Bevelling a cylinder creates a void

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Bevelling a cylinder creates a void

lleblanc
I'm trying to bevel a drilled cylinder, but I when I do that, the top
of the cylinder disappears into a (green) hole. I attached a
screenshot. The 3D printer-owning friend I sent my STL to says there's
a strange gap at the top.

$fn=100;

difference()
{
    difference()
    {
        cylinder(h=39, d=13.69);

         // bevel
        translate([-6.845,-15,18])
        {
            rotate(a=[0,-56.89,0])
            {
                cube(30);
            }
        }
    }

    // bolt hole
    cylinder(h=39, d=4);
}

Of course, if I remove the bevel, the top of the cylinder is normal (yellow).

Is this a bug? Is there a better way to bevel a cylinder?


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Re: Bevelling a cylinder creates a void

adrianv
The model works for me.   What version of OpenSCAD are you using?  


lleblanc wrote

> I'm trying to bevel a drilled cylinder, but I when I do that, the top
> of the cylinder disappears into a (green) hole. I attached a
> screenshot. The 3D printer-owning friend I sent my STL to says there's
> a strange gap at the top.
>
> $fn=100;
>
> difference()
> {
>     difference()
>     {
>         cylinder(h=39, d=13.69);
>
>          // bevel
>         translate([-6.845,-15,18])
>         {
>             rotate(a=[0,-56.89,0])
>             {
>                 cube(30);
>             }
>         }
>     }
>
>     // bolt hole
>     cylinder(h=39, d=4);
> }
>
> Of course, if I remove the bevel, the top of the cylinder is normal
> (yellow).
>
> Is this a bug? Is there a better way to bevel a cylinder?
>
>
> --
> Luc Le Blanc
>
> _______________________________________________
> OpenSCAD mailing list

> Discuss@.openscad

> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>
>
> bevel.png (9K)
> <http://forum.openscad.org/attachment/31592/0/bevel.png>





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Re: Bevelling a cylinder creates a void

OpenSCAD mailing list-2
When I run your code on my machine (Win7, OpenSCAD 2019.05) everything is fine. The exported STL passes Meshmixer inspector (watertight/manifold) and would likely print fine.

On Saturday, January 16, 2021, 11:58:40 AM EST, adrianv <[hidden email]> wrote:


The model works for me.  What version of OpenSCAD are you using? 


lleblanc wrote

> I'm trying to bevel a drilled cylinder, but I when I do that, the top
> of the cylinder disappears into a (green) hole. I attached a
> screenshot. The 3D printer-owning friend I sent my STL to says there's
> a strange gap at the top.
>
> $fn=100;
>
> difference()
> {
>    difference()
>    {
>        cylinder(h=39, d=13.69);
>
>          // bevel
>        translate([-6.845,-15,18])
>        {
>            rotate(a=[0,-56.89,0])
>            {
>                cube(30);
>            }
>        }
>    }
>
>    // bolt hole
>    cylinder(h=39, d=4);
> }
>
> Of course, if I remove the bevel, the top of the cylinder is normal
> (yellow).
>
> Is this a bug? Is there a better way to bevel a cylinder?
>
>
> --
> Luc Le Blanc
>
> _______________________________________________
> OpenSCAD mailing list

> [hidden email]

> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>
>
> bevel.png (9K)
> &lt;<a shape="rect" href="http://forum.openscad.org/attachment/31592/0/bevel.png>" target="_blank">http://forum.openscad.org/attachment/31592/0/bevel.png>





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Re: Bevelling a cylinder creates a void

caggius
I tried playing with the code and I get some rather strange F5 previews but the F6  render is OK using  2021.01.13 (git 0f79135ef) 

    difference(){      
        linear_extrude(39){
            difference(){   
                circle(d=13.69);
                circle(d=4);
            }    
        }
        // bevel
        translate([13.69/2,0,39]) rotate([0,-56.89,0]) cylinder(d=60,h=15);      
   }





On 16 Jan 2021, at 17:03, fred via Discuss <[hidden email]> wrote:

When I run your code on my machine (Win7, OpenSCAD 2019.05) everything is fine. The exported STL passes Meshmixer inspector (watertight/manifold) and would likely print fine.

