diff --git a/src/turtle/_impl/_turtle3d_impl.scad b/src/turtle/_impl/_turtle3d_impl.scad
new file mode 100644
index 00000000..50f6ea88
--- /dev/null
+++ b/src/turtle/_impl/_turtle3d_impl.scad
@@ -0,0 +1,135 @@
+function _turtle3d_x(pt) = pt[0];
+function _turtle3d_y(pt) = pt[1];
+function _turtle3d_z(pt) = pt[2];
+
+function _turtle3d_pt3D(x, y, z) = [x, y, z];
+
+function _turtle3d_create(pt, unit_vts) = [pt, unit_vts];
+function _turtle3d_create_default() = _turtle3d_create(
+    _turtle3d_pt3D(0, 0, 0), 
+    // unit vectors from the turtle's viewpoint
+    [_turtle3d_pt3D(1, 0, 0), _turtle3d_pt3D(0, 1, 0), _turtle3d_pt3D(0, 0, 1)] 
+);
+
+function _turtle3d_plus(pt, n) = 
+    _turtle3d_pt3D(_turtle3d_x(pt) + n, _turtle3d_y(pt) + n, _turtle3d_z(pt) + n);
+function _turtle3d_minus(pt, n) = 
+    _turtle3d_pt3D(_turtle3d_x(pt) - n, _turtle3d_y(pt) - n, _turtle3d_z(pt) + n);
+function _turtle3d_mlt(pt, n) = 
+    _turtle3d_pt3D(_turtle3d_x(pt) * n, _turtle3d_y(pt) * n, _turtle3d_z(pt) * n);
+function _turtle3d_div(pt, n) = 
+    _turtle3d_pt3D(_turtle3d_x(pt) / n, _turtle3d_y(pt) / n, _turtle3d_z(pt) / n);
+function _turtle3d_neg(pt, n) = 
+    _turtle3d_mlt(pt, -1);
+
+function _turtle3d_ptPlus(pt1, pt2) = 
+    _turtle3d_pt3D(
+        _turtle3d_x(pt1) + _turtle3d_x(pt2), 
+        _turtle3d_y(pt1) + _turtle3d_y(pt2), 
+        _turtle3d_z(pt1) + _turtle3d_z(pt2)
+    );
+
+
+function _turtle3d_pt(turtle) = turtle[0];
+function _turtle3d_unit_vts(turtle) = turtle[1];
+
+// forward the turtle in the x' direction
+function _turtle3d_xu_move(turtle, leng) = _turtle3d_create(
+    _turtle3d_ptPlus(_turtle3d_pt(turtle), _turtle3d_mlt(_turtle3d_unit_vts(turtle)[0], leng)),
+    _turtle3d_unit_vts(turtle)
+);
+
+// forward the turtle in the y' direction
+function _turtle3d_yu_move(turtle, leng) = _turtle3d_create(
+    _turtle3d_ptPlus(_turtle3d_pt(turtle), _turtle3d_mlt(_turtle3d_unit_vts(turtle)[1], leng)),
+    _turtle3d_unit_vts(turtle)
+);
+
+// forward the turtle in the z' direction
+function _turtle3d_zu_move(turtle, leng) = _turtle3d_create(
+    _turtle3d_ptPlus(
+        _turtle3d_pt(turtle), 
+        _turtle3d_mlt(_turtle3d_unit_vts(turtle)[2], leng)
+    ),
+    _turtle3d_unit_vts(turtle)
+);
+
+// turn the turtle around the x'-axis
+// return a new unit vector
+function _turtle3d_xu_turn(turtle, a) = 
+    let(cosa = cos(a), sina = sin(a))
+    _turtle3d_create(
+        _turtle3d_pt(turtle),
+        [
+            _turtle3d_unit_vts(turtle)[0], 
+            _turtle3d_ptPlus(
+                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[1], cosa), 
+                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[2], sina)
+            ), 
+            _turtle3d_ptPlus(
+                _turtle3d_mlt(_turtle3d_neg(_turtle3d_unit_vts(turtle)[1]), sina), 
+                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[2], cosa)
+            )
+        ]
+    );
+
+// turn the turtle around the y'-axis
+// return a new unit vector
+function _turtle3d_yu_turn(turtle, a) = 
+    let(cosa = cos(a), sina = sin(a))
+    _turtle3d_create(
+        _turtle3d_pt(turtle),
+        [
+            _turtle3d_ptPlus(
+                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[0], cosa), 
+                _turtle3d_mlt(_turtle3d_neg(_turtle3d_unit_vts(turtle)[2]), sina)
+            ),
+            _turtle3d_unit_vts(turtle)[1], 
+            _turtle3d_ptPlus(
+                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[0], sina), 
+                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[2], cosa)
+            )
+        ]
+    );
+
+// turn the turtle around the z'-axis
+// return a new unit vector
+function _turtle3d_zu_turn(turtle, a) = 
+    let(cosa = cos(a), sina = sin(a))
+    _turtle3d_create(
+        _turtle3d_pt(turtle),
+        [
+            _turtle3d_ptPlus(
+                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[0], cosa), 
+                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[1], sina)
+            ),
+            _turtle3d_ptPlus(
+                _turtle3d_mlt(_turtle3d_neg(_turtle3d_unit_vts(turtle)[0]), sina), 
+                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[1], cosa)
+            ),
+            _turtle3d_unit_vts(turtle)[2], 
+        ]
+    );
+
+function _turtle3d_create_cmd(arg1, arg2) = 
+    is_undef(arg1) && is_undef(arg2) ? _turtle3d_create_default() : 
+    !is_undef(arg1) && !is_undef(arg2) ? _turtle3d_create(arg1, arg2) : undef;
+    
+function _turtle3d_chain_move(cmd, arg1, arg2) =
+    cmd == "xu_move" ? _turtle3d_xu_move(arg1, arg2) : 
+    cmd == "yu_move" ? _turtle3d_yu_move(arg1, arg2) : 
+    cmd == "zu_move" ? _turtle3d_zu_move(arg1, arg2) : _turtle3d_chain_turn(cmd, arg1, arg2);
+    
+function _turtle3d_chain_turn(cmd, arg1, arg2) = 
+    cmd == "xu_turn" ? _turtle3d_xu_turn(arg1, arg2) : 
+    cmd == "yu_turn" ? _turtle3d_yu_turn(arg1, arg2) : 
+    cmd == "zu_turn" ? _turtle3d_zu_turn(arg1, arg2) : _turtle3d_chain_one_arg(cmd, arg1);    
+
+function _turtle3d_chain_one_arg(cmd, arg) = 
+    cmd == "pt" ? _turtle3d_pt(arg) : 
+    cmd == "unit_vts" ? _turtle3d_unit_vts(arg) : undef;
+    
+function _turtle3d_impl(cmd, arg1, arg2) =
+    cmd == "create" ? 
+        _turtle3d_create_cmd(arg1, arg2) : 
+        _turtle3d_chain_move(cmd, arg1, arg2);    
\ No newline at end of file
diff --git a/src/turtle/turtle3d.scad b/src/turtle/turtle3d.scad
index ca5866ee..3e566069 100644
--- a/src/turtle/turtle3d.scad
+++ b/src/turtle/turtle3d.scad
@@ -8,138 +8,6 @@
 *
 **/ 
 
-function _turtle3d_x(pt) = pt[0];
-function _turtle3d_y(pt) = pt[1];
-function _turtle3d_z(pt) = pt[2];
-
-function _turtle3d_pt3D(x, y, z) = [x, y, z];
-
-function _turtle3d_create(pt, unit_vts) = [pt, unit_vts];
-function _turtle3d_create_default() = _turtle3d_create(
-    _turtle3d_pt3D(0, 0, 0), 
-    // unit vectors from the turtle's viewpoint
-    [_turtle3d_pt3D(1, 0, 0), _turtle3d_pt3D(0, 1, 0), _turtle3d_pt3D(0, 0, 1)] 
-);
-
-function _turtle3d_plus(pt, n) = 
-    _turtle3d_pt3D(_turtle3d_x(pt) + n, _turtle3d_y(pt) + n, _turtle3d_z(pt) + n);
-function _turtle3d_minus(pt, n) = 
-    _turtle3d_pt3D(_turtle3d_x(pt) - n, _turtle3d_y(pt) - n, _turtle3d_z(pt) + n);
-function _turtle3d_mlt(pt, n) = 
-    _turtle3d_pt3D(_turtle3d_x(pt) * n, _turtle3d_y(pt) * n, _turtle3d_z(pt) * n);
-function _turtle3d_div(pt, n) = 
-    _turtle3d_pt3D(_turtle3d_x(pt) / n, _turtle3d_y(pt) / n, _turtle3d_z(pt) / n);
-function _turtle3d_neg(pt, n) = 
-    _turtle3d_mlt(pt, -1);
-
-function _turtle3d_ptPlus(pt1, pt2) = 
-    _turtle3d_pt3D(
-        _turtle3d_x(pt1) + _turtle3d_x(pt2), 
-        _turtle3d_y(pt1) + _turtle3d_y(pt2), 
-        _turtle3d_z(pt1) + _turtle3d_z(pt2)
-    );
-
-
-function _turtle3d_pt(turtle) = turtle[0];
-function _turtle3d_unit_vts(turtle) = turtle[1];
-
-// forward the turtle in the x' direction
-function _turtle3d_xu_move(turtle, leng) = _turtle3d_create(
-    _turtle3d_ptPlus(_turtle3d_pt(turtle), _turtle3d_mlt(_turtle3d_unit_vts(turtle)[0], leng)),
-    _turtle3d_unit_vts(turtle)
-);
-
-// forward the turtle in the y' direction
-function _turtle3d_yu_move(turtle, leng) = _turtle3d_create(
-    _turtle3d_ptPlus(_turtle3d_pt(turtle), _turtle3d_mlt(_turtle3d_unit_vts(turtle)[1], leng)),
