction of the object".
When the object's drawing is complete, Tip is naturally the last stage or feature of the construction.
But if desired, in case of forgetting, any feature of the construction can be provisionally declared as Tip: it then becomes the step preceding the next action in the construction of the object, which means that new feature(s) can be inserted anywhere in the construction, ON CONDITION NOT TO CREATE ANY INCOMPATIBLE WITH THE SUITE.
When everything is finished, you have to redeclare the last feature as Tip, which corresponds to the finished object.

...
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. The pad can exist separately (Tip on pad) but the cone cannot exist separately (Tip on cone = pad + cone).


The Ramifications
Although not recommended, it is possible to combine tools from Part WB and PartDesign WB, provided you know what you are doing. For example :
People get caught when they attempt to use some feature under the Body (rather than the Body itself) as one selection of a Part Workbench Boolean operation. This is a problem, because the selected feature does not represent THE complete solid.
...



The Caveats
… the Mirror is operating on the underlying feature …

I disagree here : the Mirror does not necessarily apply to the last step or even to a single step. You must select the feature(s) on which you want to apply the Mirror. The same goes for the other transformation features of PartDesign (Linear or Polar pattern).


Comparison
I think that a comparison in pictures on the same example can facilitate the understanding of the differences. So I therefore propose below the same example built with each of the two workbenches. Of course, there are always several possible construction timelines with each workbench.
Note : The starting stages could have been the same.

PartWBvsPartDesignWB01.jpg
PartWBvsPartDesignWB01.jpg (102.91 KiB) Viewed 811 times
PartWBvsPartDesignWB02.jpg
PartWBvsPartDesignWB02.jpg (90.86 KiB) Viewed 811 times
PartWBvsPartDesignWB03.jpg
PartWBvsPartDesignWB03.jpg (101.19 KiB) Viewed 811 times
PartWBvsPartDesignWB04.jpg
PartWBvsPartDesignWB04.jpg (63.11 KiB) Viewed 811 times
PartWBvsPartDesignWB05.jpg
PartWBvsPartDesignWB05.jpg (98.13 KiB) Viewed 778 times

Info:
If you think my remarks and example are useful, I will provide all the pictures needed, or try (1st time!) To complete the wiki myself.
My website : http://help-freecad-jpg87.fr updated 2021/05/27
chrisb
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Re: About Part and PartDesign Wiki page

Postby chrisb » Thu May 13, 2021 5:29 pm

Thanks for working on this. I have only a few suggestions:
jpg87 wrote: Thu May 13, 2021 2:23 pm Part Workbench is a Constructive Solid Geometry (CSG) style modeling.
Part Workbench is essentially/basically/mainly Constructive Solid Geometry (CSG) style modeling
(In fact, Part Workbench goes one step further than just primitives and allows the operator to use a sketch+extrude operation to create its own primitives.)
I wouldn't call sketch based objects primitives anymore. I would rather say "objects" or "base objects" as counterpart to BaseFeatures.
When each primitive or shape is created, it has no relationship to other objects created, it is a single solitary solid.
This condition ...
I'm not sure what this means with respect to sketches that are attached to another object.
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.
I don't agree on the first sentence. Every feature above Tip represents a solid as well, but only Tip is what the world outside of the Body sees.
Although not recommended, it is possible to combine tools from Part WB and PartDesign WB, provided you know what you are doing. For example :
I wouldn't say, that the combination isn't recommended in general. Think of arrays or mirrors of whole bodies, especially when they are not intersecting. Nevertheless it should be mentioned that such combinations are far from trivial. Perhaps Although not recommendedfor newcomers is a better choice.
Comparison
I think that a comparison in pictures on the same example can facilitate the understanding of the differences.
I fully agree on that! But I would like to see a more suggestive example, where indeed the equivalent operations are applied on both sides, so that it becomes clearer where the differences are. At the end I would add an image of the tree views of both approaches.
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drmacro
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Re: About Part and PartDesign Wiki page

Postby drmacro » Thu May 13, 2021 5:54 pm

FWIW @david69 contacted me about this page I wrote a while back, he was interested in translating it.

https://wiki.freecadweb.org/Part_and_PartDesign
Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."

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jpg87
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Re: About Part and PartDesign Wiki page

Postby jpg87 » Sat May 15, 2021 7:17 am

drmacro wrote: Thu May 13, 2021 5:54 pm FWIW @david69 contacted me about this page I wrote a while back, he was interested in translating it.
Hello @drmacro,
thank you for starting this page. I will try to make my contribution. If I have any difficulties, I will contact @david69 to resolve them.

chrisb wrote: Thu May 13, 2021 5:29 pm I have only a few suggestions:
thank you also for your suggestions. I am starting ...
My website : http://help-freecad-jpg87.fr updated 2021/05/27
drmacro
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Re: About Part and PartDesign Wiki page

Postby drmacro » Sat May 15, 2021 9:49 am

jpg87 wrote: Sat May 15, 2021 7:17 am
drmacro wrote: Thu May 13, 2021 5:54 pm FWIW @david69 contacted me about this page I wrote a while back, he was interested in translating it.
Hello @drmacro,
thank you for starting this page. I will try to make my contribution. If I have any difficulties, I will contact @david69 to resolve them.

chrisb wrote: Thu May 13, 2021 5:29 pm I have only a few suggestions:
thank you also for your suggestions. I am starting ...
He and I have been discussing the paragraph about people getting caught by mixing Part and PartDesign...I don't remember if made final version.
Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."

My beginners, written treatise: Learning FreeCAD
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jpg87
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Re: About Part and PartDesign Wiki page

Postby jpg87 » Sat May 15, 2021 6:18 pm

To
drmacro wrote: Sat May 15, 2021 9:49 am...
and
chrisb wrote: Thu May 13, 2021 5:29 pm...
... and to all the others!
I just finished a 1st version.
Thank you for your comments.
My website : http://help-freecad-jpg87.fr updated 2021/05/27