Hi!

Openscad has problems deciding if the planes exist or not since you're subtracting a cylinder of the same height from the original one.

Change the translate to ([25,0,-1])
and the subtracted cylinder to (r=30, h=14)

Now the render will have no issues.

It'll render faster, too...

Trygve

Den 24. juli 2022 kl. 23.44.22 +02.00 skrev Julien Jacquet jacquetjulien@gmail.com:

Ok the problem is the floating point values, thanks

Le dim. 24 juil. 2022 à 23:59, Jordan Brown openscad@jordan.maileater.net
a écrit :

Julien:

It is not that simple.  The two surfaces are in the exact same place,
floating point or not.  And in the case of OpenSCAD, I believe that
coordinates are not stored as floating point

Jon

On 7/24/2022 6:13 PM, Julien Jacquet wrote:

On 7/24/2022 3:13 PM, Julien Jacquet wrote:

Eh, not really.

You'll see this behavior with simple integer cases.

difference() {
    cube(2);
    cube(1);
}

The problem is not unique to OpenSCAD.  See
https://en.wikipedia.org/wiki/Z-fighting for a generic discussion.

I fix this by including a "zff = 0.001;", for "Z-Fight Fudge", constant at
the top of my files. When the z-fighting in the previous is particularly
troublesome I can use zff to make something slightly taller, or shorter, or
moved slightly, to eliminate the ambiguity of which face is closer to the
camera. The value is too small to cause any dimensional problems for the
things I work on, but it can be set back to 0 for exporting if you're
paranoid.

On Mon, 25 Jul 2022 at 08:35, Jordan Brown openscad@jordan.maileater.net
wrote:

On Sun, Jul 24, 2022 at 03:34:58PM -0700, Jordan Brown wrote:

What /is/ unique to openscad is that it happens with stuff that is
invisble.

Hmm. My example now doesn't do it:

cube (10);

difference () {
cube ([20,9,8]);
translate ([-5,5,5]) cube ([30,5,5]);
}

In more complex cases I see it happening when the object that is
subtracted from something else conincides with a plane of something
visible.

Roger. 

--
** R.E.Wolff@BitWizard.nl ** https://www.BitWizard.nl/ ** +31-15-2049110 **
**    Delftechpark 11 2628 XJ  Delft, The Netherlands.  KVK: 27239233    **
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.

Ok, thank you to all the people who responded, all your input was helpful.
I like the idea of the variable at the beginning of the program with a
small epsilon
Julien

Le lun. 25 juil. 2022 à 06:54, Rogier Wolff R.E.Wolff@bitwizard.nl a
écrit :