[OpenSCAD] Round shapes created in openscad are not smooth but hexigonal

Discussion:

FourthDr

2018-08-31 04:49:50 UTC

I was trying to make a coin for a friend to 3D print with a bossing on top. I
noticed that the coin or solid cylinder has a rough hexagonal shape to it.
How do I get a smooth round texture instead of the hex looking couture? I
also notice that round 3D models I modify in tinkercad then export to STL
also have a hexagonal surface after being exported, when they there
originally round without any noticeable hexigonalness. What's going on here?
How do I fix this problem? Could someone maybe provide some simple example
code?

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nop head

2018-08-31 07:43:53 UTC

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STL files only contain triangular facets so you can't have a true arc, only
a faceted approximation.

Similarly OpenSCAD represents all shapes with a boundary mesh made of
polygonal facets.

You can have as many facets as you want by setting $fn, you are not limited
to octogons. Higher values of $fn will slow down OpenSCAD.

You can also specify the minimum angle $fa and the minimum edge length with
$fs. This allows the number of edges to be set adaptively according to how
big the circle is.

For 3D printing I set $fa to 6 and $fa to half the extrusion width. That
gives 60 sides for large circles (best to make it a multiple of four).
Smaller circles hit the $fa limit and have less sides.

Post by FourthDr
I was trying to make a coin for a friend to 3D print with a bossing on top. I
noticed that the coin or solid cylinder has a rough hexagonal shape to it.
How do I get a smooth round texture instead of the hex looking couture? I
also notice that round 3D models I modify in tinkercad then export to STL
also have a hexagonal surface after being exported, when they there
originally round without any noticeable hexigonalness. What's going on here?
How do I fix this problem? Could someone maybe provide some simple example
code?
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Mark Peeters

2018-08-31 08:03:06 UTC

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nop head did you mean? " For 3D printing I set $fa to 6 and $fs to half the
extrusion width. That gives 60 sides for large circles (best to make it a
multiple of four). Smaller circles hit the $fs limit and have less sides"

Post by nop head
STL files only contain triangular facets so you can't have a true arc,
only a faceted approximation.
Similarly OpenSCAD represents all shapes with a boundary mesh made of
polygonal facets.
You can have as many facets as you want by setting $fn, you are not
limited to octogons. Higher values of $fn will slow down OpenSCAD.
You can also specify the minimum angle $fa and the minimum edge length
with $fs. This allows the number of edges to be set adaptively according to
how big the circle is.
For 3D printing I set $fa to 6 and $fa to half the extrusion width. That
gives 60 sides for large circles (best to make it a multiple of four).
Smaller circles hit the $fa limit and have less sides.

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nop head

2018-08-31 08:06:31 UTC

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Yes, sorry, typos that I thought I had already corrected before pressing
send.

Post by Mark Peeters
nop head did you mean? " For 3D printing I set $fa to 6 and $fs to half
the extrusion width. That gives 60 sides for large circles (best to make it
a multiple of four). Smaller circles hit the $fs limit and have less sides"

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FourthDr

2018-09-01 08:04:24 UTC

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Thanks Nophead for the reply. In a related question, since I am making a
model from scratch I need to know what units of measure are being used. I
see a scale in increments of 10. But is that inches or mm? Or something
else? I need to know how big the object is going to be and that it is the
correct size.

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a***@arnholm.org

2018-09-01 08:21:32 UTC

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Post by FourthDr
Thanks Nophead for the reply. In a related question, since I am making a
model from scratch I need to know what units of measure are being used. I
see a scale in increments of 10. But is that inches or mm? Or something
else? I need to know how big the object is going to be and that it is the
correct size.

The models are unit-less. However, in 3d printing a common convention is
to use mm. If you prefer to work in other units, you can scale the final
result to mm easily.

Carsten Arnholm

FourthDr

2018-09-01 08:30:59 UTC

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Export to STL seems to be in mm. But I didn't set any units.

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nop head

2018-09-01 09:00:33 UTC

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STL is unit-less also. It is the slicer in a 3D printing chain that decides
1 unit is 1mm.

Post by FourthDr
Export to STL seems to be in mm. But I didn't set any units.
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Rob Ward

2018-09-01 09:33:31 UTC

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.STL in mm is just a very happy coincidence, or someone's very good anticipation for an important technology. Thanks folks!!
Cheers, RobW

Post by nop head
STL is unit-less also. It is the slicer in a 3D printing chain that decides
1 unit is 1mm.