If you don't care about your engraving wrapping around surface's curvature, only the depth being consistent, you can subtract a smaller version of the cylinder from the thing you're subtracting.
On Apr 14, 2021, 00:59 -0700, amundsen roald.baudoux@brutele.be, wrote:

https://www.thingiverse.com/thing:1668883

On Wed, 14 Apr 2021, 8:04 pm Whosawhatsis, whosawhatsis@gmail.com wrote:

On 14.04.2021 09:58, amundsen wrote:

I don't think there is a direct way to generally do that in OpenSCAD,
but you can combine OpenSCAD with other tools to do it.

Let us say you use OpenSCAD to model a cylinder and another OpenSCAD
session to model the text to be engraved:

cylinder.scad:

cylinder(r=30,h=30);

cylinder_text.scad

linear_extrude(5)
text("Text on a cylinder");

To engrave the text on the cylinder, you can do:

1 OpenSCAD: cylinder.scad => Save as 'cylinder.obj'

2 OpenSCAD: cylinder_text.scad => save as 'cylinder_text.obj'

3 Remesh the 'cylinder_text.obj' file to max 2mm size triangles.
To do this, use 'polyfix', a console application included with AngelCAD

$ polyfix -remesh=2.0 -dtol=0.001 -overwrite ./cylinder_text.obj -out=*.obj

The result is a new version of 'cylinder_text.obj' with denser triangle
mesh, to be used in step 4 below.

4 AngelCAD: cylinder_engrave.as => cylinder_engrave.stl
This script imports the 2 .obj files created with OpenSCAD, wraps the
'cylinder_text.obj' around a r=28mm cylinder and performs the engraving
by subtracting it from 'cylinder.obj'

Files and more details here, including final engraved cylinder
https://gist.github.com/arnholm/de12d1768cc552a416a6f9edebd0a81c

https://github.com/arnholm/angelcad/releases

Regards
Carsten Arnholm

I have code that does this, but it is VERY slow on any significant amounts
of text (The bend module is the key one, the rest of it sets up what to
bend):

module inscribe2d(depth, baseOffset, width = 0, height = 0) {
translate([0, 0, baseOffset - depth]) {
linear_extrude(depth, center = false) {
if (width > 0 || height > 0) {
resize([width, height], auto=[true, true, false]) {
children();
}
} else {
children();
}
}
}
}

module monogram(text, font, depth, baseOffset, width = 0, height = 0) {
inscribe2d(depth, baseOffset, width, height) {
if (is_undef(font)) {
text(text, size = 10, valign = "center", halign = "center");
} else {
text(text, font = font, size = 10, valign = "center", halign =
"center");
}
}
}

module bend(radius, angleOffset = 0) {
stepAngle = 360 / $fn;
stepWidth = 2 * PI * radius / $fn;
union() {
for (step = [-$fn : $fn]) {
angle = step * stepAngle + angleOffset;
offset = step * stepWidth;
translate([0, 0, radius]) {
rotate([0, -angle, 0]) {
translate([-offset, 0, -radius]) {
intersection() {
children();
translate([offset, 0, 0]) {
cube(size = [stepWidth, stepWidth * $fn, stepWidth * $fn],
center = true);
}
}
}
}
}
}
}
}

module labeledDisc(radius, thickness, label = undef) {
difference() {
rotate([0, 0, 180 / $fn]) {
cylinder(r = radius, h = thickness, center = true);
}
if (SHOW_TEXT && !is_undef(label)) {
rotate([90, 0, -90]) {
translate([0, 0, -radius]) {
bend(radius = radius, angleOffset = 90) {
scale([-1, 1, 1]) {
monogram(label, height = (thickness * 0.8), depth = 2.01,
baseOffset = 2);
}
}
}
}
rotate([90, 180, -90]) {
translate([0, 0, -radius]) {
bend(radius = radius, angleOffset = 90) {
scale([-1, 1, 1]) {
monogram(label, height = (thickness * 0.8), depth = 2.01,
baseOffset = 2);
}
}
}
}
}
}
}

On Wed, Apr 14, 2021 at 10:09 AM NateTG nate-openscadforum@pedantic.org
wrote:

This looks very good, but could you please provide a working example
call? It is not completely clear to me how to use your code.

Cheers,
Maurice

A better version of it would be in the attached bend.scad. I had at least
one bit of code leftover from the project I stole it from, and it depended
on $fn being set, which is not always the case... the render() call
wrapping the actual call to labeledDisc helps a lot for the speed, although
it is still not blazingly fast by any means.

On Wed, Apr 14, 2021 at 4:55 PM Maurice van Peursem openscad@vanpeursem.net
wrote:

I will note that I just noticed that the code doesn't work proper if $fn is
less than 8, I am still working out what I did wrong

On Wed, Apr 14, 2021 at 5:50 PM A. Craig West acraigwest@gmail.com wrote:

cacb wrote

Here's my attempt:

====

use <alphabet_points.scad>;
use <path_extrude.scad>;

myPath = [[58,0,0], [62,0,0]];

module extrudeLetter(pointSets, extrudeType, path){
for(ps = pointSets){
mapExtrude(extrudeType, ps, path, $fn=5);
}
}

rotate([0,0,-$t * 360]){
difference(){
cylinder(r=60, h=100, $fn=100, center=true);
for(ltl = [0, 1]){
lArr = ["ENGRAVED", "TEXT"][ltl];
sw = strLen(lettersToNumbers(lArr))2;
cCirc = 2 * PI * 60;
for(lp = [0:(len(lArr)-1)]){
rotate([0,0,lp16 -(sw/cCirc * 180)]) translate([0,0,-ltl*30]){
extrudeLetter(ltrPoints(lettersToNumbers(lArr[lp])[0])*2,
"radialCylinder", myPath);
}
}
}
}
}

====

This uses my point-based OpenSCAD font (only capital letters at the moment):

https://www.thingiverse.com/thing:4826453

And my guided path extrusion code (which I just adapted now to do a radial
extrude):

https://www.thingiverse.com/thing:4824085

This doesn't render properly in preview mode (presumably due to the issues
with assuming a curved surface, i.e. the end caps of the extrusion, is
flat), but seems to work okay in the fully-rendered mode.

http://forum.openscad.org/file/t452/text_engraved.png

--
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