Hi Bob,

I did discover that the problem appears only when the rounding is exactly 1/2 the thickness.  Changing the rounding to T/2=.01 made the hole visible.  Is there anything else (a parameter or such) that can also fix it?

Thanks

Bob

Saturday, July 20, 2024, 9:08:01 PM, you wrote:

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

Bob, what I found is, you need to make the cylinder slightly longer that
the thickness of the part it is cutting, otherwise it doesn't show up
properly on an f5.

include <BOSL2/std.scad> //or screws or threading
$fn=24;

difference(){
       cuboid([10,10,2],anchor=LEFT+FRONT+BOTTOM);
     translate([5,5,-0.5])  cyl(r=2,h=3,anchor=BOTTOM);
}

right(11)difference(){
       cuboid([10,10,2],anchor=LEFT+FRONT+BOTTOM,rounding=1);
     translate([5,5,-1])  cyl(r=2,h=4,anchor=BOTTOM);
}

On 2024-07-21 11:15, Bob Roos via Discuss wrote:

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Hi Ken,

I actually tried that, but with anchor=BOTTOM or TOP the taller will not penetrate both sides..  I would put the thickness as T+1 and it would cut through the top side and leave the bottom fulled in.
 
Ah Ha! you translated the holes downward.  I was concerned about keeping thing even, but holes don't generate any material so they can be non co planar with the other objects.
 
Something tells tht this is not a solution for all cases, but I don't know specifics ATM
 
Bob

Saturday, July 20, 2024, 9:29:26 PM, you wrote:

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

A couple of tricks here.

when subtracting a cylinder from another object, the cylinder can be
anything more than the size of the object it's going through. It can be
1mm, 10mm, or 1000mm longer than the object, all that counts is the
intersection.

For cutting holes in an object, I generally (and easily) use a cylinder
2, 3 or 4 times longer, and then translate it by 1/2, or 1 times the
length of the cylinder.

Hint for aligning parts:  when doing a difference()

put it completely on one line so it can be commented out.  The resulting
{} structure is valid.  Making the cylinders long enough allows you to
see where the holes are, and then trim the position if you need to.

when aligned, allow the difference() to be uncommented.

Harvey

On 7/21/2024 12:45 AM, Bob Roos via Discuss wrote:

Another way to "comment out" a statement is to put a "*" in front of
that statement.  This disables the statement, which can be many lines long.

Jon

On 7/21/2024 10:30 AM, Harvey white via Discuss wrote:

...

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I generally use notepad++ as the editor which allows highlighting a
block and then commenting it out completely.  it can be used with syntax
highlighting for a user defined language for OpenSCAD.

Harvey

On 7/21/2024 10:37 AM, Jon Bondy via Discuss wrote:

The problem is that when the intersecting object's wall having the same plane as the side of the intersected object, OpenSCAD doesn't know if there's a 'zero thickness' wall there or not.
And while it might look right on the final render, odds are that there's a heap of 'zero thickness' artifacts there.

So make certain the intersecting object starts before, and ends after the intersected object if it's to go all the way through.

Trygve

Den 21. juli 2024 kl. 03.08.01 +02.00 skrev Bob Roos via Discuss discuss@lists.openscad.org:

I think the simplest and cleanest way to do this is like this, with hole
cutting cylinders CENTERED on the parent object and no fussy translate
needed.

include <BOSL2/std.scad> //or screws or threading
$fn=24;

diff(){
cuboid([10,10,2],anchor=LEFT+FRONT+BOTTOM)
tag("remove") cyl(r=2,h=3);
}

right(11)diff(){
cuboid([10,10,2],anchor=LEFT+FRONT+BOTTOM,rounding=1)
tag("remove") cyl(r=2,h=3);
}

On Sun, Jul 21, 2024 at 10:52 AM Harvey white via Discuss <
discuss@lists.openscad.org> wrote:

On Sat, Jul 20, 2024 at 09:08:01PM -0400, Bob Roos via Discuss wrote:

In the old days the overlapping top and bottom surfaces of the
cylinder and cube would be guaranteed to lead to problems. The program
would be uncertain if passing that surface of the cube and subtracted
cylinder at the same time would put you inside the remaining solid or
not.

Nowadays openscad is a lot better, you can often get away with doing
this. Apparently you've found a case where you can't.

I always do stuff like:

ch = 3;
difference () {
cube ([10,10,ch]);
translate (5,5,-1]) cylinder (d=3, h=ch+2);
}

that the subtracted object is always sticking out a little bit. .01mm
is enough, but nowadays I often just use 1mm.

Roger. 

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