Newbie with rotation problem
All I want to do is have a cube with all corners intersecting the axis, thus,
it needs to be rotated. Rotating it 45 degrees like this should work, I
thought: rotate([45, 45, 45]) cube(20, center=true);
But it doesn't! I don't know why but the corners of the cube are not located
on any of the axis. Seems so simple to me, yet I can't understand why it's
not working...
So, question! How do I rotate a cube so all corners will be at one of the
three axis?
With kind regards,
Wim,
W.A. ten Brink.
With kind regards,
Wim,
W.A. ten Brink
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I don't think it is geometrically possible for a cube to do this. A cube
has 12 vertexes, and you want 8 of those vertexes to be aligned with the
axes. It's not possible without warping the cube into an irregular
hexahedron. You can do this with an octahedron, which has 8 vertexes.
On 31 March 2016 at 19:47, Wim ten Brink openscad@wimtenbrink.nl wrote:
All I want to do is have a cube with all corners intersecting the axis,
thus,
it needs to be rotated. Rotating it 45 degrees like this should work, I
thought: rotate([45, 45, 45]) cube(20, center=true);
But it doesn't! I don't know why but the corners of the cube are not
located
on any of the axis. Seems so simple to me, yet I can't understand why it's
not working...
So, question! How do I rotate a cube so all corners will be at one of the
three axis?
With kind regards,
Wim,
W.A. ten Brink.
With kind regards,
Wim,
W.A. ten Brink
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I'm not sure where the 12 vertices comes from, as I count eight, four for the
top face and four for the bottom face, which are common to the sides, of
course.
For the original post, though, I don't believe what you seek is possible.
Consider that if you slice a cube across any plane that meets your
requirements, you do not get a square. I took four points that would
represent two of the axes, but they are not co-planar, so you can't make
them fit on those axes.
A regular octohedron would fit, but would not be a cube, of course. It has
six vertices, to match the axis intersection points.
Wim ten Brink, am I missing something with the vertex counts? They don't
match yours but geometry is challenging me at the moment.
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Okay, dumb question... There are three axis, thus making 6 points where the
cube can go through an axis. But the cube has 8 corners so it will never
touch the axis with all sides...
So, how to create a shape that does have all corners on an axis? Oh, well...
This is what I was actually looking for:
hull(){
translate([10, 0, 0]) sphere(1);
translate([-10, 0, 0]) sphere(1);
translate([0, 10, 0]) sphere(1);
translate([0, -10, 0]) sphere(1);
translate([0, 0, 10]) sphere(1);
translate([0, 0, -10]) sphere(1);
}
Problem solved.
With kind regards,
Wim,
W.A. ten Brink
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Or:
cylinder(r1=10,r2=0,h=10,$fn=4);
scale([1,1,-1]) cylinder(r1=10,r2=0,h=10,$fn=4);
2016-03-31 23:05 GMT-03:00 Wim ten Brink openscad@wimtenbrink.nl:
Okay, dumb question... There are three axis, thus making 6 points where the
cube can go through an axis. But the cube has 8 corners so it will never
touch the axis with all sides...
So, how to create a shape that does have all corners on an axis? Oh,
well...
This is what I was actually looking for:
hull(){
translate([10, 0, 0]) sphere(1);
translate([-10, 0, 0]) sphere(1);
translate([0, 10, 0]) sphere(1);
translate([0, -10, 0]) sphere(1);
translate([0, 0, 10]) sphere(1);
translate([0, 0, -10]) sphere(1);
}
Problem solved.
With kind regards,
Wim,
W.A. ten Brink
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Now that is an interesting use of a negative 'scale' never thought to use it
like that...
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cylinder(r1=10,r2=0,h=10,$fn=4);
mirror([0,0,-1]) cylinder(r1=10,r2=0,h=10,$fn=4);
Is more readable I think.
On 1 April 2016 at 07:02, macdarren macdarren@mac.com wrote:
Now that is an interesting use of a negative 'scale' never thought to use
it
like that...
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Nice! Never considered that option. Normally, I expect round objects with
cylinders. :)
Still like my own, though, since I actually want those rounded edges. But
this is something to remember.
With kind regards,
Wim,
W.A. ten Brink
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Rounded
hull() {
sphere(1);
union() {
cylinder(r1=10,r2=0,h=10,$fn=4);
mirror([0,0,-1]) cylinder(r1=10,r2=0,h=10,$fn=4);
}
}
2016-04-01 5:24 GMT-03:00 Wim ten Brink openscad@wimtenbrink.nl:
Nice! Never considered that option. Normally, I expect round objects with
cylinders. :)
Still like my own, though, since I actually want those rounded edges. But
this is something to remember.
With kind regards,
Wim,
W.A. ten Brink
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Sorry. That is what I mean:
minkowski() {
sphere(1);
union() {
cylinder(r1=10,r2=0,h=10,$fn=4);
mirror([0,0,-1]) cylinder(r1=10,r2=0,h=10,$fn=4);
}
}
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huh...that last doesn't work for me at all...I can kinda round part of the
primary object if I translate the sphere out to the coroner of the object
but still it only rounds part of it...
I admit I don't know much about full, so maybe there is some way to make it
work over the entire thing.
To my mind I would need a sphere at each vertex.
maybe minkowski() instead of hull()?