On Saturday, January 16, 2021, 11:58:40 AM EST, adrianv <[hidden email]> wrote:


The model works for me.  What version of OpenSCAD are you using? 


lleblanc wrote

> I'm trying to bevel a drilled cylinder, but I when I do that, the top
> of the cylinder disappears into a (green) hole. I attached a
> screenshot. The 3D printer-owning friend I sent my STL to says there's
> a strange gap at the top.
>
> $fn=100;
>
> difference()
> {
>    difference()
>    {
>        cylinder(h=39, d=13.69);
>
>          // bevel
>        translate([-6.845,-15,18])
>        {
>            rotate(a=[0,-56.89,0])
>            {
>                cube(30);
>            }
>        }
>    }
>
>    // bolt hole
>    cylinder(h=39, d=4);
> }
>
> Of course, if I remove the bevel, the top of the cylinder is normal
> (yellow).
>
> Is this a bug? Is there a better way to bevel a cylinder?
>
>
> --
> Luc Le Blanc
>
> _______________________________________________
> OpenSCAD mailing list

> [hidden email]

> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>
>
> bevel.png (9K)
> &lt;http://forum.openscad.org/attachment/31592/0/bevel.png>





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Re: Bevelling a cylinder creates a void

mondo
In reply to this post by lleblanc

I find that when subtracting shapes, you need to make them longer than what you are subtracting the shape from. If both edges are on the same plane, it often has no idea what to do, you can see the flashing yellow/green of indecision...

On 16/01/2021 16:35, Luc Le
On 16/01/2021 16:35, Luc Le Blanc wrote:
I'm trying to bevel a drilled cylinder, but I when I do that, the top
of the cylinder disappears into a (green) hole. I attached a
screenshot. The 3D printer-owning friend I sent my STL to says there's
a strange gap at the top.

$fn=100;

difference()
{
    difference()
    {
        cylinder(h=39, d=13.69);

         // bevel
        translate([-6.845,-15,18])
        {
            rotate(a=[0,-56.89,0])
            {
                cube(30);
            }
        }
    }

    // bolt hole
    cylinder(h=39, d=4);
}

Of course, if I remove the bevel, the top of the cylinder is normal (yellow).

Is this a bug? Is there a better way to bevel a cylinder?



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Re: Bevelling a cylinder creates a void

mondo
In reply to this post by lleblanc
make the last line -

   translate([0,0,-2]) cylinder(h=40, d=4);

On 16/01/2021 16:35, Luc Le Blanc wrote:

> $fn=100;
>
> difference()
> {
>      difference()
>      {
>          cylinder(h=39, d=13.69);
>
>           // bevel
>          translate([-6.845,-15,18])
>          {
>              rotate(a=[0,-56.89,0])
>              {
>                  cube(30);
>              }
>          }
>      }
>
>      // bolt hole
>      cylinder(h=39, d=4);
> }

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Re: Bevelling a cylinder creates a void

adrianv
In reply to this post by caggius
I get weird behavior like that with the 2019.05 version as well as the RC5
version.   It also persists if I shrink the cutting cylinder down to a
smaller diameter.   I've seen weird preview behavior when the cutting object
is really big (like bigger than the viewport) but not in a case like this,
that I can remember.

It's bizarre that it works fine if you do the difference() in 3d but gives
those weird results when you use the more efficient technique of doing the
difference in 2d.  

One other remark to the original poster:  When you do a difference it's
normal for the cut surface to be green.  


I tried playing with the code and I get some rather strange F5 previews but
the F6  render is OK using  2021.01.13 (git 0f79135ef)

    difference(){      
        linear_extrude(39){
            difference(){  
                circle(d=13.69);
                circle(d=4);
            }    
        }
        // bevel
        translate([13.69/2,0,39]) rotate([0,-56.89,0]) cylinder(d=60,h=15);      
   }








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Re: Bevelling a cylinder creates a void

TLC123
That is  to low convexity, default should be much higher but it is what it is
.

difference(){      
        linear_extrude(39,convexity=10){
            difference(){  
                circle(d=13.69);
                circle(d=4);
            }    
        }
        // bevel
        translate([13.69/2,0,39]) rotate([0,-56.89,0]) cylinder(d=60,h=15);      
   }



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Re: Bevelling a cylinder creates a void

adrianv
I never remember convexity.  I have it set to 10 in all my library functions,
and I've never noticed that this causes any problems or performance issues.
Is there some reason the default couldn't be changed in a future version of
OpenSCAD?    Why would anybody need convexity to be low?  


