Surfaces vs Solids - Which?

This should be very enlightening:

Maybe it was CS 102. I'm not so sure now. Interesting stuff, anyway.

All roads lead to Rome. If you can get what you need by using only solid features, great.

When a CAD program builds a solid feature, it is going through dozens of steps to do so. For instance, to make an extrusion, curves are swept to determine surfaces, surfaces are trimmed into faces, faces are knit into bodies, and a solid body is brought into being.

Surface-based modelling is mostly just doing these things manually (usually because the geometry doesn't lend itself to conventional features). Surface patches of an object are built one-at-a-time. Curves and planes define surfaces, surfaces are trimmed and knit together and (usually) knit or thickened into a solid.

There are some things that are difficult or very inefficient to do in solids. One of the tests that I use for the surfaces/solids question is if I'm drawing a lot of lines that don't do anything other than close the sketch in order to make a solid. Sometimes you combine the techniques to do "hybrid" design. Surfaces are also good ways to keep a copy of a face before fillets or cuts were added to the solid. Also, just having additional tools under your belt and understanding how to apply them is always a help.

Of course Ed Eaton has written the SW surfacing bible, but I've got a user group presentation that was based on a Desktop Engineering article I wrote on the "hybrid" topic.

Matt

Here are some more tutorials. Some of the beginning tutorials use surfaces to do parts that could be more easily done with solids - but gives you an idea how to use surfaces where solids tools would not work. In the end the goal is to get a solid. Educational licenses are limited to latest release-1 and my tutorials are written over the summer so these tutorials are two releases out-of-date, but many of the procedures are the same.

'Try Surfacing for Blockheads', the first in the list of tutorials at dimontegroup.com. It was written to answer just this question. I think I wrote almost the complete script in the speaker notes on the powerpoint slides. For what it is worth, I will be presenting this (slightly updated) at the West coast user conference, the midwest combined group AND at the Grafix systems midwest user conference.

Thanks for all the input - I'll have to go thru some of these tutorials!

Man! talk about slow download speeds - must be busy sites

So parts will stay where you put them. All those weightless curves, surfaces and b-reps get scattered all over the place with the least little breeze. Never mind that intelligent use of appropriate representations allows development and communication of intent with a fraction of the overhead incurred using only solid modeling.

It's a mindset peculiar to small system 'mechanical' CAD designers rooted in the lower end CAD systems' development strategies. They licensed and integrated canned components rather than developing full functioned systems from the ground up exposing each layer of functionality to the user, most of whom have no use for the functions anyway. The results were affordable programs, cart (solids)-before-the-horse (surfaces) development trends and a sometimes irrational fixation with so called 'solids'.

Worth mention, too, is how few understand that solid modeling is a description of technique, not end result. The results are simply limited by the technique.

Solids have an inside, and an outside. The inside of a solid is a bounded volume (so is the outside, I suppose). Bounded volumes have specific meanings in the physical world; surfaces, only metaphysical ones.

Surfaces also have two sides: there's one side, and then there's the other side. Parametrically, they are 2D: U and V. Their cross-sectional area is zero, meaningless. Surfaces are hypothetical abstractions useful only to define volumes, as lines exist only to bound areas. In doing so, ipso facto, "the end goal is to get a solid."

Your a trolls troll (compliment)

Solid this, solid that.Big woopie. I believe in solids for mold design 100%. After that doesnt matter, whatever gets the job done faster. Solids for wire edm makes me cough I laugh so hard@! WTF? Solids for a 2 d contour? And milling, well, show me a cam system worth a shot amd I'll use solids on it. Until thenI'll stick to iges.

Troll with Blinns and Phongs Surfaces bounder darkly In the end, solids.

"vinny" wrote in news:430f978f$0$25279$ snipped-for-privacy@authen.white.readfreenews.net:

I agree. In mold design, solids are a must anymore but in CAM yer not machining a solid yer machining a surface or surfaces.

And another cigar! Only problem with solids going to 2d is that ya have all them teeny-weeny lil lines that duplicate all over. Even from a 2d drawing that references the solid model. Its that kinda s*it that irks me.

Iges? Eeeeek. Gotta be the worst damn translator out there Vinny. I hate Iges almost as much as I hate some MI part engineers. :)

Bing

Unless you're machining on meshes...

--Mitch

Tessellation has come a long way Cliff.

It is unless the software is designed accordingly. Hardware is so fast today that the mach8ining tesselation is often created on the fly and then discarded unless you specifically elect to save it.

Only the real hacks still do this. They exist but they are very cheap systems. Even RhinoCam at 1K is regenerative. That is the industry buzz word in many places - "Regenerative". Cim Link used to make a big deal about it. They did, IMHO, have a great engine though.

Not much of any issue except to purists like you and I Cliff. Todays kids don't know different and it doesn't matter much. Nobody really cares since there is not competetive dissadvantage in the market place.

Sweet Jesus who in their right mind would want to remember THAT :>)

"Mitch" wrote in news:43109d12_1 @news.bluewin.ch:

Heh, roger that.

Bing

Why on earth do you "NEED" soldis for mould design. I use Solidworks for product design, but I would never use it for mould tool design, it simply is not up to my usual mould tool software -which is purely surface based. When it comes to defining complex 3D split lines and shut-outs the tools in Solidworks don't cut it for me.

Regards

Kevin