Thanks for the replies and sorry if this starts a second thread - I seem to
be blocked from replying on the web.

I am using 2015.03-2 on Windows which seems rather old but according to the
web site it's the latest version.

Your image looks plenty smooth - basically when I get these things 3d
printed the 'tree rings' are visible and I'd rather they were not.

I don't get a smoother result at $fn=1000. 570 is about as good as it gets
and has about 16 concentric rings.

I can't really use $fn on the proper model because there are also small
radius curves and having so many facets on a small curve will push up the
model complexity too much.

The attached image has the contrast pushed up to hopefully show what I get.

Is there a later version? Are the dev snapshots suitable for everyday use
for example?

Regards, Andy

Thanks. I tried out the snapshot build.

The good news is that it makes a lovely job of my simple example with $fa set to 0.3… which is equivalent to $fn=1200

The not so good news is that the tree rings remain just as bad when doing a rotate_extrude of the DXF with the same setting, same cylinder and dome diameter.

I will need to experiment some more another day. If all else fails I may need to drop the DXF and draw the end using code.

Regards Andy

From: nophead [via OpenSCAD] [mailto:ml+s1091067n25195h23@n5.nabble.com]
Sent: 10 January 2019 20:08
To: andy_at_blighty <andycarlson@acm.org mailto:andycarlson@acm.org >
Subject: Re: Cant smooth this domed end

Yes I have been using snapshots for years with few problems.

What type of entities (Lines, Arcs, Polylines) are in your DXF file?
Not sure if this is your problem, but if you have Polylines (joined Line and
ARC segments) in the DXF file Openscad seems to interpret the Arc segments
as straight line segments.  You may need to explode the Polylines before
creating the DXF file.

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They are arcs. The domed end is an arc and then there are small radius
fillets between that and the sides of the cylinder.

I've now done some more on this. I lifted all of the coordinates from CAD
and redid the whole shape using OpenSCAD primitives.

The good news is that it then became super-smooth in my test.

The not so good news is that I then pasted the exact same code into my real
model, removed the DXF extrude. and the tree-rings were still there. The
render time also went up from about 2 minutes to 30.

So I'm stuck now. I can't really offer my entire model as a test case (and
it would be a pretty unusable test case if I did). At the moment I think my
best option is to set $fa to 0.65 (the lowest value that improves the
tree-rings) and go for a 3d print with that.

Regards, Andy

From: cbernhardt [via OpenSCAD] [mailto:ml+s1091067n25206h64@n5.nabble.com]
Sent: 11 January 2019 13:44
To: andy_at_blighty andycarlson@acm.org
Subject: Re: Cant smooth this domed end

What type of entities (Lines, Arcs, Polylines) are in your DXF file?
Not sure if this is your problem, but if you have Polylines (joined Line and

ARC segments) in the DXF file Openscad seems to interpret the Arc segments
as straight line segments.  You may need to explode the Polylines before
creating the DXF file.

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Note also that if this dome is at the top of the print, your ability to
avoid tree rings is dependent on the Z resolution of your printer.

Yes there are all sorts of questions about printer resolution and artefacts.
I've actually had this done on two different printer technologies and with
different orientations.

My main concern with the model is to make sure it is not contributing to any
artefacts.

Regards, Andy

From: JordanBrown [via OpenSCAD] [mailto:ml+s1091067n25212h50@n5.nabble.com]

Sent: 11 January 2019 18:05
To: andy_at_blighty andycarlson@acm.org
Subject: Re: Cant smooth this domed end

Note also that if this dome is at the top of the print, your ability to
avoid tree rings is dependent on the Z resolution of your printer.

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Could you post a link to your code that uses rotate_extrude of the DXF file
and also a link to your DXF file?

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Not sure if I can attach a DXF but will have a try...

The code is very simple. It has a general setting for $fs and $fa (as per my
real model which uses these values for other parts) . Then $fa is overridden
for the domed end DXF

$fs=.05;
$fa=2;

profdxf = "end-dome.dxf";

rotate_extrude(convexity=10) {
import(profdxf,$fa=.3);
}

If I mess with the $fa value on the DXF import then the tree rings get more
in number and smaller down to about $fa=0.65 but as I go lower they don't
continue this behaviour. At 0.3 for example I see irregular sizes of ring -
for example the first complete ring outside the centre is a good deal
narrower than the second. I've attached an image - again with the contrast
increased.

Regards Andy

-----Original Message-----
From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of
cbernhardt
Sent: 11 January 2019 19:53
To: discuss@lists.openscad.org
Subject: Re: [OpenSCAD] Cant smooth this domed end

Could you post a link to your code that uses rotate_extrude of the DXF file
and also a link to your DXF file?

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I tried your model using your DXF file with many different values of $fn,
$fa, and $fs and it seems that OpenSCAD does apply these variables to arcs
in DXF files the same way as it applies them to objects created by OpenSCAD.
I took your DXF file and did a linear_extrude using various values of $fn.
The picture below shows the STL files of the results.  Looks like 360 is the
upper limit for $fn when inserting a DXF file.  I also tried various values
of $fs and $fa with similar results.
http://forum.openscad.org/file/t1309/arcs.jpg

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