TLC123 wrote

> That is  to low convexity, default should be much higher but it is what it
> is
> .
>
> difference(){      
>         linear_extrude(39,convexity=10){
>             difference(){  
>                 circle(d=13.69);
>                 circle(d=4);
>             }    
>         }
>         // bevel
>         translate([13.69/2,0,39]) rotate([0,-56.89,0])
> cylinder(d=60,h=15);      
>    }
>
>
>
> --
> Sent from: http://forum.openscad.org/
>
> _______________________________________________
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> Discuss@.openscad

> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org





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Re: Bevelling a cylinder creates a void

nophead
I think because 1 is the fastest and is correct for all the builtin solids.

Odd thing is that the number required seems to be PC dependent. On an old laptop I had to set it higher!

On Sat, 16 Jan 2021 at 18:29, adrianv <[hidden email]> wrote:
I never remember convexity.  I have it set to 10 in all my library functions,
and I've never noticed that this causes any problems or performance issues.
Is there some reason the default couldn't be changed in a future version of
OpenSCAD?    Why would anybody need convexity to be low? 


TLC123 wrote
> That is  to low convexity, default should be much higher but it is what it
> is
> .
>
> difference(){     
>         linear_extrude(39,convexity=10){
>             difference(){ 
>                 circle(d=13.69);
>                 circle(d=4);
>             }   
>         }
>         // bevel
>         translate([13.69/2,0,39]) rotate([0,-56.89,0])
> cylinder(d=60,h=15);     
>    }
>
>
>
> --
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>
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Re: Bevelling a cylinder creates a void

jon_bondy
In reply to this post by adrianv
I suggested this a long time ago

On 1/16/2021 1:28 PM, adrianv wrote:
> I never remember convexity.  I have it set to 10 in all my library functions,
> and I've never noticed that this causes any problems or performance issues.
> Is there some reason the default couldn't be changed in a future version of
> OpenSCAD?    Why would anybody need convexity to be low?
>

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Re: Bevelling a cylinder creates a void

nophead
I wonder if once the vbo rendering gets merged the default can be increased. It is something like two orders of magnitude faster drawing OpenSCG scenes. Will that swamp increasing convexity to 10? I have never been able to perceive a higher convexity actually being slower.

On Sat, 16 Jan 2021 at 18:42, jon <[hidden email]> wrote:
I suggested this a long time ago

On 1/16/2021 1:28 PM, adrianv wrote:
> I never remember convexity.  I have it set to 10 in all my library functions,
> and I've never noticed that this causes any problems or performance issues.
> Is there some reason the default couldn't be changed in a future version of
> OpenSCAD?    Why would anybody need convexity to be low?
>

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Re: Bevelling a cylinder creates a void

adrianv
I did a little experimentation using the beveled cylinder as a test case.  It
appears to display correctly with convexity 2 but wrong with convexity 1.  I
don't notice any difference in performance with convexity 1 vs convexity 10.
With convexity 100 it's still hard to identify a difference.  Maybe a very
slight degradation?  With convexity 1000 the model rotates jerkily and it is
hard to control.  

I increased complexity by making a 10x10 array of beveled cylinders, so 100
objects.  In this case a difference is very clear.  With convexity 1 it
rotates very responsively (with incorrect display).  With 2 it is also
responsive.  With 10 there is a very noticeable lag with jerky
rotation---it's hard to rotate the model.  With 100 it's unusable.  

Note that the time to produce the preview is the same regardless of the
convexity value.    


nophead wrote
> I wonder if once the vbo rendering gets merged the default can be
> increased. It is something like two orders of magnitude faster drawing
> OpenSCG scenes. Will that swamp increasing convexity to 10? I have never
> been able to perceive a higher convexity actually being slower.
>
> On Sat, 16 Jan 2021 at 18:42, jon &lt;

> jon@

> &gt; wrote:
>
>> I suggested this a long time ago
>>
>> On 1/16/2021 1:28 PM, adrianv wrote:
>> > I never remember convexity.  I have it set to 10 in all my library
>> functions,
>> > and I've never noticed that this causes any problems or performance
>> issues.
>> > Is there some reason the default couldn't be changed in a future
>> version
>> of
>> > OpenSCAD?    Why would anybody need convexity to be low?
>> >
>>
>> _______________________________________________
>> OpenSCAD mailing list
>>

> Discuss@.openscad

>> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>>
>
> _______________________________________________
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> Discuss@.openscad

> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org





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Re: Bevelling a cylinder creates a void

jon_bondy
Excellent experiment!   Thank you!

