Your question is not clearly posed.  Do you mean this?

include<BOSL2/std.scad>
size = 20;
$fa=1;$fs=.3;
diff()
cuboid(size)
attach(TOP,TOP,inside=true)
cyl(h=size,d=4,rounding=-2,extra=1);  // extra adds length to avoid
z-fighting

[image: image.png]

On Fri, Jun 6, 2025 at 4:33 PM Joe Weinpert via Discuss <
discuss@lists.openscad.org> wrote:

If the hole is circular, and the object it penetrates has flat sides
that are perpendicular to the hole axis, then a simple solution is to
create a square, centred on the origin, and at each corner difference a
circle the radius being the radius of your rounding and centred on each
corner. Then rotate_extrude that with an offset of the radius of your
hole. Subtract that shape from the solid at the ends of the hole.

On 06/06/2025 21:32, Joe Weinpert via Discuss wrote:

Hi Adrian,

You're right, I could have phrased my question more clearly! But yes, the
solution you provided is exactly what I was trying to achieve. Thanks so
much for that!

I have a follow-up question. What if the hole isn't cylindrical but has an
irregular shape defined by a list of points? Would it still be possible to
add a radius to the top and bottom edges of such a hole?

Thanks again for your help!

On Fri, Jun 6, 2025 at 6:10 PM Adrian Mariano via Discuss <
discuss@lists.openscad.org> wrote:

Adrian, when I run this code snippet, it produces the cube with the hole and rounding in it, but I get the error "Warning: variable "extra" not specified as parameter", and of course there is no lengthening of the cylinder to stop the z-fighting. Try as I might, I can find no examples of the use of extra anywhere, so can you explain what is wrong please?
If I can get this working, it will be very useful.

On 2025-06-07 08:09, Adrian Mariano via Discuss wrote:

--
Cheers, Ken
bats059@gmail.com
https://vk7krj.com
https://vk7krj.com/running.html

A baby can be defined as an ego with a noise at one end and a smell at the other.
Your job as parents is to teach them to control all three.
My job as a grandad is to tell you how you are doing it all wrong!

Problem solved Adrian- my Bosl2 was out-of-date. Downloaded the latest from github, extra now works as advertised- thanks🙂

On 2025-06-07 08:09, Adrian Mariano via Discuss wrote:

--
Cheers, Ken
bats059@gmail.com
https://vk7krj.com
https://vk7krj.com/running.html

A baby can be defined as an ego with a noise at one end and a smell at the other.
Your job as parents is to teach them to control all three.
My job as a grandad is to tell you how you are doing it all wrong!

Like I said -

// rounded hole demo

block = 50;  // size of demo cube
rad = 4;       // radius of rounding
diam = 20;      // diameter of hole

$fn=200;
module plain(){
 difference(){
   cube(50,true);
     translate([0,0,-(block+20)/2])
     cylinder(d=diam,h=block+20);
 }
}

//plain();

module prof(){
  difference(){
    square(rad*2,true);
     translate([rad,rad])circle(r=rad);
     translate([rad,-rad])circle(r=rad);
     translate([-rad,rad])circle(r=rad);
     translate([-rad,-rad])circle(r=rad);
 }
}

//prof();

module round(){
 rotate_extrude(){
 translate([diam/2,0,0])prof();
 }
}

//round();

module doit(){
  difference(){
    plain();
     translate([0,0,block/2])round();
     translate([0,0,-block/2])round();
  }
}

doit();

On 06/06/2025 23:12, Raymond West via Discuss wrote:

Yes, you can do the same thing using an irregular shaped hole.  If your
hole is polygonal, or is a polygon with rounded corners, then you can use
rounded_prism to make the hole.  If your hole has lots of points (e.g. it's
a continuous shape) then join_prism is best.  The API for join_prism is
hard to use, though may be not terrible for this case of a vertical hole.
I wrote a better API in prism_coinnector().

A polygon hole (with rounded corners) using rounded_prism:

include<BOSL2/std.scad>
include<BOSL2/rounding.scad>  // Not needed with recent versions
size = 20;
M = path3d(turtle(["left", 180, "length",3,"move", "left", "move", 3,
"right",
"move", "right", "move", 4, "right", "move", 3, "right",
"move", 2]));
fudge = .01;
diff()
cuboid(size)
attach(TOP,TOP,inside=true)
down(fudge/2)
rounded_prism(M, up(size+fudge,M), joint_sides=1, joint_top=-2,
joint_bot=-2);

Note that if you don't like the attachment stuff you can discard it and
just use difference() with the rounded_prism() call and position the cutout
where you need manually.

[image: image.png]

When the hole has a rounded shape, that is, described by many points, with
curves, then use prism_connector or join_prism:

include<BOSL2/std.scad>
include<BOSL2/rounding.scad>  // Not needed with recent versions

flower = [for(theta=lerpn(0,360,180,endpoint=false))
(15+1.3sin(6theta))*[cos(theta),sin(theta)]];
size = 20;
fudge = .01;
diff()
cuboid(size)
tag("remove")prism_connector(scale(.4,flower), parent(), TOP,
parent(), BOT, fillet=2);

Here if you don't like the attachment stuff you have to use join_prism()
instead.

[image: image.png]

On Fri, Jun 6, 2025 at 7:08 PM Joe Weinpert via Discuss <
discuss@lists.openscad.org> wrote:

On Sat, 2025-06-07 at 21:42 +1000, Ken via Discuss wrote:

I had the same problem, except that 'inside' gave the same error. I
downloaded the latest version from github, using 'Download ZIP', but I
still get the error, and thr flared hole appears on top of the cube.

Larry, is it possible that your code is not finding the updated version?
That's the only explanation I can come up with.

On Sat, Jun 7, 2025 at 1:41 PM larry via Discuss discuss@lists.openscad.org
wrote: