What defines a solid part 1

[EngJW]

I am curious about how the final part is defined in Solidworks, or any other solid program.

For example, a part about an axis could be created in two different ways. You could draw the profile and revolve it. You could also start with a basic shape like bar stock and extrude-cut away from it.

Is the mathematical definition of the final part the same in each case, or does it depend on the number of steps used to create it?

Thanks,
John Woodward

 

[SBaugh]

The less the steps in creating it or the better design intent used is the best method.

If you can make the whole part in one feature and a single sketch. Then I make the revolve. Doing it the other way is non-productive, because you have 2 sketches and if you have to modify the first sketch, then the second will also have to be modified. Were as with one sketch you can make a few changes and walla part modified.

Regards,

Scott Baugh, CSWP
3DVision Technologies

http://www.scottjbaugh.com

Merry Christmas
faq731-376
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[TheTick]

The solid vs. closed surface debate has surfaced before with no solid conclusion.

Without a doubt, a solid (in the computer generation sense) is, at minimum, a collection of trimmed surfaces (faces) joined to form a completely bounded 3-D region. After that, there is much debate and no real consesus as to what a solid is.

If you delve into the inner workings of a CAD program, you will find that nothing is solid until the program decides it is solid.

For example, take a simple extruded rectangle. It has six faces: two planar end faces defined by position and shape of the profile, and four side faces each defined by the linear travel of the line segments of the profile. The CAD program then joins the surfaces and confers on it the title "solid".

"Customer satisfaction, while theoretically possible, is neither guaranteed nor statistically likely.--E.L. Kersten

http://www.EsoxRepublic.com

 

[jack3108]

The last answer from TheTick remines me the way one used to build (a couple of generations ago) a SOLID in CATIA.

First - it was a WIREFRAME
Next - on the wireframe build SURFACES or FACES (face being relimited surface was actually lying on the surface)
Next - join all the faces and surfaces into VOLUME (no "leaks")
Final - conversion from volume to SOLID.

Obviously the next step could be carried out only after the preceeding step was succesful.

Looks like the designers of the present era CAD systems managed to simplify the proces (at least for the end user)

 

[ctopher]

I have always seen a solid as: if you can define mass properties ... i.e. density, it's a solid. A file that can also be run thru FEA.

 

[EngJW]

Let me attempt to clarify the first question-

If several designers build the same part in Solidworks but each one uses a different method or different sequence of steps, is the final part identical as far as the geometric definition is concerned, or does the computer only see all the steps used to create it?

I think the part would be the same. If you made a rapid prototype from it, I don't think the process would go through all the steps used to build the model.

 

[ctopher]

I don't think either way a rapid prototype would go thru any steps, same as if doing FEA Cosmos. Either way, the solid is the same ... different file sizes and times to load, but a solid is a solid. If I made sense

 

[MadMango]

I agree that the end results would be the same.

[green]"But what... is it good for?"[/green]
Engineer at the Advanced Computing Systems Division of IBM, 1968, commenting on the microchip.
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[TheTick]

... is the final part identical as far as the geometric definition is concerned, or does the computer only see all the steps used to create it?

Both.

The SW file contains the list of features required to generate the part. It also contains the raw parasolid rendition of that part's bodies. This is what makes it possible for assemblies to have lightweight components.

"Customer satisfaction, while theoretically possible, is neither guaranteed nor statistically likely.--E.L. Kersten

http://www.EsoxRepublic.com

 

[macPT]

If you create the same part in different ways and save as IGES, the result files are different (I don't know why, but different data is written).

But if you import these IGES files back into SW, the imported dumb solid is exactly the same (check mass properties).

So the solid is the same. That's why addins like Cosmos doesn't care on how you build your model. They care about the result solid, which is the same.

ctopher, you made sense!

Regards

 

[TheTick]

IGES is a lot smarter than it gets credit for. Much depends on how the source application writes the file, though.

For instance, IGES has surface categories for revolved surfaces and for primitive cylinders. Depending on how you created your part, your application may write the surface definition in different ways.

 

[Heckler]

I believe this article will answer your question John.

http://www.cadalyst.com/cadalyst/article/articleDetail.jsp?id=79619

Best Regards,

Heckler

"Never underestimate the power of very stupid people in large groups" John Kenneth Galbraith