On my printer (an average FDM) any circle segment smaller than 1mm makes no
difference. It just makes the Gcode file bigger, which may result in stalls
(the controller cant parse the Gcode fast enough). I usually go for about
3mm features on large circles .... but then I am not making art-objects.

YMMV as they say

On Fri, 9 Jun 2023 at 10:53, Karl Exler karl.exler@meinklang.cc wrote:

It affects printing as well as viewing.
I use $fn=6; to create hexagonal wells in flat jigs I use to align
tokens for laser engraving. Here's a snippet from my code for 3d
printing the jig:

      translate(wCtr)
        rotate([0,0,30])
          cylinder(d=hD,h=wH,center=true,$fn=6);

-Bob

Karl Exler wrote on 6/9/2023 4:53 AM:

ah.. thanks!
Is there an recommendation for $fn for printing round elements?  I
understand that I can print a rectanngle by "circle(d=50, $fn=3). But
when I want to get a "real" circle.. I always use $fn=100... but perhaps
this is useless and too much and only costs ressources?

greetings
Karl

Am 09.06.23 um 11:36 schrieb Bob Kauffman Starkey:

Think about it:  if you make a 100-sided "circle" and print it to fill the
200mm build plate of a typical full-sized printer you'll have facets that
are 6mm (2 pi * 200 /100).  Do you think you can notice such facets on the
output?  If you think a 1mm facet is a good size in the output then you
can have a circumference of at most 100, which means a 15.9 mm diameter.
I would say that $fn=100 is sometimes unnecessarily large and sometimes too
small, depending on the diameter of your circle.

You can examine your output and see if facets are visible.  I have various
printed objects where I can clearly see and feel facets.  Using $fs and $fa
instead of $fn may be an easier way to ensure that the number of segments
is large enough.

On Fri, Jun 9, 2023 at 5:58 AM Karl Exler karl.exler@meinklang.cc wrote:

On 6/9/23 04:54, Karl Exler wrote:

Works for both.  Here's my $0.02:
Screws are better when bigger. For really big ones, hard maple in a
suitable milling machine. I'm making a vise screw for woodworkers, 50mm
in diameter, with a 6mm tooth in buttress thread style, 2 start 12mm
pitch which makes the half nuts identical. I am printing the half nuts
in petg because its far more resilient than PLA, and my half nuts are
around 12 engaged teeth. Any smaller screws IMO should be put in
suitably sized holes as self tapping. That also rules out PLA as its
strong enough but way too brittle.

One gotcha: The printer will lay plastic half the nozzle size beyond the
openscad size on both sides on each plastic to air wall, so holes to
pass a 5mm screw s/b not less than 5.6mm for a clearance pass, and down
around 5.2mm to 5.3mm for self threading.

Like I said, my $0.02. ymmv.  And is highly dependent on how well the
printer is calibrated.  The speed you drive it at is more important than
the brand name on the printer. My impression of the mini is that the
temps needed for petg will make short work of the printhead, I've only
found one printhead that is long term usable at PETG temps of 235-250C
and it needs an after market titanium heat break and hard copper hot
block. And if using any cf filled plastic, a carbide nozzle. Some corexy
printers can run much faster.

Cheers, Gene Heskett.

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.

• Louis D. Brandeis
  Genes Web page http://geneslinuxbox.net:6309/

$fa = 6;
$fs = extrusion_width / 2;

Works for me for 3D printing.

On Fri, 9 Jun 2023 at 12:57, gene heskett gheskett@shentel.net wrote:

On 6/9/2023 2:57 AM, Karl Exler wrote:

As others have hinted, but nobody really seems to have explained...
don't use $fn to control circles.  Yes, its behavior is obvious, but it
controls all circles, large and small, and no one value is right.

Use $fs and $fa.

$fa controls the minimum angle between facets, and effectively controls
larger circles.  I did a test print with a large arc (maybe 100mm
radius?) and 5° (a 72-gon) wasn't small enough; facets were clearly visible.

$fs controls the minimum size of a facet, and effectively controls small
circles.  Setting it to, say, 0.5, will mean that a circle with a 1mm
radius will be a 13-gon, which is probably fine for something that small.

Do some test prints and pick your own favorite values, but mostly once
you pick a pair of values that you like you should be able to use them
across the board.