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On 01. april 2016 21:11, Ronaldo wrote:
Sorry. That is what I mean:
minkowski() {
sphere(1);
union() {
cylinder(r1=10,r2=0,h=10,$fn=4);
mirror([0,0,-1]) cylinder(r1=10,r2=0,h=10,$fn=4);
}
}
Interesting ... so minkowski does not really care about the
specification of the object type (cylinder), only the discretized result.
It appears to me to be a major hack to use cylinder to specify a cone
which becomes a pyramid and then use minkowski on that....
Carsten Arnholm
There are no true spheres, cylinders, circles or curves in OpenScad once
the renderings starts. All the geometry is represented by polygons and
polyhedra.
On 1 April 2016 at 20:45, Carsten Arnholm arnholm@arnholm.org wrote:
On 01. april 2016 21:11, Ronaldo wrote:
Sorry. That is what I mean:
minkowski() {
sphere(1);
union() {
cylinder(r1=10,r2=0,h=10,$fn=4);
mirror([0,0,-1]) cylinder(r1=10,r2=0,h=10,$fn=4);
}
}
Interesting ... so minkowski does not really care about the specification
of the object type (cylinder), only the discretized result.
It appears to me to be a major hack to use cylinder to specify a cone
which becomes a pyramid and then use minkowski on that....
Carsten Arnholm
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I generally use $fn=100; as the first line in my projects, setting it at a
global level. With hull(), it then gives a nice, round shape. The minkowski
version also gives a good-looking result but when I subtract them from one
another by using:
$fn=100;
radius=10;
difference(){
hull(){
translate([radius-1, 0, 0]) sphere(1);
translate([-radius-1, 0, 0]) sphere(1);
translate([0, radius-1, 0]) sphere(1);
translate([0, -radius-1, 0]) sphere(1);
translate([0, 0, radius-1]) sphere(1);
translate([0, 0, -radius-1]) sphere(1);
}
minkowski() {
sphere(1);
union() {
cylinder(r1=radius, r2=0, h=radius, $fn=4);
mirror([0,0,-1]) cylinder(r1=radius, r2=0, h=radius, $fn=4);
}
}
}
Then it seems the minkowski version is a bit wrong. The hull version touches
the axes at exactly 10 but the minkowski is too long on the negative sides.
Thus, the minkowski version doesn't seem to have the same length sides.
(The hull version needs radius-1 because the spheres also take space, and
they have a radius of 1. Total makes the exact radius.
With kind regards,
Wim,
W.A. ten Brink
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Oops, one minus needs to be a +. :)
With kind regards,
Wim,
W.A. ten Brink
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nophead wrote
There are no true spheres, cylinders, circles or curves in OpenScad once
the renderings starts. All the geometry is represented by polygons and
polyhedra.
This is a quiz :) The following image is the preview of translated
primitives. No boolean operations, no rotation, neither scale nor mirror.
How to get them?
http://forum.openscad.org/file/n16907/primitives.png
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It would appear that a good part of the answer to your question lies here:
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids
Some of the answer involves low values of $fn along with cylinders of
different r1 and r2 values.
Do you already know the answers and this is a true quiz, or are you seeking
a solution?
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The second from the left is a sphere.
All the rest could be done using cylinder.
The middle could be a cube.
The second from right could be a sphere.
See how OpenSCAD has warped me? When I first started using OpenSCAD, I was
really annoyed by all of this. I wanted sphere to always produce a sphere,
cylinder to always produce a cylinder, etc.
I am still in favour of adding prism(), pyramid() and cone(), even though
you would normally do those using cylinder().
On 2 April 2016 at 14:21, Ronaldo rcmpersiano@gmail.com wrote:
nophead wrote
There are no true spheres, cylinders, circles or curves in OpenScad once
the renderings starts. All the geometry is represented by polygons and
polyhedra.
This is a quiz :) The following image is the preview of translated
primitives. No boolean operations, no rotation, neither scale nor mirror.
How to get them?
http://forum.openscad.org/file/n16907/primitives.png
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On Sat, Apr 02, 2016 at 02:57:39PM -0400, doug moen wrote:
See how OpenSCAD has warped me? When I first started using OpenSCAD, I was
really annoyed by all of this. I wanted sphere to always produce a sphere,
cylinder to always produce a cylinder, etc.
IMHO, it is fine if openscad has to "simplify" cylinders to extruded
polygons. However, in writing code, it would be best to assume that
the implementation reserves the right to use the simplification OR
BETTER.
That means that the triangular prism could suddenly upgrade to a
perfect cylinder if say the output format directly supports cylinders.
But alas, it has become customary to exploit the defects of the
implementation so that now there is no way back.
I am still in favour of adding prism(), pyramid() and cone(), even though
you would normally do those using cylinder().
Those would, be oneliner modules, right? There is a "system" library
now, so it could be added there, right?
Roger.
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The plan was simple, like my brother-in-law Phil. But unlike
Phil, this plan just might work.
fred_dot_u wrote
It would appear that a good part of the answer to your question lies here:
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids
Some of the answer involves low values of $fn along with cylinders of
different r1 and r2 values.
Do you already know the answers and this is a true quiz, or are you
seeking a solution?
You are right. I generated the image so it is really a quiz.
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