<p>From your observations it is assumed that you expected a hollow donut where the &quot;current blind hole&quot; would extrude through the shell of the donut. Please <a href="https://3dprinting.stackexchange.com/posts/23438/edit">update your question</a> if this isn't the case.</p>
<p>3D modelling programs are solid modeling design programs where solid objects are created, usually from extruding 2D shapes. You revolve a scaled 2D circle around the Z-axis to get the solid donut shape. Although the hole is a blind hole, and you would expect the slicer to cut the hole through the surcafe when you are not using infill, the blind hole is part of the outer surface of the object; the slicer renders the wall of the complete surface, including the wall of the hole. Whether you remove the infill does not change that! If you need it to be hollow, you need to create a pocket in the the object.</p>
<p>For a hollow donut, you need to extract the inner core from the donut:</p>
<pre><code><span class="math-container">$fn = $</span>preview ? 90 : 360;
toroH3=30;
toroD3=38;
toroL3=20;

difference(){
  // Body
  rotate_extrude(convexity = 10)
    translate([toroD3, (toroH3/2), 0])
      resize([toroL3,toroH3,0])
        circle(d = toroD3);
  // Extract inner core of the body
  rotate_extrude(convexity = 10)
    translate([toroD3, (toroH3/2), 0])
      resize([toroL3-2,toroH3-2,0])
        circle(d = toroD3);
  // Cut hole in the body
  translate([0,47.2,9])
    rotate([74,0,0])
      cylinder(2,2,2);
  // Cutout to view inside
  if ($preview) {
    // Cut if in Preview (F5), not in Render (F6)
    cube(50);
  }
}
</code></pre>
<p>With &quot;F5&quot; you get a cutout view of the donut to see it is empty:
<a href="https://i.sstatic.net/4vvO7sLj.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/4vvO7sLj.png" alt="enter image description here" /></a></p>
<p>With &quot;F6&quot; you get the perfectly rendered version with the hole in the shell:
<a href="https://i.sstatic.net/JpPGZiS2.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/JpPGZiS2.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2024-07-10T16:30:08.343Z
I added an image from the Slicer, as you can see the donut  is hollow as I use no filling, but the hole on the surface is closed on the inside. I will like to have the same as I see on the cad.. a donut with a hole on the side :)
Paolol
CC BY-SA 4.0
2024-07-10T19:05:03.243Z
@Paolol Yes, the hole is a blind hole in the slicer as is renders the wall of the complete surface, including the wall of the hole. Whether you remove the infill does not change that! If you need it to be hollow, you need to follow the strategy in the answer.
0scar
CC BY-SA 4.0
2024-07-11T06:37:28.673Z
Thanks a lot for you time and to explain me the problem :)
Paolol
CC BY-SA 4.0
2024-07-11T13:40:42.777Z
@Paolol No problem, I'll update the answer with the text in the comment!
0scar
CC BY-SA 4.0
2024-07-09T14:28:23.190Z
2024-07-11T13:45:03.873Z
2024-07-11T13:45:03.873Z
0scar
<p>Hi I made a donut with a hole on the external side, but when I slice it the internal side of the cylinder is closed, this resul in a closed-hole.I will be glad if any one can explain me  where is the problem.</p>
<pre><code>$fn = 100;
toroH3=30;
toroD3=38;
toroL3=20;

difference(){
  rotate_extrude(convexity = 10)
    translate([toroD3, (toroH3/2), 0])
      resize([toroL3,toroH3,0])
        circle(d = toroD3, $fn = 100);
  translate([0,47.2,9])
    rotate([74,0,0])
      cylinder(2,2,2);
}
</code></pre>
<p>Added slicer image
<a href="https://i.sstatic.net/3K2f34sl.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/3K2f34sl.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2024-07-08T21:41:51.377Z
Could you add images of what the problem is? I've rendered the code and I see a donut with a blind hole in it and is slices perfectly, I do see a blind hole. What do you expect? The cutout of the hole is by use of a short cylinder; did you want to create the hole throught the donut? I'm guessing you where aiming for an empty donut?
0scar
<openscad>
OpenSCAD hole is closed on the inside when in slicer
Paolol
# OpenSCAD hole is closed on the inside when in slicer

(Asked by: username_0 on 2024-07-08)

Hi I made a donut with a hole on the external side, but when I slice it the internal side of the cylinder is closed, this resul in a closed-hole.I will be glad if any one can explain me  where is the problem.
$fn = 100;
toroH3=30;
toroD3=38;
toroL3=20;

difference(){
  rotate_extrude(convexity = 10)
    translate([toroD3, (toroH3/2), 0])
      resize([toroL3,toroH3,0])
        circle(d = toroD3, $fn = 100);
  translate([0,47.2,9])
    rotate([74,0,0])
      cylinder(2,2,2);
}

Added slicer image

**Tags:** openscad
> **Comments:**
> **username_1**: Could you add images of what the problem is? I've rendered the code and I see a donut with a blind hole in it and is slices perfectly, I do see a blind hole. What do you expect? The cutout of the hole is by use of a short cylinder; did you want to create the hole throught the donut? I'm guessing you where aiming for an empty donut?  

---

## 1 answers

### Answer by username_1 on 2024-07-09. Score: 1 | Accepted answer

From your observations it is assumed that you expected a hollow donut where the "current blind hole" would extrude through the shell of the donut. Please update your question if this isn't the case.
3D modelling programs are solid modeling design programs where solid objects are created, usually from extruding 2D shapes. You revolve a scaled 2D circle around the Z-axis to get the solid donut shape. Although the hole is a blind hole, and you would expect the slicer to cut the hole through the surcafe when you are not using infill, the blind hole is part of the outer surface of the object; the slicer renders the wall of the complete surface, including the wall of the hole. Whether you remove the infill does not change that! If you need it to be hollow, you need to create a pocket in the the object.
For a hollow donut, you need to extract the inner core from the donut:
$fn = $preview ? 90 : 360;
toroH3=30;
toroD3=38;
toroL3=20;

difference(){
  // Body
  rotate_extrude(convexity = 10)
    translate([toroD3, (toroH3/2), 0])
      resize([toroL3,toroH3,0])
        circle(d = toroD3);
  // Extract inner core of the body
  rotate_extrude(convexity = 10)
    translate([toroD3, (toroH3/2), 0])
      resize([toroL3-2,toroH3-2,0])
        circle(d = toroD3);
  // Cut hole in the body
  translate([0,47.2,9])
    rotate([74,0,0])
      cylinder(2,2,2);
  // Cutout to view inside
  if ($preview) {
    // Cut if in Preview (F5), not in Render (F6)
    cube(50);
  }
}

With "F5" you get a cutout view of the donut to see it is empty:

With "F6" you get the perfectly rendered version with the hole in the shell:

> **Comments:**
> **username_0**: I added an image from the Slicer, as you can see the donut  is hollow as I use no filling, but the hole on the surface is closed on the inside. I will like to have the same as I see on the cad.. a donut with a hole on the side :)  
> **username_1**: @Paolol Yes, the hole is a blind hole in the slicer as is renders the wall of the complete surface, including the wall of the hole. Whether you remove the infill does not change that! If you need it to be hollow, you need to follow the strategy in the answer.  
> **username_0**: Thanks a lot for you time and to explain me the problem :)  
> **username_1**: @Paolol No problem, I'll update the answer with the text in the comment!  

---

