I'm building a vacuum manifold of sorts. It's clearly a vacuum device, as it
will be connected to my shop vac. It probably is a manifold, as it will
"distribute" the vacuum from the hose to the edge of a US sized 1x2 piece of
lumber with holes drilled in suitable locations.

http://forum.openscad.org/file/n17894/vacuum_manifold.png

As this will be printed on a 3d printer, I'd like to do without
3d-printer-related supports as much as possible. No supports is my primary
goal. I believe the design as presented would print well enough, once I
taper the hose cylinder at the top. Its bottom edge is a horizontal surface,
but doesn't have to be and I should be able to "difference-cone" a taper
that will preclude the need of printer-related support in that area. When
sliced, those particular supports extend the entire height and would be a
pain to remove.

On to the crux of the biscuit.

Because my shop vac really sucks, I expect that the walls would be prone to
collapse, perhaps to destruction. I plan to add a single layer of
light-weight fiberglass and epoxy resin to make the structure air-tight and
perhaps improve the strength, but internal structural supports would
certainly improve my chances.

Even though I am what I consider a sloppy code-writer, having no real
training in this practice, I've learned to generate reasonably clean
understandable code for this model. Everything is as parametric as I can get
it and I'd like to keep it that way.

The model is constructed by generating a flat plane base of appropriate
dimensions at z = 0 and a second cross-section at the correct height to
clear the obstacle created by the device for this this is being built. Using
hull() provides a clean transition and a pleasing shape, in my opinion. I've
confirmed the clearance by adding an intermediate "bulkhead" of the
obstruction and the resulting shape is within that bulkhead, so it's been
removed from the code and can be considered insignificant.

The hollow interior is generated in a similar manner. Using reduced size
bulkheads in the same locations, the hull() shape is differenced from the
primary shape. I'm satisfied with the result and wish to build on that.

I have to consider that the printer will be placing layers in the
orientation shown in the model, and avoid bridging. It's acceptable to have
vanes extending upward from z = 0 with reasonable spacing along the y axis,
but I've been unable to create code in my alleged mind that will limit the
height of the vanes to allow airflow bypass as the vanes near the upper
edge.

The difference() portion could be used as a sub-foundation, I believe,
removing material from that module. Everywhere something is removed would
result in something being generated within the manifold. Even with that in
mind, I'm unable to create suitable shapes to prevent bridging or the need
for 3d-printer-support structures.

I expect that some may consider the above code to be simplistic, but I don't
handle the complex options of loops and the like that are available within
OpenSCAD. Perhaps that's why I'm unable to create a concept for internal
printable structural supports.

The supports could be ordinary posts, but would have to have tapers or
curvature in the vertical direction in order to avoid the printer-generated
support aspect. If the supports are vanes, I'd like to have a graduated
taper of the profile as they near the apex of the model. That is to say, the
vanes in the center should be farther away from the top edge of the model,
allowing for more air to reach the outer vanes, which will have gradually
reduced gaps from the top edge of the model, relative to the horizontal
position of the vanes.

I've been able to create a base of baffles:

http://forum.openscad.org/file/n17894/baffles.png

It's not much, almost nothing and I run into a bind when I try to limit the
extension. I realized later during this project that the baffles also do not
get larger in the y direction in order to encompass the manifold y increase
as it "climbs" toward the cylinder at the top.

baffles option has the best chance. It's also possible that if someone can
help me understand the algorithms or concepts involved in making the baffles
work, I might be able to understand the method needed to create tapered
posts within the manifold.

I'm hopeful that the code gurus on the list will be able to point me in the
right direction. If it's possible to not-write the code for me, that would
be great. I may be too dense to have that aspect work, however.

thanks
fred

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If I understand your problem well, you are interested to keep the walls
distanced by guide vanes, that don't disturb the airflow. The key approach
to add vanes into a complex hollow shape is to difference them from the
interior before you difference the interior from the primary shape. See
this code example:

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