diff --git a/holodisk.scad b/holodisk.scad
index 3745bd1..882f490 100755
--- a/holodisk.scad
+++ b/holodisk.scad
@@ -7,6 +7,7 @@ use <holodisk_spec.scad>
 use <anim.scad>
 
 include <tape.scad>
+use <tape_spool.scad>
 
 disk_size = get_holodisk_size();
 holodisk_size = get_holodisk_size();
@@ -235,7 +236,7 @@ module frame(size) {
         module laserwindow_slider_cover() {
             cover_size=[
                 get_holodisk_laserwindow_size().x,
-                rails_size.y + overlap*2,
+                get_holodisk_slide_slider_size().x,
                 get_holodisk_slide_slider_size().z
             ];
             cover_plate=[cover_size.x, rail_size.y, cover_size.z];
@@ -247,7 +248,7 @@ module frame(size) {
             translate(cover_pos)
             hull() {
                 fwd(cover_plate.y) cube(cover_plate);
-                fwd(cover_top.y) up((cover_plate.z-cover_top.z)/2) cube(cover_top);
+                right(overlap/2) fwd(cover_top.y) up((cover_plate.z-cover_top.z)/2) cube(cover_top);
             }
         }
         
@@ -270,52 +271,19 @@ module mechanism(size) {
     depth=size.y;
     height=size.z;
     
-    module spool(r_in, r_out, in_rim, out_rim) {
-        module spindle(d, h) {
-            color("Sienna") cylinder(h=h, d=d);
-        }
-            
-        module spool_plate() {
-            difference() {
-                cylinder(h=spool_plate_height, r=r_out);
-                if (!$preview && r_out - r_in > out_rim) {
-                    angle=spool_plate_hole_angle;
-                    difference() {
-                        for (i = [1:spool_plate_holes]) {
-                            zrot(360/spool_plate_holes * i) {
-                                angle_pie_mask(r=r_out - out_rim, l=spool_plate_height, ang=angle, center=false);
-                            }
-                        }
-                        cylinder(h=spool_plate_height, r=r_in + in_rim);
-                    }
-                }
-            }
-        }
-        
-        spindle_h=height-plate;
-        difference() {
-            color("Azure") {
-                spool_plate();
-                up(spool_plate_height) cylinder(h=spool_inner_height, r=r_in);
-                up(spool_plate_height + spool_inner_height) spool_plate();
-            }
-            up(spool_plate_height + spool_inner_height/2) cube([r_in*2, spool_slit_depth, spool_inner_height], center=true);
-            // TODO: spindle height
-            spindle(d=spindle_diam+spindle_diam_tolerance, h=spindle_h);
-        }
-        spindle(d=spindle_diam, h=spindle_h);
-    }
-    
     module main_spool() {
         spool(r_in=spool_inner_radius,
             r_out=spool_outer_radius,
             in_rim=spool_plate_hole_inner_rim,
-            out_rim=spool_plate_hole_outer_rim);
+            out_rim=spool_plate_hole_outer_rim,
+            in_height=spool_inner_height);
     }
     module aux_spool() {
         spool(r_in=middle_spool_in_r, r_out=middle_spool_out_r,
             in_rim=aux_spool_plate_hole_inner_rim,
-            out_rim=aux_spool_plate_hole_outer_rim);
+            out_rim=aux_spool_plate_hole_outer_rim,
+            in_height=spool_inner_height,
+            spokes=4);
     }
     
     module spools() {
diff --git a/tape_spool.scad b/tape_spool.scad
new file mode 100644
index 0000000..09a4af8
--- /dev/null
+++ b/tape_spool.scad
@@ -0,0 +1,82 @@
+spool_tape_tolerance=1;
+spool_inner_radius=4;
+spool_outer_radius=18;
+spool_plate_height=2;
+spool_plate_holes=3;
+spool_plate_hole_angle=360/spool_plate_holes * 0.5;
+spool_plate_hole_inner_rim=1;
+spool_plate_hole_outer_rim=4;
+spindle_diam_tolerance=0.2;
+
+// dependency: https://github.com/revarbat/BOSL
+use <BOSL/transforms.scad>
+
+module spindle(d, h, traction=false) {
+    color("Sienna") cylinder(h=h, d=d, $fn=(traction ? 6 : 20));
+}
+
+module spool(
+        r_in, r_out,
+        in_rim=1, out_rim=4,
+        in_height=5, plate_height=1,
+        center=false, slit_depth=0.5,
+        spindle_diam=3, spindle_diam_tolerance=0.1, spindle_traction=false,
+        spokes=3
+        ) {
+    height = plate_height*2 + in_height;
+    tape_height=in_height;
+    module spool_plate() {
+        $fn = ($preview ? 18 : 100);
+        if (/*!$preview &&*/ spokes > 0 && r_out - r_in > out_rim) {
+            union() {
+                cylinder(h=plate_height, r=r_in + in_rim);
+                intersection() {
+                    cylinder(h=plate_height, r=r_out - out_rim);
+                    for (i = [1:spokes]) {
+                        zrot(360/spokes * i) {
+                            right(r_out/2) up(plate_height/2)
+                            cube([r_out, r_in, plate_height], center=true);
+                        }
+                    }
+                    
+                }
+                difference() {
+                    cylinder(h=plate_height, r=r_out);
+                    cylinder(h=plate_height, r=r_out - out_rim);
+                }
+            }
+        } else {
+            cylinder(h=plate_height, r=r_out);
+        }
+    }
+    
+    module spool_inner() {
+        $fn = ($preview ? 10 : 60);
+        cylinder(h=in_height, r=r_in);
+    }
+    
+    down(center ? height/2 : 0)
+    difference() {
+        color("Azure") {
+            spool_plate();
+            up(plate_height) spool_inner();
+            up(plate_height + in_height) spool_plate();
+        }
+        if (slit_depth > 0) {
+            up(plate_height + in_height/2) cube([r_in*2, slit_depth, in_height], center=true);
+        }
+        down(height) scale(1 + spindle_diam_tolerance/spindle_diam) spindle(d=spindle_diam+spindle_diam_tolerance, h=height*3, traction=spindle_traction);
+    }
+}
+
+module spool_spindle() {
+    spindle_h=height-plate;
+    spindle(d=spindle_diam, h=spindle_h);
+}
+
+// test
+spindle_diam=2;
+tape_height=5;
+traction=true;
+spool(r_in=4, r_out=20, in_height=tape_height, spindle_diam=spindle_diam, spindle_traction=traction);
+down(3) spindle(d=spindle_diam, h=tape_height + 8, traction=traction);
\ No newline at end of file