It's interesting to see how other people think and approach 3D design.

Here's my take on the same model.  Obviously, our minds take different
routes to the same destination.

include <LMS/AssemblyStandard.scad>

// internal dimensions (clearance for A7 paper =11080, A6= 153110
length = 80;
width = 110;
height = 25;  // total height (external)
thick = 1.8;
gap = 20; //gap at corner
rad = 20; // corner radius

$fn=80;

module roundedCutout()
{
difference()
{
cube( [ 2rad, 2rad, height ] );

translate( [ 0, 0, -E ] )
cylinder( h=height+2*E, r=rad );

}
}

module box()
{
difference()
{
cube( [ length+2thick, width+2thick, height ] );

translate( [ thick, thick, thick ] )
cube( [ length, width, height ] );

translate( [ length-rad, -E, thick ] )
cube( [ rad+2*thick+E, rad+E, height ] );

translate( [ length-rad+2*thick, rad, 0-E ] )
rotate( [ 0, 0, -90 ] )
roundedCutout();

translate( [ length-2*rad, 0.5*rad, height-rad ] )
rotate( [ 90, 0, 0 ] )
roundedCutout();

translate( [ 2*height+length-2*rad, 2*rad, height-rad ] )
rotate( [ 90, 0, -90 ] )
roundedCutout();

}
}

box();

On Wed, Jun 22, 2022 at 12:45 PM zipang@tethys.re wrote:

Oh, and I forgot:

E  = 0.2;  //  Defined in the included file

On Wed, Jun 22, 2022 at 1:26 PM Leonard Martin Struttmann <
lenstruttmann@gmail.com> wrote:

Hi Leonard,

Why are the 2 F5 renderings so different?  This one show up with a solid object with no "holes" and the previous version has "holes" depending on how it is oriented.
 
Also the interior is green but on the first it is all yellow.
 
Sorry but I don't have a way to show images at the moment.
 
Bob Roos

Wednesday, June 22, 2022, 2:26:41 PM, you wrote:

-- 
have Fun,
 Bob                           mailto:roosbob@wybatap.com

1. As for the "holes" that show up in the preview, I do not know.  It may
   have something to do with the way that Raymond created his cut outs.  Try
   View -> Thrown Together to see all of the shapes used to create the cut
   outs.

2. As for the color, Raymond's box is all yellow since he created it with a
   single linear_extrude.  Mine shows green since my box is created by
   subtracting one box from another bigger box.

There are many people here on the list who are much smarter than me and who
can probably explain these things better.  :-)

On Wed, Jun 22, 2022 at 2:54 PM Bob Roos roosbob@wybatap.com wrote:

On 6/22/2022 12:54 PM, Bob Roos wrote:

Classic convexity artifacts.

  linear_extrude(height, convexity=2){

fixes it, though I usually set it to 10 or so to be safe.  (There's
basically no cost for a model this simple.  You have to have a very
complex model before there starts to be a real cost.)

Spaces on the sides of a subtracted-away object default to green.

On 6/22/2022 2:48 PM, Jordan Brown wrote:

https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem#Extrude_parameters_for_all_extrusion_modes
(Also applies to import, polyhedron, and a few others.)

Consider this simplified version of the key part of the model:

length = 80;
width = 110;
thick = 1.8;
gap = 20; //gap at corner

difference(){
    offset(thick)
        square([length,width]);
    square([length,width]);
    translate([length-gap,-2*thick])
        square(gap+(2*thick));
}

color("red")  translate([-20,0,0]) rotate(45)cube([170,2,2]);

Note that the red line crosses the figure twice.

If we linear extrude that figure without specifying convexity, and
difference away a little bit, we get this artifact-y view:

Basically, any sight line where the number of crossings is greater than
the specified convexity gets displayed wrong.

Here's another simple example to play with.

difference() {
linear_extrude(height=10) {
square(10);
translate([5,5]) square(10);
}
cube(1);
}

(Also shows classic Z-fighting artifacts around the 1x1x1 cube
subtracted at the origin.)

On 22/06/2022 19:26, Leonard Martin Struttmann wrote:

generally, I take one cube from another to make a box, but offset is
simple to round corners. I originally had the gap as a relationship to
the width and length, but found it better to control it manually, so to
speak, as often it needs to be about an inch or so, whatever size box.
Also the corner and edge radius sort of relates to height and gap, so
again, manual selection, with the advantage you can have a solid corner,
if needed. Openscad is great for simple mechanical designs. Of course,
with the correct/incorrect values, you can sort of blow it up. Too much
to think about if wanting to validate the values, it is simpler to see
what it looks like.

Thanks for the comments.

I would compose a box from linear extrudes of 2D differences rather than do
a 3D difference as it is much faster.

On Wed, 22 Jun 2022 at 23:14, Raymond West raywest@raywest.com wrote: