Drag chain ends can now be customised by adding children to the assembly.

printed/drag_chain.scad

@@ -23,12 +23,20 @@
 //! Each link has a maximum bend angle of 45°, so the mininium radius is proportional to the link length.
 //!
 //! The travel property is how far it can move in each direction, i.e. half the maximum travel if the chain is mounted in the middle of the travel.
+//!
+//! The ends can have screw lugs with four screw positions to choose from, specified by a list of two arrays of four bools.
+//! If none are enabled then a child object is expected to customise the end and this gets unioned with the blank end.
+//! If both ends are customised then two children are expected.
+//! Each child is called twice, once with ```$fasteners``` set to 0 to augment the STL and again with ```$fasteners``` set to 1 to add
+//! to the assembly, for example to add inserts.
 //
 
 include <../core.scad>
 use <../utils/horiholes.scad>
 use <../utils/maths.scad>
 
+clearance = 0.1;
+
 function drag_chain_name(type)        = type[0]; //! The name to allow more than one in a project
 function drag_chain_size(type)        = type[1]; //! The internal size and link length
 function drag_chain_travel(type)      = type[2]; //! X travel
@@ -38,6 +46,8 @@ function drag_chain_twall(type)       = type[5]; //! Top wall
 function drag_chain_screw(type)       = type[6]; //! Mounting screw for the ends
 function drag_chain_screw_lists(type) = type[7]; //! Two lists of four bools to say which screws positions are used
 
+function drag_chain_clearance() = clearance; //! Clearance around joints.
+
 function drag_chain_radius(type) = //! The bend radius at the pivot centres
     let(s = drag_chain_size(type))
         s.x / 2 / sin(360 / 16);
@@ -49,8 +59,6 @@ function drag_chain_z(type) = //! Outside dimension of a 180 bend
 function drag_chain(name, size, travel, wall = 1.6, bwall = 1.5, twall = 1.5, screw = M2_cap_screw, screw_lists = [[1,0,0,1],[1,0,0,1]]) = //! Constructor
     [name, size, travel, wall, bwall, twall, screw, screw_lists];
 
-clearance = 0.1;
-
 function drag_chain_outer_size(type) =     //! Link outer dimensions
     let(s = drag_chain_size(type), z = s.z + drag_chain_bwall(type) + drag_chain_twall(type))
         [s.x + z, s.y + 4 * drag_chain_wall(type) + 2 * clearance, z];
@@ -210,9 +218,12 @@ module drag_chain_link(type, start = false, end = false) { //! One link of the c
             translate([floor_x, -os.y / 2 + 0.5,  os.z - bwall])
                 cube([s.x - floor_x - clearance, os.y -1, bwall]);
 
-            if(start || end)
+            if(start || end) {
                 drag_chain_screw_positions(type, end)
                     screw_lug(drag_chain_screw(type), os.z);
+
+                children();
+            }
         }
         if(start || end)
             translate_z(-eps)
@@ -266,10 +277,17 @@ module drag_chain_assembly(type, pos = 0) { //! Drag chain assembly
     npoints = len(points);
 
     module link(n)                                  // Position and colour link with origin at the hinge hole
-        translate([-z / 2, 0, -z / 2])
+        translate([-z / 2, 0, -z / 2]) {
             stl_colour(n < 0 || n == npoints - 1 ? pp3_colour : n % 2 ? pp1_colour : pp2_colour)
-                drag_chain_link(type, start = n == -1, end = n == npoints - 1);
+                drag_chain_link(type, start = n == -1, end = n == npoints - 1)
+                    let($fasteners = 0) children();
+            let($fasteners = 1) children();
+        }
 
+    screws = drag_chain_screw_lists(type);
+    custom_start = screws[0] == [0, 0, 0, 0];
+    custom_end   = screws[1] == [0, 0, 0, 0];
+    assert($children == bool2int(custom_start) + bool2int(custom_end), "wrong number of children for end customisation");
     assembly(str(drag_chain_name(type), "_drag_chain")) {
         for(i = [0 : npoints - 2]) let(v = points[i+1] - points[i])
             translate(points[i])
@@ -277,10 +295,14 @@ module drag_chain_assembly(type, pos = 0) { //! Drag chain assembly
                     link(i);
 
         translate(points[0] - [x, 0, 0])
-            link(-1);
+            link(-1)
+                if(custom_start)
+                    children(0);
 
         translate(points[npoints - 1])
             hflip()
-                link(npoints - 1);
+                link(npoints - 1)
+                    if(custom_end)
+                        children(custom_start ? 1 : 0);
     }
 }

readme.md

@@ -4560,6 +4560,12 @@ Each link has a maximum bend angle of 45°, so the mininium radius is proport
 
 The travel property is how far it can move in each direction, i.e. half the maximum travel if the chain is mounted in the middle of the travel.
 
+The ends can have screw lugs with four screw positions to choose from, specified by a list of two arrays of four bools.
+If none are enabled then a child object is expected to customise the end and this gets unioned with the blank end.
+If both ends are customised then two children are expected.
+Each child is called twice, once with ```$fasteners``` set to 0 to augment the STL and again with ```$fasteners``` set to 1 to add
+to the assembly, for example to add inserts.
+
 
 [printed/drag_chain.scad](printed/drag_chain.scad) Implementation.
 
@@ -4581,6 +4587,7 @@ The travel property is how far it can move in each direction, i.e. half the maxi
 | Function | Description |
 |:--- |:--- |
 | ```drag_chain(name, size, travel, wall = 1.6, bwall = 1.5, twall = 1.5, screw = M2_cap_screw, screw_lists = [[1,0,0,1],[1,0,0,1]])``` | Constructor |
+| ```drag_chain_clearance()``` | Clearance around joints. |
 | ```drag_chain_outer_size(type)``` | Link outer dimensions |
 | ```drag_chain_radius(type)``` | The bend radius at the pivot centres |
 | ```drag_chain_z(type)``` | Outside dimension of a 180 bend |