make spin with slices using fast layer height

diff --git a/spin-data.scad b/spin-data.scad
index 0c83d85bcad1a929d25e26a26e08fcd362b2cd9e..4d4fd0dec60f9b947024b8c9a82fec96f9878f67 100644 (file)
--- a/spin-data.scad
+++ b/spin-data.scad
@@ -4,7 +4,7 @@
 /* spin thing that erin likes */
 $fn = 50;
 
-layer_height = 0.15;
+layer_height = 0.35;
 
 weight = "penny";
 // weight = "608zz";
@@ -69,35 +69,55 @@ module cap(bearing_inner_radius,
 module fillet(r) {
   offset(r = -r) { offset(delta = r) { children(); } } }
 
-module spin_footprint(weight_radius,
-                      bearing_radius,
-                      round_extra,
-                      wall,
-                      arms) {
-  thinner_radius = (bearing_radius < weight_radius)?
-    bearing_radius : weight_radius;
-  fillet(thinner_radius / 2) {
-    for(arm = [0 : arms - 1]) {
-      hull() {
-        circle(bearing_radius + round_extra);
-        rotate( (arm / arms) * 360 ) {
-          translate([bearing_radius + wall + weight_radius, 0]) {
-            circle(weight_radius + round_extra); } } } } } }
-
 module mirrored(axis) {
   children();
   mirror(axis) children(); }
 
-module spin(weight_radius,
-            weight_thickness,
-            bearing_radius,
-            bearing_thickness,
-            weight_lip_overhang = 0.3,
-            bearing_lip_overhang = 0.3,
-            wall = 3,
-            arms = 3,
-            layer_height = 0.15) {
-  layer_height = 0.15;
+module spin_slice(weight_radius,
+                  bearing_radius,
+                  round_extra,
+                  wall,
+                  arms) {
+  joiner_radius = (bearing_radius + weight_radius) / 2;
+
+  bearing_xy = [0, 0];
+  // a = side along x axis
+  a = bearing_radius + weight_radius + wall;
+  // b = side from center to joiner
+  b = bearing_radius + joiner_radius + round_extra;
+  // c = side between joiner and arm center
+  c = joiner_radius + weight_radius + round_extra;
+
+  weight_xy = [a, 0];
+
+  cos_C = (pow(a, 2) + pow(b, 2) - pow(c, 2)) / (2 * a * b);
+  sin_C = sqrt(1 - pow(cos_C, 2));
+
+  joiner_xy = [cos_C, sin_C] * b;
+
+  for(arm = [0 : arms - 1]) {
+    rotate(arm * (360 / arms)) {
+      difference() {
+        union() {
+          translate(bearing_xy) {
+            circle(bearing_radius + round_extra); }
+          translate(weight_xy) {
+            circle(weight_radius + round_extra); }
+          mirrored([0, 1]) {
+            polygon([bearing_xy, weight_xy, joiner_xy]); } }
+        mirrored([0, 1]) {
+          translate(joiner_xy) {
+            circle(joiner_radius); } } } } } }
+
+module spin_slices(weight_radius,
+                   weight_thickness,
+                   bearing_radius,
+                   bearing_thickness,
+                   weight_lip_overhang = 0.3,
+                   bearing_lip_overhang = 0.3,
+                   wall = 3,
+                   arms = 3,
+                   layer_height = 0.15) {
   thicker_thickness = (bearing_thickness > weight_thickness) ?
     bearing_thickness : weight_thickness;
   calculated_height = thicker_thickness + 2 * wall;
@@ -105,10 +125,18 @@ module spin(weight_radius,
   actual_height = layers * layer_height;
   round_radius = actual_height / 2;
 
+  /* rounding the outside edge of the spinner with a semi-circle leads
+     to a shape that an overhang on the second layer several times the
+     thickness of a printed extrusion width.
+
+     rather than using a full semi-circle, this code aims to use just the
+     portion in the middle, where the overhang is less severe */
   old_start = 0;
   old_end = (layers / 2) - 1;
 
-  new_start = old_end / 16;
+  /* add one to have some thickness all around weight holes
+     for first layer */
+  new_start = old_end / 8 + 1;
   new_end = old_end;
 
   old_range = old_end - old_start;
@@ -116,24 +144,41 @@ module spin(weight_radius,
 
   factor = new_range / old_range;
 
-  initial_adjacent = round_radius - (new_start * layer_height);
+  /* initial adjacent is adjusted to (new start - 1) to allow some
+     thickness all around weight holes on first layer */
+  initial_adjacent = round_radius - ((new_start - 1) * layer_height);
   initial_angle = acos(initial_adjacent / round_radius);
   initial_round_extra = initial_adjacent * tan(initial_angle);
-  
-  mirrored([0, 0, 1]) {
-    for(layer = [0 : (layers / 2) - 1]) {
-      translate([0, 0, layer * layer_height - actual_height / 2]) {
-        linear_extrude(height = layer_height) {
-          new_layer = (layer - old_start) * factor + new_start;
-          adjacent = round_radius - (new_layer * layer_height);
-          angle = acos(adjacent / round_radius);
-          round_extra = adjacent * tan(angle) - initial_round_extra;
-          echo(round_extra);
-          spin_footprint(weight_radius,
-                         bearing_radius,
-                         round_extra,
-                         wall,
-                         arms); } } } } }
+
+  difference() {
+    mirrored([0, 0, 1]) {
+      for(layer = [0 : (layers / 2) - 1]) {
+        translate([0, 0, layer * layer_height - actual_height / 2]) {
+          linear_extrude(height = layer_height) {
+            new_layer = (layer - old_start) * factor + new_start;
+            adjacent = round_radius - (new_layer * layer_height);
+            angle = acos(adjacent / round_radius);
+            round_extra = adjacent * tan(angle) - initial_round_extra;
+            spin_slice(weight_radius,
+                       bearing_radius,
+                       round_extra,
+                       wall,
+                       arms); } } } }
+    cylinder(h = actual_height + 0.1,
+             r = bearing_radius - bearing_lip_overhang,
+             center = true);
+    cylinder(h = bearing_thickness + 0.1,
+             r = bearing_radius + 0.1,
+             center = true);
+    for(arm = [0 : arms - 1]) {
+      rotate(arm * (360 / arms)) {
+        translate([bearing_radius + wall + weight_radius, 0]) {
+          cylinder(h = actual_height + 0.1,
+                   r = weight_radius - weight_lip_overhang,
+                   center = true);
+          cylinder(h = weight_thickness + 0.1,
+                   r = weight_radius + 0.1,
+                   center = true); } } } } }
 
 /*
   This file is part of 3d-printables.

diff --git a/spin.scad b/spin.scad
index 3697f5edaddc815b732cb4d9be43ae51f5778e00..1d3bfb8efebd12a681605cf55eaa2d7a56bb512b 100644 (file)
--- a/spin.scad
+++ b/spin.scad
@@ -4,18 +4,18 @@
 /* spin thing that erin likes */
 include<spin-data.scad>
 
-object = "spin";
+object = "spin_slices";
 
-if (object == "spin") {
-  spin(weight_radius,
-       weight_thickness,
-       bearing_radius,
-       bearing_thickness,
-       weight_lip_overhang,
-       bearing_lip_overhang,
-       wall,
-       arms,
-       layer_height); }
+if (object == "spin_slices") {
+  spin_slices(weight_radius,
+              weight_thickness,
+              bearing_radius,
+              bearing_thickness,
+              weight_lip_overhang,
+              bearing_lip_overhang,
+              wall,
+              arms,
+              layer_height); }
 else if (object == "cap") {
   cap(bearing_inner_radius,
       bearing_cap_footprint_radius,