Added SBR rails

This change adds
- SBR rails. For now only SBR16
- The bearing block that goes with it (SBR16UU)
- An 'open' linear bearing (LM16UUOP) that is used by the bearing block
- A 28mm circlip that has a wider opening than then normal circlip.
(circlip_28iw)

tests/SBR_rails.scad

@@ -0,0 +1,46 @@
+//
+// NopSCADlib Copyright Chris Palmer 2018
+// nop.head@gmail.com
+// hydraraptor.blogspot.com
+//
+// This file is part of NopSCADlib.
+//
+// NopSCADlib is free software: you can redistribute it and/or modify it under the terms of the
+// GNU General Public License as published by the Free Software Foundation, either version 3 of
+// the License, or (at your option) any later version.
+//
+// NopSCADlib is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+// without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+// See the GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along with NopSCADlib.
+// If not, see <https://www.gnu.org/licenses/>.
+//
+include <../core.scad>
+include <../vitamins/sbr_rails.scad>
+
+use <../utils/layout.scad>
+use <../vitamins/bearing_block.scad>
+
+length = 200;
+sheet = 3;
+
+module sbr_rails()
+    layout([for(r = sbr_rails) sbr_rail_base_width(r)], 10)
+        rotate([90, 180,0]) {
+            rail = sbr_rails[$i];
+            sbr_rail(rail, length);
+            carriage = sbr_rail_carriage(rail);
+            screw = sbr_rail_screw(rail);
+
+            sbr_bearing_block_assembly(carriage, sheet);
+
+            sbr_screw_positions(rail, length)
+                explode(20)
+                    rotate([90,0,0])
+                        screw(sbr_rail_screw(rail), 18);
+
+         }
+
+if($preview)
+    sbr_rails();

tests/bearing_blocks.scad

@@ -31,5 +31,16 @@ module scs_bearing_blocks()
                 scs_bearing_block_assembly(scs_bearing_blocks_long[$i - 1], part_thickness);
     }
 
-if($preview)
+module sbr_bearing_blocks()
+    layout([for(s = sbr_bearing_blocks) sbr_size(s).x], 10) {
+        part_thickness = 5;
+        sbr_bearing_block_assembly(sbr_bearing_blocks[$i], part_thickness);
+    }
+
+module bearing_blocks()
     scs_bearing_blocks();
+    translate([190,120,0])
+        sbr_bearing_blocks();
+
+if($preview)
+    bearing_blocks();

tests/linear_bearings.scad

@@ -28,6 +28,9 @@ module linear_bearings()
         translate([0, 30])
             linear_bearing(long_linear_bearings[$i]);
     }
+    layout([for(b = open_linear_bearings) 2 * bearing_radius(b)])
+        translate([105, 60])
+            linear_bearing(open_linear_bearings[$i]);
 
 if($preview)
     linear_bearings();