basic questions $fn

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basic questions $fn

claudio
hi,

i am new into 3d and want to use this tool to make some 3d prints.
first modelling in openscad and then slicing and printing on prusa i3
mk3.

my question about modelling, i havt this simple code:

$fn = 10;
difference() {
        cube (size = [40,30,4]);
        # translate ([20,10,0]) {
         cylinder(d = 7, h = 4);
     }
}

now when i render the model the hole does not look round. wehn i alter
the parameter $fn to 100 it looks round. is this parameter $fn just a
visual thing or does my 3d print (after slicing) come out as it looks on
the screen with edges?

and next question: i want to have this plate with a hole. translate
starts from 0 and the hole/cylinder is exact 4 high, as the plate. is
that ok? or do i have to set translet -1 and cylinder high 6, as shown
on the manual and sample?

thank you, claudio

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Re: basic questions $fn

nophead
Yes the STL file will be same as shown on the screen. It only contains triangles so you can't have a round circle.

For 3D FFF printing I use $fa = 6 and $fs = half my filament width to get good curves without ridiculously small segments.

You should avoid coincident surfaces by subtracting a longer cylinder when drilling holes. To avoid the extra translate I often use a cylinder twice as long plus 1 and center = true when drilling.

On 12 October 2017 at 15:38, <[hidden email]> wrote:
hi,

i am new into 3d and want to use this tool to make some 3d prints.
first modelling in openscad and then slicing and printing on prusa i3 mk3.

my question about modelling, i havt this simple code:

$fn = 10;
difference() {
        cube (size = [40,30,4]);
        # translate ([20,10,0]) {
        cylinder(d = 7, h = 4);
    }
}

now when i render the model the hole does not look round. wehn i alter the parameter $fn to 100 it looks round. is this parameter $fn just a visual thing or does my 3d print (after slicing) come out as it looks on the screen with edges?

and next question: i want to have this plate with a hole. translate starts from 0 and the hole/cylinder is exact 4 high, as the plate. is that ok? or do i have to set translet -1 and cylinder high 6, as shown on the manual and sample?

thank you, claudio

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Re: basic questions $fn

atnbueno
In reply to this post by claudio
Hello, Claudio.

You will see much more detail in your screen than in your print. For 3D printing you don't need $fn values as high as the ones needed to show a smooth curve surface in your monitor. I usually prefer to indicate the minimum size of a face ($fs) than the number of faces ($fn). See here: https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Other_Language_Features#.24fa.2C_.24fs_and_.24fn

If I understand your second question, yes, you have to add a bit of extra height to the cylinder that does the hole. I personally like adding tiny extras so I know any .00x-ended value is avoiding coincident faces. An example of both things:

$fs=0.4;
difference() {
cube([20, 20, 4], true);
translate(-0.001) cylinder(r=4, h=4.002, center=true);
}


2017-10-12 16:38 GMT+02:00 <[hidden email]>:
hi,

i am new into 3d and want to use this tool to make some 3d prints.
first modelling in openscad and then slicing and printing on prusa i3 mk3.

my question about modelling, i havt this simple code:

$fn = 10;
difference() {
        cube (size = [40,30,4]);
        # translate ([20,10,0]) {
        cylinder(d = 7, h = 4);
    }
}

now when i render the model the hole does not look round. wehn i alter the parameter $fn to 100 it looks round. is this parameter $fn just a visual thing or does my 3d print (after slicing) come out as it looks on the screen with edges?

and next question: i want to have this plate with a hole. translate starts from 0 and the hole/cylinder is exact 4 high, as the plate. is that ok? or do i have to set translet -1 and cylinder high 6, as shown on the manual and sample?

thank you, claudio

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-- 
Regards from Spain,
Antonio

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Re: basic questions $fn

claudio
In reply to this post by nophead
thank you for the first answer.....
i just dont understand exactely your second idea below...
mybe with a small sample script?

> You should avoid coincident surfaces by subtracting a longer cylinder
> when drilling holes. To avoid the extra translate I often use a
> cylinder twice as long plus 1 and center = true when drilling.

my sample:
>> $fn = 10;
>> difference() {
>> cube (size = [40,30,4]);
>> # translate ([20,10,0]) {
>> cylinder(d = 7, h = 4);

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Re: basic questions $fn

nophead
This is what I do:

$fn = 10;
height = 4;
difference() {
    cube (size = [40,30,height]);
    #translate ([20,10,0])
        cylinder(d = 7, h = 2 * height + 1, center = true);
}


Or if I am lazy I just use h = 100;



On 12 October 2017 at 16:02, <[hidden email]> wrote:
thank you for the first answer.....
i just dont understand exactely your second idea below...
mybe with a small sample script?

You should avoid coincident surfaces by subtracting a longer cylinder
when drilling holes. To avoid the extra translate I often use a
cylinder twice as long plus 1 and center = true when drilling.

my sample:
$fn = 10;
difference() {
cube (size = [40,30,4]);
# translate ([20,10,0]) {
cylinder(d = 7, h = 4);

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Re: basic questions $fn

claudio
hi all....

thank you all for your answers... i think i got that :)
now i am playing and modifying my code....
next question will come ;-)

take care, claudio



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Sent from: http://forum.openscad.org/

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