Desk Toy - How to Build a Mini Gumball Machine

Hello, I'm Brandon Chang, a 4th-year mechanical engineering student at San Jose State University and a member of my university's ASME club.

In this instructable, I will give a general overview of how I designed my mini gumball machine and the steps for printing parts and ultimately assembling my version of a mini gumball machine. This project utilized 3D printing as its means of fabrication, and all parts were designed entirely within the Fusion 360 workspace.

The inspiration for this project originated from my wanting an interactive desk toy that could be displayed in an office space and is fun for people to use.

To start your mini gumball machine project, you will need the tools & supplies listed below.

I recommend taking a trip to your local hardware store to find the required fasteners before resorting to online purchases. For people reading this instructable outside of North America, some specialty hardware stores in your local area may carry imperial and metric style fasteners that you can buy by the piece instead of buying a whole box of fasteners online.

Hardware & Tools:

• 3D printer or access to 3D printing services
• Metric hex key tool or key set
• 3/32in. hex key
• Super glue
• Fasteners from the local hardware store:
• 1 x 1/4in. Shaft Collar
• 1 x 1/4in. X 5 1/2in. carriage bolt
• 4 x 1/8in. X 1/2in. steel dowel pins
• 4 x M3 X 8mm machine screws
• 4 x M3 hex nuts
• 2 x M4 hex nuts
• 2 x M4 x 3mm set screws
• [Optional] Sandpaper (120, 220, 320, 800, and 1500 grit)
• [Optional] 1/4in. coarse-thread tap ***I highly recommend using this to clean up 3D printed threads

3D Printed Bill-Of-Materials:

• 556g of your filament of choice (You can ignore this if you choose to use a 3D printing service)
• 1 x Gumball Handle
• 1 x Gumball Lid
• 1 x Gumball Bowl
• 1 x Gumball Sweeper Arm
• 1 x Gumball Body
• 1 x Gumball Catcher
• 1 x Gumball Hopper Lid
• 1 x Gumball Hopper Funnel
• 1 x Gumball Slide Stand
• 1 x Gumball Door
• 1 x Gumball Door Hinge Pin

***If you would like to start printing right away, skip to Step 4: Slicing & Printing The Gumball Machine

When initially considering how I wanted to make this mini gumball machine, my three primary design focuses were :

1. Size
2. Ease of Assembly
3. Dispensing Mechanism

Size

The build plate/size of the 3D printer will determine the size of the gumball machine you may design. The printer I use has an 8.7in. x 8.7in. (220mm x 220mm) build plate, so I kept this in mind while working my way through the design.

My thought process was to use this build plate constraint as a guide when determining the size of the gumball bowl and leave enough room in the design to build up more significant parts around it. By starting with a smaller 5in. diameter gumball bowl, I could quickly iterate the rest of my components until I was happy with the form taking shape and then begin to add in more details & features.

Ease of Assembly

Adding fasteners, embedded hex nuts, keyed joints, and other valuable features to 3D printed parts are essential to making your life easier when it comes time to assemble your design. In addition, using off-the-shelf screws & nuts helps to extend the life of your 3D printed designs by overcoming the limitations of FDM printed parts regarding repeated assembly and disassembly.

A simple press-fit holds the hex nuts used in the gumball bowl and the gumball sweeper. It's not necessary, but for extra hold, you can add a dab of super glue when press-fitting the hex nuts into those parts.

The tiny door shown in the picture above uses a built-in keyway in its hinge that takes a keyed hinge pin shown to its side. If the door or pin should ever wear out, it's an easy replacement that only consumes about five grams of filament at 20% infill to replace both of them.

Dispensing Mechanism

The gumballs I chose to use are about 1/2in. diameter, so any holes I added to the design need to be at least 1/2in. or larger to allow the gumballs to easily move through the mini gumball machine.

My mini gumball dispensing mechanism consists of static input and output plates with offset holes in my design. A rotating catching plate is positioned between the stationary plates to transport one gumball at a time between the input and the output. The catching plate uses a carriage bolt to lock the rotation of the plate to the bolt.

A sweeping arm is attached to the carriage bolt above the stationary input plate to agitate the gumballs inside the bowl as the user spins the handle. This sweeping will help the gumballs not get stuck when competing to fall into the catching plate.

To generate the gcode for the 3D printer to read, you will need slicing software such as Ultimaker Cura, PrusaSlicer, or some other slicer to slice the attached .stl files.

I sliced my parts in Cura with the stock Cura settings for PLA at 0.2mm layer height and 20% infill. All the pieces can be printed without supports, except for the hinge pin and gumball bowl, for which I used tree supports.

My overall print time for all the parts was about 60 hours & 12 minutes, split between four different prints on an Ender 3 Pro and another Ender 3. This entire project only requires about 556 grams of filament to print all the required components.

The mini gumball machine consists of 5 sub-assemblies, a shaft collar, and a handle:

1. Gumball Body
2. 4 x 1/8in. dowel pins
3. Insert dowel pins into holes on the top face of the gumball body.
4. Gumball Stand
5. Gumball Funnel
6. Gumball Funnel Lid
7. Superglue funnel and lid together.
8. Superglue combined funnel to gumball stand in the configuration shown in the image above.
9. Gumball Catching Plate
10. Carriage Bolt
11. Insert carriage bolt into catching plate and superglue in place.
12. Gumball Bowl
13. Gumball Lid
14. 4 x M3 hex nuts
15. 4 x M3 screws
16. Press-fit hex nuts into recesses on the top lip of the bowl and optionally superglue in place.
17. Line up gumball lid with hex nuts and screw into place.
18. Gumball Sweeper
19. 2 x M4 hex nuts
20. 2 x M4 set screws
21. Insert hex nuts into recesses with the point of the hex down.

Once fully assembled, to quickly fill the gumball machine, you start by removing the handle and shaft collar. With the gumball bowl loose, invert the bowl, and fill it with gumballs or other 1/2in. diameter candy. With the gumball bowl filled, insert the assembly into the inverted bowl until flush, turn upright, and reattach the shaft collar & handle to complete the assembly.

If you've finished all the steps up until now, congratulations!

You now have a mini gumball machine you can proudly display in your office or home, enjoy sending gumballs down the slide to knock the tiny door open.