On Wed, Mar 16, 2022 at 08:03:54AM -0400, jon wrote:

module CubeCXY(v) translate([-v[0]/2, -v[1]/2, 0]) cube (v);

--
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f equals m times a. When your f is steady, and your m is going down
your a is going up.  -- Chris Hadfield about flying up the space shuttle.

too simple and straightforward...

a bit more involved

module cubec(x,y,z)
{
    scale ([x,y,z])
    rotate([0,0,45])
    linear_extrude(1)
    circle (sqrt(2)/2,$fn=4);
}

cubec(80,40,50);

On 16/03/2022 12:32, Rogier Wolff wrote:

LOL!  Yes!  So many ways to approach this simple construct!

On 3/16/2022 10:07 AM, Raymond West wrote:

On 3/15/2022 9:26 PM, David Schooley wrote:

My point is that by default they all start at Z=0 and expand into +Z
from there, which helps me to think of the bottom as the "first" face.

But I agree that it would be good to have more options.  One of my
library modules is jcube(), which builds a cube and then justifies it as
specified by a vec3.  In each axis, -1 justifies the cube on the
negative side of the origin, 0 centers, and +1 justifies on the positive
side.  Thus, for instance, jcube(dims=[1,1,1], j=[0,0,-1]) makes a cube
that is centered in X and Y, and extends down from the origin in Z.  I
use jcube() all the time; it makes things significantly simpler. 
There's been some discussion of having the standard center argument take
a similar vec3, but it's never gone anywhere.

I also have a more general justify() that accepts a bounding box for its
children and a justification parameter, and justifies its children.

I've been thinking about a jcircle(), but that's trickier because you
have to decide whether you want to align based on a theoretical circle,
or on the actual polygon generated.  They're only the same for $fn being
a multiple of four.  (And it's worse for spheres, where there's no $fn
that puts vertices on all three axes.)

Not good to have the outer dimensions multiples of an irrational even when
the cube is aligned with the axes and it has rational dimensions.

I override sphere() to have points on all six half axes by making it a
rotate_extrude of a semi circle. Otherwise anything created with hulls of
spheres has incorrect dimensions.

On Wed, 16 Mar 2022 at 14:49, jon jon@jonbondy.com wrote:

Just curious, how do you make the semicircle?

On Wed, Mar 16, 2022, 10:14 nop head nop.head@gmail.com wrote:

function r2sides(r) = $fn ? $fn : ceil(max(min(360/ $fa, r * 2 * PI / $fs),
5));    //! Replicates the OpenSCAD logic to calculate the number of sides
from the radius
function r2sides4n(r) = floor((r2sides(r) + 3) / 4) * 4;
//! Round up the number of sides to a multiple of 4 to ensure
points land on all axes

module circle4n(r, d = undef) {                    //! Circle with
multiple of 4 vertices
R = is_undef(d) ? r : d / 2;
circle(R, $fn = r2sides4n(R));
}

module semi_circle(r, d = undef)                    //! A semi circle in
the positive Y domain
intersection() {
R = is_undef(d) ? r : d / 2;
circle4n(R);

    sq = R + 1;
    translate([-sq, 0])
        square([2 * sq, sq]);
}

//! Redefines sphere() to always have a vertex on all six half axes I.e.
vertices at the poles and the equator and $fn a multiple of four.
//! This ensures hull and minkowski results have the correct dimensions
when spheres are placed at the corners.

module sphere(r = 1, d = undef) {                  //! Override sphere
so that has vertices on all three axes. Has the advantage of giving correct
dimensions when hulled
R = is_undef(d) ? r : d / 2;
rotate_extrude($fn = r2sides4n(R))
rotate(-90)
semi_circle(R);
}

On Wed, 16 Mar 2022 at 15:16, Leonard Martin Struttmann <
lenstruttmann@gmail.com> wrote:

There is of course the BOSL2 solution, which provides similar flexibility, e.g.

cube(10, anchor=[0,0,-1]);  // cube with center of bottom face at the origin
cube(10,anchor=BOTTOM); // equivalent to above
cube(10,anchor=[1,1,0]);  // cube with its (1,1) vertical edge
centered on the origin
cube(10,anchor=BACK+RIGHT);  // equivalent to above

And so on.

On Wed, Mar 16, 2022 at 11:09 AM Jordan Brown
openscad@jordan.maileater.net wrote:

On 3/16/2022 11:16 AM, Leonard Martin Struttmann wrote:

Just for fun, here's one way to do that:

projection() rotate_extrude(angle=180) square([10,0.001]); //
semicircle, radius 10, in positive y

Thank you! TIL...

I'm not sure how I managed to avoid knowing that, but thank you. That
will come in handy.

On 3/16/2022 8:19 AM, Torsten Paul wrote: