diff --git a/src/turtle/_impl/_t3d_impl.scad b/src/turtle/_impl/_t3d_impl.scad
new file mode 100644
index 00000000..028a13ae
--- /dev/null
+++ b/src/turtle/_impl/_t3d_impl.scad
@@ -0,0 +1,161 @@
+function _t3d_x(pt) = pt[0];
+function _t3d_y(pt) = pt[1];
+function _t3d_z(pt) = pt[2];
+
+function _t3d_pt3D(x, y, z) = [x, y, z];
+
+function _t3d_create(pt, unit_vts) = 
+    [
+        is_undef(pt) ? _t3d_pt3D(0, 0, 0) : pt, 
+        is_undef(unit_vts) ? [_t3d_pt3D(1, 0, 0), _t3d_pt3D(0, 1, 0), _t3d_pt3D(0, 0, 1)] : unit_vts
+    ];
+
+function _t3d_plus(pt, n) = 
+    _t3d_pt3D(_t3d_x(pt) + n, _t3d_y(pt) + n, _t3d_z(pt) + n);
+function _t3d_minus(pt, n) = 
+    _t3d_pt3D(_t3d_x(pt) - n, _t3d_y(pt) - n, _t3d_z(pt) + n);
+function _t3d_mlt(pt, n) = 
+    _t3d_pt3D(_t3d_x(pt) * n, _t3d_y(pt) * n, _t3d_z(pt) * n);
+function _t3d_div(pt, n) = 
+    _t3d_pt3D(_t3d_x(pt) / n, _t3d_y(pt) / n, _t3d_z(pt) / n);
+function _t3d_neg(pt, n) = 
+    _t3d_mlt(pt, -1);
+
+function _t3d_ptPlus(pt1, pt2) = 
+    _t3d_pt3D(
+        _t3d_x(pt1) + _t3d_x(pt2), 
+        _t3d_y(pt1) + _t3d_y(pt2), 
+        _t3d_z(pt1) + _t3d_z(pt2)
+    );
+
+function _t3d_pt(turtle) = turtle[0];
+function _t3d_unit_vts(turtle) = turtle[1];
+
+// forward the turtle in the x' direction
+function _t3d_xu_forward(turtle, leng) = _t3d_create(
+    _t3d_ptPlus(_t3d_pt(turtle), _t3d_mlt(_t3d_unit_vts(turtle)[0], leng)),
+    _t3d_unit_vts(turtle)
+);
+
+// forward the turtle in the y' direction
+function _t3d_yu_forward(turtle, leng) = _t3d_create(
+    _t3d_ptPlus(_t3d_pt(turtle), _t3d_mlt(_t3d_unit_vts(turtle)[1], leng)),
+    _t3d_unit_vts(turtle)
+);
+
+// forward the turtle in the z' direction
+function _t3d_zu_forward(turtle, leng) = _t3d_create(
+    _t3d_ptPlus(
+        _t3d_pt(turtle), 
+        _t3d_mlt(_t3d_unit_vts(turtle)[2], leng)
+    ),
+    _t3d_unit_vts(turtle)
+);
+
+// turn the turtle around the x'-axis
+// return a new unit vector
+function _t3d_xu_turn(turtle, a) = 
+    let(cosa = cos(a), sina = sin(a))
+    _t3d_create(
+        _t3d_pt(turtle),
+        [
+            _t3d_unit_vts(turtle)[0], 
+            _t3d_ptPlus(
+                _t3d_mlt(_t3d_unit_vts(turtle)[1], cosa), 
+                _t3d_mlt(_t3d_unit_vts(turtle)[2], sina)
+            ), 
+            _t3d_ptPlus(
+                _t3d_mlt(_t3d_neg(_t3d_unit_vts(turtle)[1]), sina), 
+                _t3d_mlt(_t3d_unit_vts(turtle)[2], cosa)
+            )
+        ]
+    );
+
+// turn the turtle around the y'-axis
+// return a new unit vector
+function _t3d_yu_turn(turtle, a) = 
+    let(cosa = cos(a), sina = sin(a))
+    _t3d_create(
+        _t3d_pt(turtle),
+        [
+            _t3d_ptPlus(
+                _t3d_mlt(_t3d_unit_vts(turtle)[0], cosa), 
+                _t3d_mlt(_t3d_neg(_t3d_unit_vts(turtle)[2]), sina)
+            ),
+            _t3d_unit_vts(turtle)[1], 
+            _t3d_ptPlus(
+                _t3d_mlt(_t3d_unit_vts(turtle)[0], sina), 
+                _t3d_mlt(_t3d_unit_vts(turtle)[2], cosa)
+            )
+        ]
+    );
+
+// turn the turtle around the z'-axis
+// return a new unit vector
+function _t3d_zu_turn(turtle, a) = 
+    let(cosa = cos(a), sina = sin(a))
+    _t3d_create(
+        _t3d_pt(turtle),
+        [
+            _t3d_ptPlus(
+                _t3d_mlt(_t3d_unit_vts(turtle)[0], cosa), 
+                _t3d_mlt(_t3d_unit_vts(turtle)[1], sina)
+            ),
+            _t3d_ptPlus(
+                _t3d_mlt(_t3d_neg(_t3d_unit_vts(turtle)[0]), sina), 
+                _t3d_mlt(_t3d_unit_vts(turtle)[1], cosa)
+            ),
+            _t3d_unit_vts(turtle)[2], 
+        ]
+    );
+    
+function _t3d_set_point(t, point) = 
+    _t3d_create(point, _t3d_unit_vts(t));
+
+function _t3d_set_unit_vectors(t, unit_vectors) =
+    _t3d_create(_t3d_pt(t), unit_vectors);
+
+function _t3d_get(t, cmd) = 
+    cmd == "point" ? _t3d_pt(t) : 
+    cmd == "unit_vectors" ? _t3d_unit_vts(t) : 
+    assert(false, "unknown command");
+
+function _t3d_set(t, point, unit_vectors) = 
+    !is_undef(point) ? _t3d_set_point(t, point) :
+    !is_undef(unit_vectors) ? _t3d_set_unit_vectors(t, unit_vectors) :
+    assert(false, "no target to set");
+
+function _t3d_cmd(t, cmd, point, unit_vectors, leng, angle) = 
+    cmd == "xforward" ? _t3d_xu_forward(t, leng) : 
+    cmd == "yforward" ? _t3d_yu_forward(t, leng) : 
+    cmd == "zforward" ? _t3d_zu_forward(t, leng) : 
+    cmd == "xturn" ? _t3d_xu_turn(t, angle) : 
+    cmd == "yturn" ? _t3d_yu_turn(t, angle) : 
+    cmd == "zturn" ? _t3d_zu_turn(t, angle) : 
+    _t3d_get(t, cmd);
+
+function _t3d_cmdline(cmd, t, arg) = 
+    is_undef(arg) ? _t3d_get(t, cmd) : 
+    cmd == "xforward" ? _t3d_xu_forward(t, arg) : 
+    cmd == "yforward" ? _t3d_yu_forward(t, arg) : 
+    cmd == "zforward" ? _t3d_zu_forward(t, arg) : 
+    cmd == "xturn" ? _t3d_xu_turn(t, arg) : 
+    cmd == "yturn" ? _t3d_yu_turn(t, arg) : 
+    cmd == "zturn" ? _t3d_zu_turn(t, arg) : 
+    cmd == "point" ? _t3d_set_point(t, point) : 
+    cmd == "unit_vectors" ? _t3d_set_unit_vectors(t, unit_vectors) :  
+    assert(false, "unknown command");
+
+function _t3d_cmds(t, cmds, i = 0) = 
+    i == len(cmds) ? t :
+    let(
+        cmd = cmds[i][0],
+        arg = cmds[i][1]
+    )
+    _t3d_cmds(_t3d_cmdline(cmd, t, arg), cmds, i + 1);
+
+function _t3d_impl(t, cmd, point, unit_vectors, leng, angle) =
+    is_undef(t) ? _t3d_create(point, unit_vectors) :
+    is_undef(cmd) ? _t3d_set(t, point, unit_vectors) :
+    is_string(cmd) ? _t3d_cmd(t, cmd, point, unit_vectors, leng, angle) :
+                     _t3d_cmds(t, cmd);
\ No newline at end of file
diff --git a/src/turtle/t3d.scad b/src/turtle/t3d.scad
index 83235b4d..e136ed1b 100644
--- a/src/turtle/t3d.scad
+++ b/src/turtle/t3d.scad
@@ -8,164 +8,7 @@
 *
 **/ 
 
-function _t3d_x(pt) = pt[0];
-function _t3d_y(pt) = pt[1];
-function _t3d_z(pt) = pt[2];
-
-function _t3d_pt3D(x, y, z) = [x, y, z];
-
-function _t3d_create(pt, unit_vts) = 
-    [
-        is_undef(pt) ? _t3d_pt3D(0, 0, 0) : pt, 
-        is_undef(unit_vts) ? [_t3d_pt3D(1, 0, 0), _t3d_pt3D(0, 1, 0), _t3d_pt3D(0, 0, 1)] : unit_vts
-    ];
-
-function _t3d_plus(pt, n) = 
-    _t3d_pt3D(_t3d_x(pt) + n, _t3d_y(pt) + n, _t3d_z(pt) + n);
-function _t3d_minus(pt, n) = 
-    _t3d_pt3D(_t3d_x(pt) - n, _t3d_y(pt) - n, _t3d_z(pt) + n);
-function _t3d_mlt(pt, n) = 
-    _t3d_pt3D(_t3d_x(pt) * n, _t3d_y(pt) * n, _t3d_z(pt) * n);
-function _t3d_div(pt, n) = 
-    _t3d_pt3D(_t3d_x(pt) / n, _t3d_y(pt) / n, _t3d_z(pt) / n);
-function _t3d_neg(pt, n) = 
-    _t3d_mlt(pt, -1);
-
-function _t3d_ptPlus(pt1, pt2) = 
-    _t3d_pt3D(
-        _t3d_x(pt1) + _t3d_x(pt2), 
-        _t3d_y(pt1) + _t3d_y(pt2), 
-        _t3d_z(pt1) + _t3d_z(pt2)
-    );
-
-function _t3d_pt(turtle) = turtle[0];
-function _t3d_unit_vts(turtle) = turtle[1];
-
-// forward the turtle in the x' direction
-function _t3d_xu_forward(turtle, leng) = _t3d_create(
-    _t3d_ptPlus(_t3d_pt(turtle), _t3d_mlt(_t3d_unit_vts(turtle)[0], leng)),
-    _t3d_unit_vts(turtle)
-);
-
-// forward the turtle in the y' direction
-function _t3d_yu_forward(turtle, leng) = _t3d_create(
-    _t3d_ptPlus(_t3d_pt(turtle), _t3d_mlt(_t3d_unit_vts(turtle)[1], leng)),
-    _t3d_unit_vts(turtle)
-);
-
-// forward the turtle in the z' direction
-function _t3d_zu_forward(turtle, leng) = _t3d_create(
-    _t3d_ptPlus(
-        _t3d_pt(turtle), 
-        _t3d_mlt(_t3d_unit_vts(turtle)[2], leng)
-    ),
-    _t3d_unit_vts(turtle)
-);
-
-// turn the turtle around the x'-axis
-// return a new unit vector
-function _t3d_xu_turn(turtle, a) = 
-    let(cosa = cos(a), sina = sin(a))
-    _t3d_create(
-        _t3d_pt(turtle),
-        [
-            _t3d_unit_vts(turtle)[0], 
-            _t3d_ptPlus(
-                _t3d_mlt(_t3d_unit_vts(turtle)[1], cosa), 
-                _t3d_mlt(_t3d_unit_vts(turtle)[2], sina)
-            ), 
-            _t3d_ptPlus(
-                _t3d_mlt(_t3d_neg(_t3d_unit_vts(turtle)[1]), sina), 
-                _t3d_mlt(_t3d_unit_vts(turtle)[2], cosa)
-            )
-        ]
-    );
-
-// turn the turtle around the y'-axis
-// return a new unit vector
-function _t3d_yu_turn(turtle, a) = 
-    let(cosa = cos(a), sina = sin(a))
-    _t3d_create(
-        _t3d_pt(turtle),
-        [
-            _t3d_ptPlus(
-                _t3d_mlt(_t3d_unit_vts(turtle)[0], cosa), 
-                _t3d_mlt(_t3d_neg(_t3d_unit_vts(turtle)[2]), sina)
-            ),
-            _t3d_unit_vts(turtle)[1], 
-            _t3d_ptPlus(
