Surfaces vs Solids - Which?

Was recently playing around with Mike J. Wilsons "Ship In a Bottle", and as
I looked to see how it was made, I noticed it is done all with surfaces
rather than solids. Now I've always made pretty much everything in solids,
but seeing this made me think that maybe I'm not doing things the best way.

What advantages are there to working with surfaces over solids( - or visa
versa) ?

Thanks - Sean

 

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.

http://www.deskeng.com/index.php?option=content&task=view&id=501

http://mysite.verizon.net/mjlombard/ follow the "User Groups" link.

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summer so these tutorials are two releases out-of-date, but many of the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.
http://home.pct.edu/~jmather/content/DSG322/SolidWorks_surface_tutorials.htm

 

'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!

 

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

 

Why?

 

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."

 

Sort of like surfaces having two sides?

Solids are bounded by surfaces.
Are they dark inside?

We had those "specific meanings" long ago bounding
things with surfaces only, AFAIK.

Sort of like the inside & the outside?

We had all sorts of such tools back in the days of CADDS IV &
CADS III, among others.

Not really. They just make some things easier for some
designers.
Perhaps your real goal is just a bit of paper?

/ end bait <G>

 

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.

 

Don't even ask about billet <G>.
Or if only the oversized dowls are oversized.

 

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 shit 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... <G>

--Mitch

 

<GAK !!>

 

Tessellation has come a long way Cliff.

 

It's still Tessellation, John.
Once you get there it's hard to get back.
Noise, truncation, approximation, scale, and
rounding have all been added but the parent
computational geometry may have fled.
Not to mention the growth in file size &
complexity and the needed vastly increased
comput power.

Remember: This stuff could all be done in
APT in the 1950s ... on machines of that
era. 16 KB of memory was HUGE even into
the mid 1960s.
As for clock speeds ..... anyone remember what they were?
One source on the IBM 1620 (1965 ?) says "Clock speed: 0.1MHz (10
µs). Peak FLOPS: 300K"