Indeed, that performance is really awful.  Turning on the experimental
vertex-object-renderer features helps a lot.  For me, that alone took
preview performance on your model from unusable to sort-of-usable. 
But still...

The first thing is easy.  Repeat this mantra:  use $fn only to create
regular polygons.  To control circle quality, use $fa and $fs.  $fa=2
/ $fs=1 seems like a reasonable setting here.

Also:  screens are high resolution and really show faces.  3D printing
much less so.  If you turn up your circle quality enough that your
displayed model looks really smooth, you probably have way more faces
than you really need for 3D printing.  Experiment. Note also that you
can set the circle quality to some medium level while you're working,
and to high quality for your final render.

But that still leaves the preview performance pretty poor.

That leads us to a second and more difficult mantra:  never do in 3D
what you can do in 2D.

You have the basic shape of the coin being a torus unioned with a
cylinder, with a sphere subtracted.  But that's the same as a circle
unioned with a rectangle, with a circle subtracted, all
rotate-extruded.  The shape that would be rotate-extruded is this:

That gets you the body of the coin, without anywhere near as many
nasty 3D operations.  (In particular, it avoids that big sphere with
its thousands and thousands of faces - in your design, it has ~26,000
faces.)

Similarly, you have cutout() being a cylinder with a torus
subtracted.  But that's the same thing as a rectangle with a circle
subtracted, rotate-extruded.  The shape that you are rotate-extruding is:

Also, you have a convexity problem on the linear-extruded text.  A
convexity of four is probably enough, but five is definitely enough.

All that done, the performance gets pretty good.

Here's a preview of your model:

Here's a preview of mine:

Mine is a little lower circle resolution on the outside.  My bet is
that the difference isn't visible in 3D printing, but experiment with
$fs.  Setting $fs=0.5 looks like it's better resolution than yours,
but it gets significantly slower (not so much with the vertex-object
stuff turned on).  Experiment with an actual printer.  (Yours has 28K
facets.  Mine with $fs=1 has 10K; with $fs=0.5 has 23K.)  Here's mine
with $fs=0.5:

On my system (i7-13700), yours F6-renders in 1m6s; mine with $fs=1
renders in 15s; with $fs=0.5 in 54s.  But with the experimental
Manifold renderer, they're all sub-second.  (Manifold is magic.)

If one wanted to optimize further, note that cutout() is a fully
cylindrical object, and only a small fraction of it is actually used
for the subtraction.  You could use rotate_extrude's angle parameter
to only generate maybe a quarter of it.  Those invisible negative
faces have a preview cost (and probably a rendering cost too).  But
that seems like overkill.

Anyhow, there's some ideas.  Here's my version.

$fa = 2;
$fs = 1;
innendd= 6;
akr=5;
kr=20;
exr = 14;

maker_coin(r=kr, or=akr, innerh=innendd, exd=exr) {
linear_extrude(height=2*akr, convexity=5)
text("OS", size= 10, halign = "center", valign = "center");
}

// r= radius of the coin- outercircle diam, inner height
module maker_coin(r, or, innerh, exd) {
difference() {
maker_coin_body(r=kr, or=akr, innerh=innendd, exd=exd);
translate([0,0,2]) children();
}
}

module maker_coin_body(r, or, innerh, exd) {
resth = 2or-innerh;
bigd = (r^2+resth^2)/resth; //euklidischer Höhensatz·
difference() {
union() {
rotate_extrude() {
difference() {
union() {
square([r, 2or]);
translate([r,or])circle(r=or);
}
translate([0,bigd/2 + innerh]) {
circle(d = bigd);
}
}
}
}
union() {
for(w=[0:360/8:360]) rotate([0,0,w])
translate([r+2*or,0,-.1]) cutout(r=r, or=or, exd=exd);
}
}
}

module cutout(r, or, exd) {
rotate_extrude() {
difference() {
square([0.75exd, 2or + 2]);
cutr = or+0.2;
translate([exd/2+cutr,cutr-0.2])
circle(r=cutr);
}
}
}

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Indeed, that performance is really awful.  Turning on the experimental
vertex-object-renderer features helps a lot.  For me, that alone took
preview performance on your model from unusable to sort-of-usable.  But
still...

The first thing is easy.  Repeat this mantra:  use $fn only to create
regular polygons.  To control circle quality, use $fa and $fs.  $fa=2 /
$fs=1 seems like a reasonable setting here.

That leads us to a second and more difficult mantra:  never do in 3D what
you can do in 2D.