-                _t3d_mlt(_t3d_unit_vts(turtle)[0], sina), 
-                _t3d_mlt(_t3d_unit_vts(turtle)[2], cosa)
-            )
-        ]
-    );
-
-// turn the turtle around the z'-axis
-// return a new unit vector
-function _t3d_zu_turn(turtle, a) = 
-    let(cosa = cos(a), sina = sin(a))
-    _t3d_create(
-        _t3d_pt(turtle),
-        [
-            _t3d_ptPlus(
-                _t3d_mlt(_t3d_unit_vts(turtle)[0], cosa), 
-                _t3d_mlt(_t3d_unit_vts(turtle)[1], sina)
-            ),
-            _t3d_ptPlus(
-                _t3d_mlt(_t3d_neg(_t3d_unit_vts(turtle)[0]), sina), 
-                _t3d_mlt(_t3d_unit_vts(turtle)[1], cosa)
-            ),
-            _t3d_unit_vts(turtle)[2], 
-        ]
-    );
-    
-function _t3d_set_point(t, point) = 
-    _t3d_create(point, _t3d_unit_vts(t));
-
-function _t3d_set_unit_vectors(t, unit_vectors) =
-    _t3d_create(_t3d_pt(t), unit_vectors);
-
-function _t3d_get(t, cmd) = 
-    cmd == "point" ? _t3d_pt(t) : 
-    cmd == "unit_vectors" ? _t3d_unit_vts(t) : 
-    assert(false, "unknown command");
-
-function _t3d_set(t, point, unit_vectors) = 
-    !is_undef(point) ? _t3d_set_point(t, point) :
-    !is_undef(unit_vectors) ? _t3d_set_unit_vectors(t, unit_vectors) :
-    assert(false, "no target to set");
-
-function _t3d_cmd(t, cmd, point, unit_vectors, leng, angle) = 
-    cmd == "xforward" ? _t3d_xu_forward(t, leng) : 
-    cmd == "yforward" ? _t3d_yu_forward(t, leng) : 
-    cmd == "zforward" ? _t3d_zu_forward(t, leng) : 
-    cmd == "xturn" ? _t3d_xu_turn(t, angle) : 
-    cmd == "yturn" ? _t3d_yu_turn(t, angle) : 
-    cmd == "zturn" ? _t3d_zu_turn(t, angle) : 
-    _t3d_get(t, cmd);
-
-function _t3d_cmdline(cmd, t, arg) = 
-    is_undef(arg) ? _t3d_get(t, cmd) : 
-    cmd == "xforward" ? _t3d_xu_forward(t, arg) : 
-    cmd == "yforward" ? _t3d_yu_forward(t, arg) : 
-    cmd == "zforward" ? _t3d_zu_forward(t, arg) : 
-    cmd == "xturn" ? _t3d_xu_turn(t, arg) : 
-    cmd == "yturn" ? _t3d_yu_turn(t, arg) : 
-    cmd == "zturn" ? _t3d_zu_turn(t, arg) : 
-    cmd == "point" ? _t3d_set_point(t, point) : 
-    cmd == "unit_vectors" ? _t3d_set_unit_vectors(t, unit_vectors) :  
-    assert(false, "unknown command");
-
-function _t3d_cmds(t, cmds, i = 0) = 
-    i == len(cmds) ? t :
-    let(
-        cmd = cmds[i][0],
-        arg = cmds[i][1]
-    )
-    _t3d_cmds(_t3d_cmdline(cmd, t, arg), cmds, i + 1);
+use <turtle/_impl/_t3d_impl.scad>;
 
 function t3d(t, cmd, point, unit_vectors, leng, angle) =
-    is_undef(t) ? _t3d_create(point, unit_vectors) :
-    is_undef(cmd) ? _t3d_set(t, point, unit_vectors) :
-    is_string(cmd) ? _t3d_cmd(t, cmd, point, unit_vectors, leng, angle) :
-                     _t3d_cmds(t, cmd);
\ No newline at end of file
+    _t3d_impl(t, cmd, point, unit_vectors, leng, angle);
\ No newline at end of file