My living group participates in a Secret Santa tradition where no money may be spent on gifts. I had plenty of scrap wood around, and got inspired by seeing other mason jar gumball machines. I decided to try making one with a mechanical twist.

I started with a quart-sized mason jar and dimensioned the dispenser around it. Any other size will work, so long as the ratios remain similar.

Without the mason jar, the dispenser is approximately 8" tall and has a 5x5" footprint.

I forgot to take enough in-progress photos when creating this dispenser, so I created a supplementary CAD model to help explain some of the steps.

Step 1: Tools & Materials

I used the following materials:

one quart-size mason jar with sealing lid (example internet photos above)
scrap wood, including a piece of 4x4 4" long, two pieces of 1.2" thick pine board measuring 5x5" each, one piece of 3/4" thick wood measuring at least 3.5x3.5", and four pieces of 3/8" thick plywood measuring at least 4x4"
one 1/2" dowel, at least 1.5" long
three .18" steel dowel pins (example internet photo above)
six 3/16" flat washers
one 1-1/4" wood screw
wood glue and superglue
wood stain and finish
candy!

And the following tools:

A miter chop saw (with effort, hand saws will work as well)
power drill for holes
scroll saw (a laser cutter didn't work for me, but would expedite the process)
hole cutter (to save time cutting 3" diameter holes)
sandpaper, 220 grit
Solidworks, a CAD program that made planning this project so much easier

Step 2: Beginning Sketches and Gear Math

To build the dispensing system I decided to use a rotating spur gear with a cutout to carry candy. I also wanted to add two more gears to make room for a handle and to make it more interesting.

I decided on 4", 3", and 2" diameters for the gears but didn't really care about number of teeth or other parameters.

To figure those out, I used the following formula: P = (N+2)/D,
where P is the diametrial pitch, N is # of teeth, and D is the outer diameter I want.

There's also pressure angle, which determines the curvature of the tooth.The below pictures show how a gear (original at top left) changes with different pitch, teeth, and pressure angle respectively.

In order for gears to mesh, they must have the same pitch. I picked 6 teeth-per-inch (the smallest pitch in Solidworks' dropdown menu that worked for my outer diameters). For real (power transmitting) gears, you shouldn't have fewer than 12 teeth, but since I don't need my gears to be efficient I was okay with having my smallest gear be a 6-tooth.

I had Solidworks generate drawings for me, but any online gear profile generator will work as well. The center holes are 3/16" to fit my dowels. (My drawings also include cutouts for candy and a pilot hole for screwing on a handle)

Once I had proper gear drawings, I followed this guide for cutting them out with a scroll saw. (I first tried having a lasercutter cut them for me, but it gave me charcoal instead.) Don't worry if your cuts aren't perfect; you can file off any sticking spots when you pin the gears in place. If you're printing out gear templates, make sure they're at the proper scale!

Because I originally tried to lasercut my gears, I used 3/8" ply. I felt that this was too thin for my largest gear, so I glued two pieces together to double the thickness. (Your thickness and cutout should be big enough to accommodate your candy) Sand the teeth smooth.

If you want, stain and finish your gears. Set these aside while you work on the base.

Screw on a dowel to your medium-sized gear for a handle. (Mine was 1.5" long)

Step 3: Constructing the Base

Cut all your wood to size, then take your 4x4 and glue it to the center of one 5x5" board. This is the bottom part of your base.

While that is drying, cut a hole in the center of the other 5x5" board. The hole should be big enough to snugly fit the mason jar cap (3" diameter in my case). Then, drill a 3/16" hole as close as possible to the hole you just made, approximately 2/3 the length of the steel dowel pin. The pin should be loose. Place your thinner piece of wood in the center of this assembly and cut out space for the gear. Remove the gear and glue the insert onto the board. This is the cap.

Align your bottom and cap so that the 4x4 pieces match, and mark where the pin hole should be. This hole should be 1/3 to 1/2 the length of the pin. Fit a washer and your large gear onto the pin and make sure the large gear's cutout reaches the jar hole and outside, but not both at once (don't spill the candy!)

Put a washer on top of the gear and fit the cap back on. Make sure your gear still spins freely. Then glue bottom and cap together. Once the glue dried, I sanded everything smooth and added wood stain.

Congrats, you're finished with the hard part!

Step 4: Fitting Gears and Completing the Base

First, without drilling any holes, position each gear such that it meshes (if you rotate it, the other spins freely) and mark the corresponding pin holes. Drill holes deep enough so that the pins extend no more than 1/4" past the gears. Then superglue (or woodglue, if you feel like waiting) the pins in place. Add washers and gears. I capped the pins with short nubs of dowel to match the handle.

Glue the mason jar lid so that its bevel rests on top of the cap. Make sure the lid is level and doesn't interfere with your gears. Let dry.

While constructing this, I discovered that the skittles I was using weren't round enough to roll to the dispensing gear on their own, so I made a sloped insert by taking a leftover piece of plywood and shaving off an angle.

Step 5: Putting Everything Together!

Once everything is dry, attach the mason jar by flipping your base upside-down and screwing your parts together.

If any candy is in the jar, make sure your dispensing gear is rotated so that candy won't spill when you flip it back over!

Step 6: Thanks

Again, I apologize for forgetting to take actual in-progress photos. I'm hoping to make up for it by including the CAD reconstruction files and gear DXF (mason jar courtesy of Daniel Flores from GrabCAD)

If I make this again I'd add a sloped tongue, or make the cutout stick out further, so that users don't have to hold their hands flush to the base to catch all the candy. It's a little awkward if you have large hands.

Thanks for taking a look! Read about this and more on my blog, http://ava-makes-things.blogspot.com/