poly_cylinder() now has a twist parameter.

readme.md

@@ -6116,6 +6116,16 @@ it gets the linear dimensions right. See <https://hydraraptor.blogspot.com/2011/
 
 The module provides `poly_circle()`, `poly_cylinder()` and `poly_ring()` that is useful for making printed washers and pillars.
 
+`poly_cylinder()` has a `twist` parameter which can be set to make the polygon rotate each layer.
+This can be used to mitigate the number of sides being small and make small holes stronger and more round, but is quite slow due to the
+large increase in the number of facets.
+When set to 1 the polygons alternate each layer, when set higher the rotation takes `twist + 1` layers to repeat.
+A small additional rotation is added to make the polygon rotate one more side over the length of the hole to make it appear round when
+veiwed end on.
+
+When `twist` is set the resulting cylinder is extended by `eps` at each end so that the exact length of the hole can be used without
+leaving a scar on either surface.
+
 
 [utils/core/polyholes.scad](utils/core/polyholes.scad) Implementation.
 
@@ -6133,7 +6143,7 @@ The module provides `poly_circle()`, `poly_cylinder()` and `poly_ring()` that is
 |:--- |:--- |
 | ```drill(r, h = 100, center = true)``` | Make a cylinder for drilling holes suitable for CNC routing, set h = 0 for circle |
 | ```poly_circle(r, sides = 0)``` | Make a circle adjusted to print the correct size |
-| ```poly_cylinder(r, h, center = false, sides = 0, chamfer = false)``` | Make a cylinder adjusted to print the correct size |
+| ```poly_cylinder(r, h, center = false, sides = 0, chamfer = false, twist = 0)``` | Make a cylinder adjusted to print the correct size |
 | ```poly_drill(r, h = 100, center = true)``` | Make a cylinder for drilling holes suitable for CNC routing if cnc_bit_r is non zero, otherwise a poly_cylinder. |
 | ```poly_ring(or, ir, sides = 0)``` | Make a 2D ring adjusted to have the correct internal radius |
 | ```poly_tube(or, ir, h, center = false)``` | Make a tube adjusted to have the correct internal radius |
@@ -6167,6 +6177,11 @@ The module provides `poly_circle()`, `poly_cylinder()` and `poly_ring()` that is
 |   1 | ```rod(9.5, 43)``` |  Smooth rod 9.5mm x 43mm |
 |   1 | ```rod(9, 41)``` |  Smooth rod 9mm x 41mm |
 
+### Printed
+| Qty | Filename |
+| ---:|:--- |
+|   1 | polyhole.stl |
+
 
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tests/polyholes.scad

@@ -21,7 +21,6 @@ include <../utils/core/core.scad>
 use <../vitamins/rod.scad>
 include <../vitamins/sheets.scad>
 
-module polyholes() {
 module positions()
     for(i = [1 : 10]) {
         translate([(i * i + i) / 2 + 3 * i , 8])
@@ -34,17 +33,48 @@ module polyholes() {
                     children();
     }
 
-    stl_colour(pp1_colour) linear_extrude(3, center = true)
+module polyhole_stl() {
+    stl("polyhole");
+
+    linear_extrude(3, center = true)
         difference() {
             square([100, 27]);
 
             positions()
                 poly_circle(r = $r);
         }
+}
+
+module alt_polyhole_stl() {
+    holes = [2.5, 2, 1.5];
+    n = len(holes);
+    size = [n * 10, 10, 10];
+    difference() {
+        translate([-size.x / n / 2, $preview ? 0 : -size.y / 2])
+            cube($preview ? [size.x, size.y / 2, size.z] : size);
+
+        for(i = [0 : n - 1])
+            translate([i * 10, 0])
+                if(i % 2)
+                    translate_z(size.z)
+                        poly_cylinder(r = holes[i] / 2, h = 2 * size.z, center = true, twist = i + 1);
+                else
+                    poly_cylinder(r = holes[i] / 2, h = size.z, center = false, twist = i + 1);
+    }
+}
+
+module polyholes() {
+    stl_colour(pp1_colour)
+        polyhole_stl();
 
     positions()
         rod(d = 2 * $r, l = 8 * $r + 5);
     //
+    // Alternating polyholes
+    //
+    translate([30, -40])
+        alt_polyhole_stl();
+    //
     // Poly rings
     //
     ir = 3 / 2;
@@ -74,4 +104,11 @@ module polyholes() {
             }
 }
 
+if($preview)
     polyholes();
+else {
+    polyhole_stl();
+
+    translate([50, -20])
+        alt_polyhole_stl();
+}

utils/core/polyholes.scad

@@ -22,6 +22,16 @@
 //! it gets the linear dimensions right. See <https://hydraraptor.blogspot.com/2011/02/polyholes.html>
 //!
 //! The module provides `poly_circle()`, `poly_cylinder()` and `poly_ring()` that is useful for making printed washers and pillars.
+//!
+//! `poly_cylinder()` has a `twist` parameter which can be set to make the polygon rotate each layer.
+//! This can be used to mitigate the number of sides being small and make small holes stronger and more round, but is quite slow due to the
+//! large increase in the number of facets.
+//! When set to 1 the polygons alternate each layer, when set higher the rotation takes `twist + 1` layers to repeat.
+//! A small additional rotation is added to make the polygon rotate one more side over the length of the hole to make it appear round when
+//! veiwed end on.
+//!
+//! When `twist` is set the resulting cylinder is extended by `eps` at each end so that the exact length of the hole can be used without
+//! leaving a scar on either surface.
 //
 function sides(r) = max(round(4 * r), 3);                                       //! Optimium number of sides for specified radius
 function corrected_radius(r, n = 0)   = r / cos(180 / (n ? n : sides(r)));      //! Adjusted radius to make flats lie on the circle
@@ -32,7 +42,24 @@ module poly_circle(r, sides = 0) { //! Make a circle adjusted to print the corre
     circle(r = corrected_radius(r,n), $fn = n);
 }
 
-module poly_cylinder(r, h, center = false, sides = 0, chamfer = false) {//! Make a cylinder adjusted to print the correct size
+module poly_cylinder(r, h, center = false, sides = 0, chamfer = false, twist = 0) {//! Make a cylinder adjusted to print the correct size
+    if(twist) {
+        slices = ceil(h / layer_height);
+        twist = min(twist, slices - 1);
+        sides = sides ? sides : sides(r);
+        rot = 360 / sides / (twist + 1) * (1 + 1 / slices);
+        if(center)
+            for(side = [0, 1])
+                mirror([0, 0, side])
+                    poly_cylinder(r = r, h = h / 2, sides = sides, twist = twist);
+        else
+            render(convexity = 5)
+                for(i = [0 : slices - 1])
+                    translate_z(i * layer_height - eps)
+                        rotate(rot * i)
+                            poly_cylinder(r = r, h = layer_height + 2 * eps, sides = sides);
+    }
+    else
         extrude_if(h, center)
             poly_circle(r, sides);