-    _turtle3d_unit_vts(turtle)
-);
-
-// forward the turtle in the z' direction
-function _turtle3d_zu_move(turtle, leng) = _turtle3d_create(
-    _turtle3d_ptPlus(
-        _turtle3d_pt(turtle), 
-        _turtle3d_mlt(_turtle3d_unit_vts(turtle)[2], leng)
-    ),
-    _turtle3d_unit_vts(turtle)
-);
-
-// turn the turtle around the x'-axis
-// return a new unit vector
-function _turtle3d_xu_turn(turtle, a) = 
-    let(cosa = cos(a), sina = sin(a))
-    _turtle3d_create(
-        _turtle3d_pt(turtle),
-        [
-            _turtle3d_unit_vts(turtle)[0], 
-            _turtle3d_ptPlus(
-                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[1], cosa), 
-                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[2], sina)
-            ), 
-            _turtle3d_ptPlus(
-                _turtle3d_mlt(_turtle3d_neg(_turtle3d_unit_vts(turtle)[1]), sina), 
-                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[2], cosa)
-            )
-        ]
-    );
-
-// turn the turtle around the y'-axis
-// return a new unit vector
-function _turtle3d_yu_turn(turtle, a) = 
-    let(cosa = cos(a), sina = sin(a))
-    _turtle3d_create(
-        _turtle3d_pt(turtle),
-        [
-            _turtle3d_ptPlus(
-                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[0], cosa), 
-                _turtle3d_mlt(_turtle3d_neg(_turtle3d_unit_vts(turtle)[2]), sina)
-            ),
-            _turtle3d_unit_vts(turtle)[1], 
-            _turtle3d_ptPlus(
-                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[0], sina), 
-                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[2], cosa)
-            )
-        ]
-    );
-
-// turn the turtle around the z'-axis
-// return a new unit vector
-function _turtle3d_zu_turn(turtle, a) = 
-    let(cosa = cos(a), sina = sin(a))
-    _turtle3d_create(
-        _turtle3d_pt(turtle),
-        [
-            _turtle3d_ptPlus(
-                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[0], cosa), 
-                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[1], sina)
-            ),
-            _turtle3d_ptPlus(
-                _turtle3d_mlt(_turtle3d_neg(_turtle3d_unit_vts(turtle)[0]), sina), 
-                _turtle3d_mlt(_turtle3d_unit_vts(turtle)[1], cosa)
-            ),
-            _turtle3d_unit_vts(turtle)[2], 
-        ]
-    );
-
-function _turtle3d_create_cmd(arg1, arg2) = 
-    is_undef(arg1) && is_undef(arg2) ? _turtle3d_create_default() : 
-    !is_undef(arg1) && !is_undef(arg2) ? _turtle3d_create(arg1, arg2) : undef;
+use <turtle/_impl/_turtle3d_impl.scad>;
     
-function _turtle3d_chain_move(cmd, arg1, arg2) =
-    cmd == "xu_move" ? _turtle3d_xu_move(arg1, arg2) : 
-    cmd == "yu_move" ? _turtle3d_yu_move(arg1, arg2) : 
-    cmd == "zu_move" ? _turtle3d_zu_move(arg1, arg2) : _turtle3d_chain_turn(cmd, arg1, arg2);
-    
-function _turtle3d_chain_turn(cmd, arg1, arg2) = 
-    cmd == "xu_turn" ? _turtle3d_xu_turn(arg1, arg2) : 
-    cmd == "yu_turn" ? _turtle3d_yu_turn(arg1, arg2) : 
-    cmd == "zu_turn" ? _turtle3d_zu_turn(arg1, arg2) : _turtle3d_chain_one_arg(cmd, arg1);    
-
-function _turtle3d_chain_one_arg(cmd, arg) = 
-    cmd == "pt" ? _turtle3d_pt(arg) : 
-    cmd == "unit_vts" ? _turtle3d_unit_vts(arg) : undef;
-    
-function turtle3d(cmd, arg1, arg2) =
-    cmd == "create" ? 
-        _turtle3d_create_cmd(arg1, arg2) : 
-        _turtle3d_chain_move(cmd, arg1, arg2);    
\ No newline at end of file
+function turtle3d(cmd, arg1, arg2) = _turtle3d_impl(cmd, arg1, arg2);    
\ No newline at end of file