I have tried this, but it doesnot make a perfect circle.
Howto?

st="Thomas Leonard Gertz";
width=140 ;
thickness=2 ;
chars=len(st)+1 ;
degrees=180 ;
for (i = [1:chars]) {
translate([ iwidth/chars,sin(idegrees/chars)*width/2,0])
linear_extrude(thickness)
text(st[i-1]);
}
translate([width/2,0,0])
rotate_extrude(angle=degrees) translate([width/2,0])
square([thickness,thickness]);

Thomas Leonard Gertz
Kerteminde, Danmark

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

I donot know why but it works without cos or sin only PI.

Thomas Leonard Gertz
Kerteminde, Danmark

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

Something like this?
http://forum.openscad.org/file/t1309/text_on_circle.jpg

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

What you do is not a circle, it's half a sine wave.

Is it something like this you want to do?

st="Thomas Leonard Gertz";
width=140 ;
thickness=2 ;
chars=len(st)+1 ;
degrees=180 ;
for (i = [1:chars]) {
rotate([0,0,90-i*(180/chars)])
translate([0,width/2,0])
linear_extrude(thickness)
text(st[i-1],halign="center");
}

rotate_extrude(angle=degrees) translate([width/2,0])
square([thickness,thickness]);

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

I turned it into a more generic module for this (works best with fixed width
fonts):

module
circletext(mytext,textsize=20,myfont="Arial",radius=100,thickness=1,degrees=360,top=true){

chars=len(mytext)+1;

for (i = [1:chars]) { 
		rotate([0,0,(top?1:-1)*(degrees/2-i*(degrees/chars))])
		translate([0,(top?1:-1)*radius-(top?0:textsize/2),0]) 
		//linear_extrude(thickness) 
		text(mytext[i-1],halign="center",font=myfont,size=textsize); 
} 

}

circletext("My text goes here",textsize=20,degrees=160,top=true);

circletext("Text can be underneath as
well",textsize=15,degrees=180,top=false);

--
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For the specific case of a cylinder, the text can be rotated and extruded.
For sufficiently large strings of text, the effect is pretty good as is, but
each character is still a linear segment.  Intersecting with a
high-resolution cylinder gives a fairly smooth curve over the text as a
whole.

module
circletext(mytext,textsize=20,myfont="Arial",radius=100,thickness=1,degrees=360,top=true){

    chars=len(mytext)+1; 
    
    for (i = [1:chars]) { 
                   

rotate([0,0,(top?1:-1)(degrees/2-i(degrees/chars))])

translate([0,(top?1:-1)*radius-(top?0:textsize/2),0])
rotate ([90,0,0])
linear_extrude(thickness)
text(mytext[i-1],halign="center",font=myfont,size=textsize);
}
}

intersection() {
cylinder (r=120, h=300, $fn=1000);
circletext("Text can be underneath as
well",textsize=15,degrees=180,top=false, thickness=20);
}

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One minor improvement might be to use a technique I came up with to bend an
image into a cylinder: https://www.thingiverse.com/thing:322720

Instead of rotating each character separately, render the text into a flat
"stamp", then "emboss" that into a cylinder by rotating the cylinder and
advancing the plate a small amount each time. Intersecting with the cylinder
instead of differencing against it would produce a positive model.

This has the advantage that the error can be arbitrarily minimized, and you
get whatever kerning/character spacing benefits the text system provides
instead of having each character be spaced by an identical amount.

The downside is that it is computationally complex, and I don't think it is
possible to know the horizontal extent of the text string so that has to be
approximated somehow or adjusted until appropriate.

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