This pachinko-style slot machine accumulates pennies until one goes bouncing though the middle slot, and then Ka-ching!, all your cash gets released back into the payoff tray. You only need about 20 cents to play.

This is designed for US pennies (19.05mm dia x 1.52mm thick) but you should be able to scale it up or down slightly for different sized coins, or even for flat washers.

Note: The cover appears as a solid, opaque part, but if you look at the 3MF file settings, it is printed with zero top and bottom layers and an infill of about ~10%. This creates a nice see-thru grill. Feel free to try different infill patterns and densities to get different effects.

Game Play

While it is entertaining enough to put your money, watch it bounce around, and then eventually get it all back, this actually makes for a great multi-player game. Just take turns with one or more friends putting in one coin per turn. The odds build up over time that someone will hit the jackpot.

Assembly
To assemble, you will need 4 short pieces (about 12mm long) of 1.75mm dia. filament to act as pivot pins. These pieces should press firmly into the right and left side gate and latch pieces as shown in the photos below. To start out with they should be pushed flush with the top side of these pieces and stick out some on the back sides.

Next, the gate piece (that looks like a bird) gets assembled into the upper hole on one side as shown below. The gate is gravity operated and needs to be able to flop down under its own weight. If holes in the pachinko boards are a little too tight, stick longer piece of filament (or similarly sized tool) through the hole and work it around to enlarge it slightly until the gate moves completely freely. 

The filament pin sticking out the back side of the pachinko board needs to be cut off perfectly flush. You can do this with flush-cutting side-cutters, but if you can't get the pins completely flush, use a razor blade or Xacto knife to trim them flush. (Below I've shown the pins in a contrasting color for clarity.)

Then put the latch piece on to through the lower hole. Make sure the gate pivots effortlessly as well. Trim it as well.  side.

Repeat the steps above for the other side:

Now slide the pachinko board in base intil fully seated:

Lastly, install the cover grill. It should lightly press into place: