I could be wrong about any/all of this, but if you want to rotate around a
non origin axis, I would stay you should translate the object away from the
origin and then rotate as normal. The effect this has is equal to what you
want and gives you complete control. With 6 degrees of freedom (trans x y
z, rot xy,yz, zx) you should be able to accomplish any possible 3D affine
transformation.

Now using this strategy to make good designs can be tricky, and depending
on exactly what you want might be the wrong approach. Say you want a bolt
hole pattern, but you need the holes to be square (if they were cylindrical
the rotation wouldn't matter)  then you would need to rotate them around an
axis outside of their shape. wrap this in a for loop to make say 10 holes a
fixed radius from the origin.

radius =5;
for(i=[0:10]){
rotate([0,0,i*(360/10)]){
translate([radius, 0,0]){
cube([1,1,1]);
}}}

As an experiment, what happens if you switch the rotate and translate
statements order? Then they evaluate in the opposite way and you should be
left with a star shape.

On Wed, Oct 30, 2019 at 3:38 PM Robin2 robin@nbleopard.com wrote:

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Matt Maggio
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mmaggio wrote

Thanks.

I'm aware that I can do that. My question is whether it is possible just
using the rotate() command - in other words, maybe I have missed a feature
of the rotate() command.

...R

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

The builtin rotate module can rotate about any vector which goes
through the origin.  If you want to pivot around something not on the
origin, then you'll have to do additional translations.

Here is a "one-liner" module to do it for you.  just specify the pivot point p.

module rotate_about(a, v, p=[0,0,0]) {
translate(p) rotate(a,v) translate(-p) children();
}

-Hans

On Thu, Oct 31, 2019 at 4:48 PM adrianv avm4@cornell.edu wrote:

thehans wrote

Thanks. That's how it had seemed to me. I had been hoping I was missing
something because for the use-case I have in mind it would be very
inconvenient to use a translate()

It will be easier to make a roughly equivalent 2D drawing in LibreOffice and
experiment with the motion in it.

...R

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

Geogebra.org is a very useful tool for trying motions.
I once used it to determine how a string length varied going around multiple pulleys in a joined arm, as the arm moved.
Dave

--
David Gustavson
dbg@SCIzzL.com

On Fri, Nov 1, 2019, at 9:28 AM, Robin2 wrote:

lar3ry wrote

Many thanks but the need is not sufficient to justify that much effort :)

...R

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