Try

difference () {
cube([3,60,60]);

translate([-0.005,30,30])
rotate([0,90,0])
cylinder(r=15,h=3.01);
}

You need to think about boundaries.

My $0.02 contribution,
Jean-Paul
AC9GH

This is a well known problem, which I think is caused by OpenSCAD using
floating point transformation matrices.

Try this as a workaround:

epsilon = 0.01;

difference () {

cube([3,60,60]);

translate([-epsilon,30,30])

rotate([0,90,0])

  cylinder(r=15,h=3+2*epsilon);

}

On 3 July 2015 at 08:22, easycure easycure@easycure.fr wrote:

You expect the end faces of the rotated cylinder to exactly match up with
the faces of the cuboid, but they don't match due to floating point
roundoff in the rotate. So you include a fudge factor, "epsilon", make the
cylinder slightly taller than 3mm, and make sure the cylinder sticks out
past the cuboid faces on both sides.

On 3 July 2015 at 08:55, easycure easycure@easycure.fr wrote:

Rotation is done internally using trigonometry. In order for the original
code to work, it would be necessary for sin(90) == 1 and cos(90) == 0. In
the version of OpenSCAD I'm using, cos(90) != 0, so your model doesn't work
as expected.

On 3 July 2015 at 09:02, doug moen doug@moens.org wrote:

On 07/03/2015 02:57 PM, doug moen wrote:

It's just dependent on how the graphics driver does the actual
display. I'm getting this even for

difference() {
cube(10, center = true);
cylinder(h = 10, r = 4, center = true);
}

No transformation involved at all, just the difference painting
triangles of different color in one plane.

See https://en.wikipedia.org/wiki/Z-fighting

ciao,
Torsten.

Hi Torsten. You are reporting an F5 bug, whereas I was analyzing an F6 bug.
I think they are two different issues. I can reproduce both.
I think Easycure was also using F6, since his problem goes away with no
rotation.

On 3 July 2015 at 14:59, Torsten Paul Torsten.Paul@gmx.de wrote:

On 07/03/2015 10:28 PM, doug moen wrote:

Right, there was never said what to look at exactly, so I stopped
at the first issue I saw.

Hmm, there's code trying to handle sin() and cos() special cases but
that's not active for rotation(). I guess it's worth a try to catch
those too.

ciao,
Torsten.