Added screw_polysink().

readme.md

@@ -2933,6 +2933,7 @@ Machine screws and wood screws with various head styles.
 | ```screw_head_depth(type, d = 0)``` | How far a counter sink head will go into a straight hole diameter d |
 | ```screw_longer_than(x)``` | Returns shortest screw length longer or equal to x |
 | ```screw_nut_radius(type)``` | Radius of matching nut |
+| ```screw_polysink_r(type, z)``` | Countersink hole profile corrected for rounded staircase extrusions. |
 | ```screw_shorter_than(x)``` | Returns longest screw length shorter than or equal to x |
 
 ### Modules
@@ -2941,6 +2942,7 @@ Machine screws and wood screws with various head styles.
 | ```screw(type, length, hob_point = 0, nylon = false)``` | Draw specified screw, optionally hobbed or nylon |
 | ```screw_and_washer(type, length, star = false, penny = false)``` | Screw with a washer which can be standard or penny and an optional star washer on top |
 | ```screw_countersink(type, drilled = true)``` | Countersink shape |
+| ```screw_polysink(type)``` | A countersink hole made from stacked polyholes for printed parts |
 
 ![screws](tests/png/screws.png)
 

vitamins/screw.scad

@@ -258,7 +258,7 @@ module screw_countersink(type, drilled = true) { //! Countersink shape
     if(head_type == hs_cs || head_type == hs_cs_cap)
         translate_z(-head_height)
             if(drilled)
-                cylinder(h = head_height, r1 = 0, r2 = head_rad + head_t);
+                cylinder(h = head_height + eps, r1 = 0, r2 = head_rad + head_t);
             else
                 intersection() {
                     cylinder(h = head_height + eps, r1 = 0, r2 = head_rad + head_t);
@@ -267,6 +267,24 @@ module screw_countersink(type, drilled = true) { //! Countersink shape
                 }
 }
 
+function screw_polysink_r(type, z) = //! Countersink hole profile corrected for rounded staircase extrusions.
+    let(rad = screw_radius(type),
+        head_t = rad / 5,
+        head_rad = screw_head_radius(type)
+    )
+    limit(head_rad + head_t - z + (sqrt(2) - 1) * layer_height / 2, screw_clearance_radius(type), head_rad);
+
+module screw_polysink(type) { //! A countersink hole made from stacked polyholes for printed parts
+    head_depth = screw_head_depth(type);
+    assert(head_depth, "Not a countersunk screw");
+    layers = ceil(head_depth / layer_height);
+    for(i = [0 : layers - 1], side = [-1, 1])
+        translate_z(side * (i + 0.5) * layer_height)
+            poly_cylinder(r = screw_polysink_r(type, i * layer_height + layer_height / 2), h = layer_height + 2 * eps, center = true);
+
+    poly_cylinder(r = screw_clearance_radius(type), h = 100, center = true);
+}
+
 module screw_and_washer(type, length, star = false, penny = false) { //! Screw with a washer which can be standard or penny and an optional star washer on top
     washer = screw_washer(type);
     head_type = screw_head_type(type);