Take the hull of a very thin cylinder and a square to form the outer shape.
Subtract a smaller but slightly longer version to make it hollow.

On Thu, 8 Jul 2021 at 17:52, Frank Paynter paynterf@gmail.com wrote:

If you want an option that is more curved, without the triangular faces on
the side you can look at

https://github.com/revarbat/BOSL2/wiki/skin.scad#functionmodule-skin

Examples 11 and 12.

On Thu, Jul 8, 2021 at 1:04 PM nop head nop.head@gmail.com wrote:

On 08.07.2021 18:52, Frank Paynter wrote:

Well, you might be able to write one based on this AngelCAD script. See
the STL included there for the result.

https://gist.github.com/arnholm/b798d062ab914eb19dffce751ed86427

Carsten Arholm

On Thu, Jul 08, 2021 at 12:52:04PM -0400, Frank Paynter wrote:

Yup. 3 minutes work:

dcyl = 40;
dsqu = 40;

wt = 2;

hh = 40;

module cylsqu (ds, dcy, hh)
{
dh = .5;
hull () {
cylinder (d=ds, h=dh, $fn=4);
translate ([0,0,hh-dh]) cylinder (d=dcy, h=dh, $fn=60);
}
}

module hcylsqu (ds, dcy, hh)
{
difference () {
cylsqu (dsqu+2wt, dcyl+2wt, hh);
translate ([0,0,-0.01]) cylsqu (dsqu, dcyl, hh+.02);

}
}

hcylsqu (dsqu, dcyl, hh);

Adapting from "square" as implemented to "rectangle" is left as an
excercise for the reader.

Roger. 

--
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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.

Wow!  I'm in love with hull()!!  Thanks Roger!!

Yup. 3 minutes work:

dcyl = 40;
dsqu = 40;

wt = 2;

hh = 40;

module cylsqu (ds, dcy, hh)
{
dh = .5;
hull () {
cylinder (d=ds, h=dh, $fn=4);
translate ([0,0,hh-dh]) cylinder (d=dcy, h=dh, $fn=60);
}
}

module hcylsqu (ds, dcy, hh)
{
difference () {
cylsqu (dsqu+2wt, dcyl+2wt, hh);
translate ([0,0,-0.01]) cylsqu (dsqu, dcyl, hh+.02);

}
}

hcylsqu (dsqu, dcyl, hh);

Adapting from "square" as implemented to "rectangle" is left as an
excercise for the reader.

    Roger.

On Thu, Jul 8, 2021 at 12:52 PM Frank Paynter paynterf@gmail.com wrote:

--
G.Frank Paynter, PhD
OSU ESL Research Scientist (ret)
EM Workbench LLC
614 638-6749 (cell)