I wonder why it gets jerky if the preview time is always the same

On 1/16/2021 1:55 PM, adrianv wrote:

> I did a little experimentation using the beveled cylinder as a test case.  It
> appears to display correctly with convexity 2 but wrong with convexity 1.  I
> don't notice any difference in performance with convexity 1 vs convexity 10.
> With convexity 100 it's still hard to identify a difference.  Maybe a very
> slight degradation?  With convexity 1000 the model rotates jerkily and it is
> hard to control.
>
> I increased complexity by making a 10x10 array of beveled cylinders, so 100
> objects.  In this case a difference is very clear.  With convexity 1 it
> rotates very responsively (with incorrect display).  With 2 it is also
> responsive.  With 10 there is a very noticeable lag with jerky
> rotation---it's hard to rotate the model.  With 100 it's unusable.
>
> Note that the time to produce the preview is the same regardless of the
> convexity value.
>

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Re: Bevelling a cylinder creates a void

nophead
Presumably it has to draw more pixels.

On Sat, 16 Jan 2021 at 18:59, jon <[hidden email]> wrote:
Excellent experiment!   Thank you!

I wonder why it gets jerky if the preview time is always the same

On 1/16/2021 1:55 PM, adrianv wrote:
> I did a little experimentation using the beveled cylinder as a test case.  It
> appears to display correctly with convexity 2 but wrong with convexity 1.  I
> don't notice any difference in performance with convexity 1 vs convexity 10.
> With convexity 100 it's still hard to identify a difference.  Maybe a very
> slight degradation?  With convexity 1000 the model rotates jerkily and it is
> hard to control.
>
> I increased complexity by making a 10x10 array of beveled cylinders, so 100
> objects.  In this case a difference is very clear.  With convexity 1 it
> rotates very responsively (with incorrect display).  With 2 it is also
> responsive.  With 10 there is a very noticeable lag with jerky
> rotation---it's hard to rotate the model.  With 100 it's unusable.
>
> Note that the time to produce the preview is the same regardless of the
> convexity value.
>

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Re: Bevelling a cylinder creates a void

adrianv
Why would higher convexity cause it to draw more pixels?  Where would these
extra pixels come from?


nophead wrote
> Presumably it has to draw more pixels.
>
> On Sat, 16 Jan 2021 at 18:59, jon &lt;

> jon@

> &gt; wrote:
>
>> Excellent experiment!   Thank you!
>>
>> I wonder why it gets jerky if the preview time is always the same
>>
>> On 1/16/2021 1:55 PM, adrianv wrote:
>> > I did a little experimentation using the beveled cylinder as a test
>> case.  It
>> > appears to display correctly with convexity 2 but wrong with convexity
>> 1.  I
>> > don't notice any difference in performance with convexity 1 vs
>> convexity
>> 10.
>> > With convexity 100 it's still hard to identify a difference.  Maybe a
>> very
>> > slight degradation?  With convexity 1000 the model rotates jerkily and
>> it is
>> > hard to control.
>> >
>> > I increased complexity by making a 10x10 array of beveled cylinders, so
>> 100
>> > objects.  In this case a difference is very clear.  With convexity 1 it
>> > rotates very responsively (with incorrect display).  With 2 it is also
>> > responsive.  With 10 there is a very noticeable lag with jerky
>> > rotation---it's hard to rotate the model.  With 100 it's unusable.
>> >
>> > Note that the time to produce the preview is the same regardless of the
>> > convexity value.
>> >
>>
>> _______________________________________________
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>>

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>>
>
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Re: Bevelling a cylinder creates a void

nophead
No idea but with a lower convexity some bits are missing, so I assume filling them in involves more drawing and that is why it is slower.

On Sat, 16 Jan 2021 at 20:25, adrianv <[hidden email]> wrote:
Why would higher convexity cause it to draw more pixels?  Where would these
extra pixels come from?


nophead wrote
> Presumably it has to draw more pixels.
>
> On Sat, 16 Jan 2021 at 18:59, jon &lt;

> jon@

> &gt; wrote:
>
>> Excellent experiment!   Thank you!
>>
>> I wonder why it gets jerky if the preview time is always the same
>>
>> On 1/16/2021 1:55 PM, adrianv wrote:
>> > I did a little experimentation using the beveled cylinder as a test
>> case.  It
>> > appears to display correctly with convexity 2 but wrong with convexity
>> 1.  I
>> > don't notice any difference in performance with convexity 1 vs
>> convexity
>> 10.
>> > With convexity 100 it's still hard to identify a difference.  Maybe a
>> very
>> > slight degradation?  With convexity 1000 the model rotates jerkily and
>> it is
>> > hard to control.
>> >
>> > I increased complexity by making a 10x10 array of beveled cylinders, so
>> 100
>> > objects.  In this case a difference is very clear.  With convexity 1 it
>> > rotates very responsively (with incorrect display).  With 2 it is also
>> > responsive.  With 10 there is a very noticeable lag with jerky
>> > rotation---it's hard to rotate the model.  With 100 it's unusable.
>> >
>> > Note that the time to produce the preview is the same regardless of the
>> > convexity value.
>> >
>>
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Re: Bevelling a cylinder creates a void

