Assuming I have:

translate([4, 5, 0])
cylinder(d1=10, d2=0, h=10);

cylinder(d1=10, d2=0, h=10);

translate([-5, 3, 0])
cylinder(d1=15, d2=0, h=10);

The result is this:

http://forum.openscad.org/file/t2594/example_01.png

This is just a simple example. I need to be able to split this up into
chunks for 3d printing. (It's for an art project)

Right now, I'm doing 160x160 mm regions (via intersection with cube).

However, this leaves very very ugly inorganic seams.

I would like to be able to do basically "intersections between cones
extruded along z axis", for lack of a better term.

Where two of the cones intersect, I would like to be able to "cut straight
down" to the xy plane.

The result for this example would be three separate objects, that get
"cylinderified" at the points where they intersect.

Does this make sense? I can provide a pencil sketch if that would be helpful
also.

This must be possible, I just am not skilled enough with openscad to achieve
this.

My thought is perhaps create 2d profile shapes from the intersection of the
cones, projected to an xy plane at z = 0. Then extrude those above the cone
max heights. Finally, one by one, do intersections of those extruded
projections with each cone. I'm not exactly sure how to do this though.

(In addition, what is the name of the operation I am trying to accomplish
here?)

Thank you so much!!

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It will get tedious for more numerous objects.
There is probably some algorithm from set theory out there to help...

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I think MIchael's code can be simplified by:

module cutCyl() {
difference()
{
children(0);
for(i=[1:1:$children-1])
linear_extrude(height=1000)
projection() children(i);
}
}

cutCyl() { c1(); c2(); c3();} };

However, the union of that last object with c2() and c3() does not seem to
be the intended split of the cone union.

[image: CutCones.PNG]

The problem as I see is that the line of intersection of two cones is in a
vertical plane just in the very specific case where both cone have same
height and base diameter. In those case, a vertical plane can "organically"
split the twp cones.

I think now I have understood guaranteed_interwoven's construction. Very
clever split.

$fn = 20;

t1 = [4, 5, 0];
t2 = [0, 0, 0];
t3 = [-5, 3, 0];
delta = 0.02;

module c1() translate(t1) cylinder(d1=10, d2=0, h=10);
module c2() translate(t2) cylinder(d1=10, d2=0, h=10);
module c3() translate(t3) cylinder(d1=15, d2=0, h=10);

module cutCyl()
intersection() {
children(0);
linear_extrude(height=1000)
projection()
difference() {
children(0);
for(i=[1:1:$children-1]) children(i);
}
}

translate(deltat1) cutCyl() { c1(); c2(); c3();}
translate(deltat2) cutCyl() { c2(); c1(); c3();}
translate(delta*t3) cutCyl() { c3(); c1(); c2();}

[image: CutCones.PNG]

You folks are my heroes :)

This last one is exactly what I needed! Especially with the delta in there,
that is very slick.

In terms of iterating over each object and exporting, I have been using bash
for that, so no worries there. (Unless there is a better way I'm not aware
of.)

This is perfect! Thank you so much!!

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Sent from: http://forum.openscad.org/

My apologies, one last question here.

I'm trying to do one last generifying step, to extend to an arbitrary number
of objects.

$fn = 20;

module gen_node(coords, d, h)
{
translate(coords)
cylinder(d1=d, d2=0, h=h);
}

module cutCyl()
{
intersection()
{
children(0);
linear_extrude(height=1000)
projection()
{
difference()
{
children(0);
for(i=[1:1:$children-1]) children(i);
}
}
}
}

data = [
[[4, 5, 0], 10, 10],
[[0, 0, 0], 10, 20],
[[-5, 3, 0], 15, 10],
[[-2, 6, 0], 15, 7],
];

/* Does not work:
cutCyl()
{
for (i = [0: len(data)])
{
gen_node(data[i][0], data[i][1], data[i][2], data[i][3]);
}
}
*/

// Does work
cutCyl()
{
gen_node(data[0][0], data[0][1], data[0][2], data[0][3]);
gen_node(data[1][0], data[1][1], data[1][2], data[1][3]);
gen_node(data[2][0], data[2][1], data[2][2], data[2][3]);
gen_node(data[3][0], data[3][1], data[3][2], data[3][3]);
}

I did notice that the delta doesn't work for certain shapes. The delta is a
good idea I think to guarantee that the pieces fit together once printed.
What I can do is that the "subtracting" objects can just have their
diameters increased by that delta, which I think will work nicely.

So I basically want to do a for loop from within cutCyl, but the actual for
loop version doesn't work. I had a suspicion that the for loop was affecting
the object tree, but I'm not exactly sure how. So I tried to unroll the for
loop manually, and this does work.

So my question is now "How do I modify cutCyl so that it can accept the for
looped version here?"

(As an aside, I have been writing openscad code the same way I am used to
writing C, with the opening braces on the next line. However, I defer to the
style guide of the language of course, is this generally frowned upon?
Should I adopt the style I have seen in examples in this thread?)

Thank you!!

--
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for() has an implicit union() so only returns one object.
So children() doesn't see each iteration if the for().

Admin - email* me if you need anything, or if I've done something stupid...

• click on my MichaelAtOz label, there is a link to email me.

Unless specifically shown otherwise above, my contribution is in the Public Domain; to the extent possible under law, I have waived all copyright and related or neighbouring rights to this work. Obviously inclusion of works of previous authors is not included in the above.

The TPP is no simple “trade agreement.”  Fight it! http://www.ourfairdeal.org/  time is running out!

Sent from: http://forum.openscad.org/