How do you do something like Radiate Surface - but in 3d?

You know what radiate surface looks like? It basically offsets edges by
a specified amount and then creates a surface between outer and inner
edges/sketches. But it does something that offset doesn't/can't do - it
deals wonderfully with splines. Try and create a body with some faces
containing splines and then offseting all faces - sometimes it will
work and sometimes it won't - due to minimum curvature or similar
problems.

Radiate always works by somehow dealing with those issues. Is there
something that will do radiate but in 3 dimensions rather than just 2?
I.e. offset a set of surfaces by a specified amount and if it
encounters problems with spline faces deal with them like radiate does
rather than just giving up due to minimum curvature or somesuch?

Thanks in advance.

If you know how to do it with API even better!

P.s. yes I know I can use scale but scale doesn't really offset
surfaces and I need surfaces to be offset by a certain amount.

 

It would be so much easier to explain if I could post a picture of what
problems I'm having and what I'd like to do...

 

So why don't you take a screen shot and upload your pic on ImageShack
(http://imageshack.us) and then post a link.

Muggs

 

doh!

ok here's the first image that shows trying to offset surfaces (and
failing)
http://img182.imageshack.us/img182/3716/untitled1copyxv1.jpg

the second image shows why it failed
http://img477.imageshack.us/img477/4426/untitled2copypi5.jpg

and the third image shows what I would want it to do
http://img477.imageshack.us/img477/4227/untitled3copyrr1.jpg

I've even tried Offset Entities in a sketch but that messes up on
splines as well.

I hope it's a bit clearer now. So like in picture 3 but in all 3
dimensions, not just 2. Thank you!

 

Look into "Ruled Surface" feature. I think it will do what you need.

 

nope, that doesn't do what I need. think offset surface, but "better",
as in "radiate surface" kind of better.

 

The curvature being pointed to in the third image isn't why it's
failing. What you point to is an outside radius and when offset is
getting bigger. Failures are caused by the radius offsetting smaller
past zero. I would be willing to bet the failure has to do with that
feather edge to the right of the arrow. When SW has to offset a very
shallow angle, it has to extend edges, and when it extends spline edges,
they get unpredictable and may not intersect the other side. In the
first image, you can see the offset faces are almost parallel in that
area, and the extension to make them intersect is going to be long. In
the second image, you make a little arc out of the edge which is great,
but SW won't do that for you automatically.

Also, its not clear at all where the 3D curvature in your part is or
what you are wanting to do in 3D. You shouldn't be so fast to dismiss
Ruled surface functions, they are the improvement on radiate.

 

I suspect that this is not the part you are actually trying to offset
surfaces from. If it were, then the solution would be a piece of cake -
use radiate (or ruled surface - at the core they are the same thing),
convert the outer edge, extrude, and you have the offset surface you
want.

The reason that offset surface doesn't always work on more complicated
samples is something you probably know intuitively from your experience
mowing your lawn.
When you mow your lawn, you are in essence offsetting the perimeter of
your lawn with each pass of the lawnmower. At first you have a single
curve around the perimeter, but with each pass the inside corners get
tighter and the outside corners get rounder. At some point, the inital
smooth curve on the inside corners turns into a sharp corner - offset
surfaces (and shells - same thing when you get down to it) have to deal
with that when the minimum radius of curvature on an inside curve
exceeds the shell/offset distance.
That is why the minimum radius of curvature tool is only partly useful
- if that minimum radius is an 'outside curve' it gets bigger and
bigger and becomes less of a problem as the offset/shell thickness
becomes larger. The only minimum radius of curvature you have to worry
about are inside curves (for instance, rounds instead of fillets).

In general. SWx isn't as smart as you are when you mow your lawn. It
doesn't generally like to split a single face into two faces (the sharp
corner you create with your lawn mower after a few passes around an
inside curve). However, SHELL has had some special exceptions coded
into it that will allow this sort of thing to happen - often
accompanied by a yellow exclamation point on the SHELL feature that
won't go away (see part two of my Curvy Stuff presentations at last
years SWx World - at www.dimontegroup.com)

To get through this, sometimes we have to take the bull by the horns.

In the sample you showed, you could offset those faces that you can,
then use your superior brain to make the faces that SWx CAN'T figure
out itself and trim them together. Its not fun, but it gets the job
done. Just last week I had to build multiple shells on a job by hand -
its actually quite easy when you get the hang of it (same goes with
offset surfaces - after all, shells are just offset surfaces). There
are also samples of that on my website from old SWx World
presentations, though I don't give any warranty for those old files
working in the current SWx. However, the principle is still valid -
offset what you can, make what you can't.

Ed

BTW - radiated surfaces are ruled surfaces, and are simple - just
imagine the spines sticking out of a porcupine. That's what a ruled
surface is - a bunch of spines sticking out of the porcupine that get
linked toeghether into a single surface .I am not sure how SWx deals
with the spines sticking out from an inside curve where they would
overlap - that's kind of cool, but it is a 2D (sort of) problem.
Turning it into a 3D problem (offset surface) is wayyyy more
complicated and currently seems to take a human intelligence to solve -
that's why we make them ourselves.

 

I'll try and describe what I'm trying to do. Look at the preview in the
first picture. That's what offset faces would do and that's what I'm
trying to achieve - i.e. offset all faces by 3mm. But offset fails
because of the face pointed to by the arrow. Yes it's to do with the
inside radius on one of the points on the spline getting past 0 where
the spline begins to intersect with itself. Now what I'd want it to do
is following: if a face is going to fail because of that then create a
face that follows the edge as created per radiate surface.

 

I have gone through your presentation about the yard problem and it
pretty much hit the nail on the head but only in 2D. How to do
something like that in 3D? I have thought of intersecting the model
with several planes in all 3 dimensions, doing a radiate on the
resulting edges/faces but then the geometry doesn't line up at all.

 

Here is another set of images to help you visualise what I'm after

First image shows the starting body
http://img82.imageshack.us/img82/6918/untitled1copybf8.jpg

Second image shows the resulting body
http://img132.imageshack.us/img132/4058/untitled2copyfi2.jpg

And the third image shows the differences (original body highlighted in
green)
http://img82.imageshack.us/img82/6899/untitled3copyay1.jpg

Clearer now?

 

What I guess I didn't convey very well is that the problem exists in
every 2D section through a 3D surface. Take an angled slice, parallel
slices, kattywompass slices - in every slice, it still applies. The
net of all those slices is your 3D surface. Just like the point of
every spine on the porcupine makes a 3D shape, even when those spines
overlap or intertwine. Porcupines can do this easily - SW, not so
much.

Fortunately, every sample you've posted is a simple planar problem.
Paul's post works, but again because it was a simple planar problem.
The important thing to note is that even in a simple planar problem the
route to a solution is to build the offset ssrface yourself (like Paul
did by converting the edge of the radiated surface and extruding it).
You can do this in 3D when necessary, usually throuhg more
construction, but it can be done and a lot of times it takes less time
than you would ever suspect. Usually, you only have to make a patch or
two. My rule is offset what you can, build what you must.

To your point, why can't SWx figure it out? I dunno. I lack the math
skills - its pretty complex stuff.
I just know from years of building plastic models as a kid that the
inside was often sort of 'muddy' or 'soft' looking, where the toolmaker
couldn't make a pure offset of the outside (presumably with a
pantograph) so they just sort of filled in material (by grinding away
the tool walls manually) while keeping that wall section as consistent
as possible. They did it by hand, I do it by hand (my hand, of course,
on a mouse).