adrianv
With lower convexity some bits are missing...but the missing bits aren't
"pixels" they are larger regions.  I don't think any conclusion can be drawn
about how many pixels are drawn.  It seems more like differing computations
are done to determine what to draw, and with lower convexity the result is
that the wrong stuff is drawn.  


nophead wrote
> No idea but with a lower convexity some bits are missing, so I assume
> filling them in involves more drawing and that is why it is slower.
>
> On Sat, 16 Jan 2021 at 20:25, adrianv &lt;

> avm4@

> &gt; wrote:
>
>> Why would higher convexity cause it to draw more pixels?  Where would
>> these
>> extra pixels come from?
>>
>>
>> nophead wrote
>> > Presumably it has to draw more pixels.
>> >
>> > On Sat, 16 Jan 2021 at 18:59, jon &lt;
>>
>> > jon@
>>
>> > &gt; wrote:
>> >
>> >> Excellent experiment!   Thank you!
>> >>
>> >> I wonder why it gets jerky if the preview time is always the same
>> >>
>> >> On 1/16/2021 1:55 PM, adrianv wrote:
>> >> > I did a little experimentation using the beveled cylinder as a test
>> >> case.  It
>> >> > appears to display correctly with convexity 2 but wrong with
>> convexity
>> >> 1.  I
>> >> > don't notice any difference in performance with convexity 1 vs
>> >> convexity
>> >> 10.
>> >> > With convexity 100 it's still hard to identify a difference.  Maybe
>> a
>> >> very
>> >> > slight degradation?  With convexity 1000 the model rotates jerkily
>> and
>> >> it is
>> >> > hard to control.
>> >> >
>> >> > I increased complexity by making a 10x10 array of beveled cylinders,
>> so
>> >> 100
>> >> > objects.  In this case a difference is very clear.  With convexity 1
>> it
>> >> > rotates very responsively (with incorrect display).  With 2 it is
>> also
>> >> > responsive.  With 10 there is a very noticeable lag with jerky
>> >> > rotation---it's hard to rotate the model.  With 100 it's unusable.
>> >> >
>> >> > Note that the time to produce the preview is the same regardless of
>> the
>> >> > convexity value.
>> >> >
>> >>
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Re: Bevelling a cylinder creates a void

lleblanc
Hi,

Thanks to all for the many answers.

I'm with version 2019.05 and quite new to OpenSCAD, but as a (retired, if
one ever retires from that) programmer, I enjoy the code-like approach of
this design tool.

I didn't know about the F5/F6 commands, I always use the Render button, that
corresponds to F6.

My friend printed my STL and notes a small imperfection at the base of the
bevel (photo) - perhaps starting the cube  left of the cylinder would help,
as was suggested. It was easier to start right at the cylinder edge since I
readily know what the intercept height should be without further
computation.

Mirrycle.jpg <http://forum.openscad.org/file/t3095/Mirrycle.jpg>  



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Re: Bevelling a cylinder creates a void

adrianv
Looks to me like the slicer that converted the STL into gcode for the 3d
printer did something weird with the sharp corner at the bottom edge of the
hole.  That "missing" part is not missing in the OpenSCAD model.  
Presumably the solution to this is to round off the edge of the hole, which
is kind of tricky to do.  


lleblanc wrote

> Hi,
>
> Thanks to all for the many answers.
>
> I'm with version 2019.05 and quite new to OpenSCAD, but as a (retired, if
> one ever retires from that) programmer, I enjoy the code-like approach of
> this design tool.
>
> I didn't know about the F5/F6 commands, I always use the Render button,
> that
> corresponds to F6.
>
> My friend printed my STL and notes a small imperfection at the base of the
> bevel (photo) - perhaps starting the cube  left of the cylinder would
> help,
> as was suggested. It was easier to start right at the cylinder edge since
> I
> readily know what the intercept height should be without further
> computation.
>
> Mirrycle.jpg &lt;http://forum.openscad.org/file/t3095/Mirrycle.jpg&gt; 
>
>
>
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