The essence of the problem of scaling objects in FreeCAD up to 0.19 inclusive
Topological naming problem: https://youtu.be/V1Viqgn3_W8?t=169
What can we scale: https://youtu.be/V1Viqgn3_W8?t=275
Creating a simple model in Part: https://youtu.be/V1Viqgn3_W8?t=349
About Draft Tool -> Scale: https://youtu.be/V1Viqgn3_W8?t=402
FreeCAD Toolbar Customization: https://youtu.be/V1Viqgn3_W8?t=499
Trying to work with Draft -> Scale: https://youtu.be/V1Viqgn3_W8?t=573
Sometimes, when working in FreeCAD, you may want to scale an object composed of different bodies, with modifications applied to them.
And here you come across the fact that in the Part and PartDesign workbenches there is simply no such seemingly primary function.
The question arises: "Why?" In short, somewhere I saw an explanation in the English forum that in fact such a need to scale the entire object as a whole may arise, very rarely, and this is the lot of beginners in CAD.
In addition, FreeCAD is only a developing program, apparently, the implementation of the correct scaling of complex objects is not an easy task. After all, FreeCAD is a parametric CAD system, and in PartDesign, moreover, bodies are mainly formed from sketches with the subsequent application of so-called features (parametric modifications) to them.
In the discussions on the English forum that I studied, the developers make it clear that if you are serious about working, then editing the sketch and editing the parameterized operations applied further along the chain should be enough for you to scale the object.
And if you still have a desire to scale everything at once, then it is easier to use another software program that will stupidly take your imported file in some STEP format and resize everything in it at once, rather than force a constantly "thinking" that maintains a modification tree FreeCAD strain and calculate the interaction of all parameters.
(When such a need may arise?.. well, for example, you make a mold for casting something and the material shrinkage has not been calculated, or you are making a model for 3d printing). For example, in the case of 3D printing, if you are making an STL model, there is a scaling function in 3D printers.
If you want to scale not the whole model at once, but part of it, then the task is even more difficult. This is where the "Topological naming problem" comes into play https://www.freecadweb.org/wiki/Topolog ... ng_problem. An article in English, briefly about the fact that when individual elements are changed, subelements, such as faces, can be formed or deleted, and at the moment the problem inside FreeCAD (and many other CAD systems) of correct tracking of what became what after the operation has not been solved, that is, for example an internal permutation of the identifiers of vertices, edges, faces that is incomprehensible to the user may occur, and if, in turn, on the basis of some face another object was created, then it may unexpectedly move somewhere in an incomprehensible direction .. Probably better I will make a separate video on topic "Topological naming problem".
Upd See the comment below Topological naming problem in CADs.
So, scaling 3d objects directly in FreeCAD (I'll make a reservation, without any third-party plugins) is possible only if these objects are not parameterized. If the object is parameterized (and in most cases we work just with parameterized objects created in the Part, PartDesign workbenches), then at the moment there is no way to directly scale the parameterized objects! At most, you can create a scaled copy or clone of this object. The resulting clone or copy will be a single solid body without any components and their parameters. I think there is no need to explain the difference between a clone and a copy, just saying the clone after creation changes when the original object changes, and the copy does not depend on the original object. This body itself will have only a set of standard parameters (position, etc.). The clone will have one more specific parameter - the scale, which you can change in the object properties panel on the "Data" tab.
The Scale tool itself is initially available in the Draft workbench. But this does not mean that it only works with 2D-Draft objects.
This tool works with objects of type Part, and in freeCAD almost all objects, including 2D objects, inherit from the Part class:
FreeCAD classes scheme
it is therefore not surprising that this tool works with all types of objects.
The fact that the "Scale" button is initially available in the "Draft" workbench is a convention. If suddenly (I do not know in what cases such a need may arise), you often need to use the "Scale" tool, then you can slightly customize the toolbar and make the "Scale" tool appear in any workbench or even in all workbenches at once.
By the way, the online documentation for the Draft → Scale tool says so:
Modify original. The original object will have its size modified. This will only work with Draft objects and non-parametric Part shapes.
Create a copy. A scaled copy of the original object will be created. This will work for all object types, but only the copies of Draft objects will be parametric.
Note: a copy is a completely different object from the original shape; it will be created at the specified scale, and then will have its own set of properties. On the other hand, a Draft Clone is linked to the original shape and the only property that can be changed is the scale.
I wanna mention that in versions 0.18 & 0.19 the copying option with parameterized objects works poorly, cloning works.