You have the basic shape of the coin being a torus unioned with a
cylinder, with a sphere subtracted.  But that's the same as a circle
unioned with a rectangle, with a circle subtracted, all rotate-extruded.
The shape that would be rotate-extruded is this:

that's also exactly what Angus did :'(

That gets you the body of the coin, without anywhere near as many nasty 3D
operations.  (In particular, it avoids that big sphere with its thousands
and thousands of faces - in your design, it has ~26,000 faces.)

Similarly, you have cutout() being a cylinder with a torus subtracted.
But that's the same thing as a rectangle with a circle subtracted,
rotate-extruded.

Also, you have a convexity problem on the linear-extruded text.  A
convexity of four is probably enough, but five is definitely enough.

in 15s; with $fs=0.5 in 54s.  But with the experimental Manifold renderer,
they're all sub-second.  (Manifold is magic.)

If one wanted to optimize further, note that cutout() is a fully
cylindrical object, and only a small fraction of it is actually used for
the subtraction.  You could use rotate_extrude's angle parameter to only
generate maybe a quarter of it.  Those invisible negative faces have a
preview cost (and probably a rendering cost too).  But that seems like
overkill.

:

Hello all,
will still work on that for

• limiting the cutouts to the necessary angles as Jordan suggested
• and have to somehow add the x/y bevel to the cutouts,

in the meantime, i put it up here:
https://github.com/nohkumado/opensource_makercoin for review,
validation suggestions (i used the images you kindly provided, Jordan,
hope that's ok?), and in a few day i will try to push it onto Angus :D

thanks!

Am Sa., 2. März 2024 um 08:59 Uhr schrieb Bruno Boettcher
bboett@gmail.com:

 Hello Jordan!

 wow... thanks a lots for the very detailed analysis!


 Am Fr., 1. März 2024 um 21:00 Uhr schrieb Jordan Brown
 <openscad@jordan.maileater.net>:

     Indeed, that performance is really awful.  Turning on the
     experimental vertex-object-renderer features helps a lot.  For
     me, that alone took preview performance on your model from
     unusable to sort-of-usable.  But still...

     The first thing is easy.  Repeat this mantra:  use $fn only to
     create regular polygons.  To control circle quality, use $fa
     and $fs.  $fa=2 / $fs=1 seems like a reasonable setting here.

 ok, indeed :D looks bad on the screen but you are right, the
 printer hasn't that good of a resolution....


     That leads us to a second and more difficult mantra: never do
     in 3D what you can do in 2D.

 will try to keep that in mind :D


     You have the basic shape of the coin being a torus unioned
     with a cylinder, with a sphere subtracted. But that's the same
     as a circle unioned with a rectangle, with a circle
     subtracted, all rotate-extruded.  The shape that would be
     rotate-extruded is this:

 that's also exactly what Angus did :'(


     That gets you the body of the coin, without anywhere near as
     many nasty 3D operations.  (In particular, it avoids that big
     sphere with its thousands and thousands of faces - in your
     design, it has ~26,000 faces.)

 ok, think i get it.....


     Similarly, you have cutout() being a cylinder with a torus
     subtracted.  But that's the same thing as a rectangle with a
     circle subtracted, rotate-extruded.

 hmmm since we are at it... a hint how to integrate directly also
 the horizontal bevels to that shape?



     Also, you have a convexity problem on the linear-extruded
     text.  A convexity of four is probably enough, but five is
     definitely enough.

 oh.... never looked into convexity, but noticed the ugly artifacts...

     On my system (i7-13700), yours F6-renders in 1m6s; mine with
     $fs=1 renders in 15s; with $fs=0.5 in 54s. But with the
     experimental Manifold renderer, they're all sub-second. 
     (Manifold is magic.)

 my system is definitely slower :D but nevermind, your version
 clearly is the one to go with! thanks!



     If one wanted to optimize further, note that cutout() is a
     fully cylindrical object, and only a small fraction of it is
     actually used for the subtraction. You could use
     rotate_extrude's angle parameter to only generate maybe a
     quarter of it.  Those invisible negative faces have a preview
     cost (and probably a rendering cost too).  But that seems like
     overkill.

 nope, will look into that! seems logical..
 but as said i still need to add also in x/y plane the bevel, and
 not really knowing how to achieve that....

 anyway thanks a lot, i will put this up later on github, for
 further enhancements and review!
 thanks a lot!

 -- 
 ciao
 Bruno

 

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http://bboett.free.frhttp://aikido.nohkumado.eu/,
http://bboett.free.fr
http://aikido.zorn.free.fr

--
ciao
Bruno

---==========
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nope, will look into that! seems logical..