Hello !

In a software I'm developping, I'm trying to use OpenSCAD to generate a 3D
model of one of the parts that the software is computing.

The thing I'm trying to make is usually a big cylinder with a lot of holes
in it (can range from around a hundred holes to a few thousand).

So naively, I did the following to generate it :

• 1 : draw the "big" cylinder.
• 2 : draw every hole has a tiny cylinder with the same height has the
  big one.
• 3 : Use difference() with the big cylinder and all the tiny cylinder.

So something like this in OpenSCAD (I've attached an exemple of what my
software generate) :

difference() {
cylinder(1.000000,400.000000,400.000000,true);
union() {
translate([0.000000,0.000000,0.000000]) {
cylinder(1.000000,6.500000,6.500000,true); }
translate([31.180000,0.000000,0.000000]) {
cylinder(1.000000,6.500000,6.500000,true); }
translate([-31.180000,0.000000,0.000000]) {
cylinde(1.000000,6.500000,6.500000,true); }
translate([62.350000,0.000000,0.000000]) {
cylinder(1.000000,6.500000,6.500000,true); }
.......
}
}

My problem is that, even though the preview works great, when trying to
render the mesh, it can take around half an hour to an hour and a half to
complete, even with a fairly powerful PC and with the last version of
OpenSCAD (2016.01.27).
I tried to tweak around using $fn, $fa and $fs, but the rendering time is
still very long.

So, I was wondering if my method was completly wrong or if there was any
advice you could give me to lower the rendering time.

Faithfully yours,

Maël Naccache contact@maeln.com
Président de l'association Rally Point : rallypoint.fr

OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org

It will be much faster if you do it in 2D with circles and then
linear_extrude it to make the cylinder.

In a few tests I tried, the rendering time is almost one third when
the hole cylinders have a height greater than the base one. Anyway,
avoiding coincident faces in CSG operations is a good practice.

Hello,

You may try something like this:

//parametric code

DefaultSides=16;
nLines=10;
nCols=50;
hPitch=10;
vPitch=10;
Dout=6;
Din=0;
Sides=24;
cHeight=1;
tHeight=cHeight+2;
Angl=360;
cRad = (nLines <= nCols)? (nColshPitch+4hPitch)/2 :
(nLinesvPitch+4vPitch)/2;

module Tube(Length,Dout,Din,Sides,Angl)  // render(convexity=4)
{
NSides= (Sides < 3 || Sides==undef)  ?  DefaultSides : Sides;
rotate_extrude( angle=Angl, convexity=4, $fn=NSides )
translate([Din/2,0,0])
square([(Dout-Din)/2,Length]);
}

module MultiTubes()
{
for (i=[0:nLines-1]){
for (j=[0:nCols-1]){
shift=ceil(j/2)-floor(j/2);
translate([jhPitch,ivPitch+shift*(hPitch/2),cHeight/2-1])
Tube(tHeight,Dout,Din,Sides,Angl);
}
}
}

//MultiTubes();

module PerfuratedCylinder() render(convexity=10)
{
difference(){
translate([(nCols-1)*hPitch/2,(nLines-1)*vPitch/2, cHeight/2])
cylinder(h=cHeight, r=cRad, $fn=48);
MultiTubes();
}
}
PerfuratedCylinder();

//end code

Cheers
jpmendes

Using circle make it way faster, but when I do
the linear_extrude,
it take nearly the same amount of time has my previous method :/ .

Do you have a more complete example of your code that takes a long
time? I may want to experiment. Is it just a question of subtracting a
lot of small cylinders from a large one?

Carsten Arnholm

I've attached two exemple that takes a long time to render.

Yep, that's just it, I want to substract a lot of small cylinders (who
share the same size) from a big one.

I found circle_extrude1.scad to be instantaneous for F6 in
OpenScad2015.05.16 (git e673fff) .

Total rendering time: 0 hours, 0 minutes, 0 seconds

Top level object is a 3D object:

Facets: 59016

The reason is it doesn't use GCAL for 2D or linear extrude.

​

Are you using an old version of OpenScad? It used to use GCAL for 2D.