1 old ball mouse
1 peanut butter lid (yes, really)
a bunch of small coins
some old Legos:
-1 four or six-peg axle
-2 small right-angle gears
-1 large wheel
-some spacer bits
Step 1: Cheap Spinner Interface
Just cut out the bare parts you need. That means keep the plastic that holds the encoder shaft in place, and try to leave enough extra to support the electronic bits. It doesn't hurt to have a good flat area to glue the whole thing down with either.
Step 2: Attach the Shaft Gear
Stick the gear on the shaft, leaving enough room for the mating gear. The tricky part is to keep the gear centered on the shaft. If you spin it while the glue is setting, you can tell what parts are off and gently correct them.
Step 3: Add The Electronic Bits
Use a razor blade or rotary tool to relocate the section of circuit board with the optical parts. This helps ensure they're the same distance apart as they are meant to be, which turns out to be pretty crucial. Then use a few wires to solder the points back together. Finally, glue the whole thing down, taking care to keep everything aligned. You can leave the mouse plugged in while you do this to make sure that everything stays lined up.
Just be sure not to have the sun streaming in like I did, since that throws everything off.
Step 4: Make Spinners Better
Lay down some pennies in the wheel before gluing to visualize the spacing. Glue them down in a star pattern to help keep the spacing even. Hot glue will let you stack 2 layers of pennies, super glue should be thin enough to stack 3. Fill up both sides for more weight.
Step 5: Glue on the Lid
Put a ring of hot melt glue around the wheel, and stick the wheel in the lid. While the glue's hot, stick a few dimes in between the wheel and the lid to help keep everything centered.
Step 6: Paddle Assembly
Step 7: Paddle Installation
I used a couple scraps of MDF as a platform for the mouse parts.
If you keep the mouse plugged in while you install the paddles, you can make sure everything stays working as the glue sets.
One great thing about hot glue is that you can sort of control the working time of it by varying the temperature of the glue gun.