Well, I had a great time building gifts for Christmas this year, and at least one of the gifts I built was enough fun that I thought I would share it here at Instructables.

Away at college, my son has become quite a dedicated Dungeon Master, and he obviously has way too many dice -- but that would never stop him from wanting more dice, of course. He told me about an oversized "D20 of Doom" which (he says) he has seen in real life which is about the size of a basketball which would be used when someone does something really stupid during a campaign. I looked for something like that at Amazon, and of course, from my point of view that sort of thing should not cost more than $20, but it does not. Seriously.

Quick tips for this project:

I used my Silhouette Cameo cutter to cut all my paper, but if you print the templates I have included in this Instructable I am 100% sure you can use a utility knife and a straight edge to cut out what needs to be cut.
I used super glue, 2-part quick set epoxy, card stock paper, large foam sheets, the generic branded vinyl from H****L**** (insert craft store supplier here) to get the most robust version of this project. You could probably not add the foam and vinyl, buy precut numbers, and still drag this project in at under $10. I spent about $18.
You can upgrade this project by using heavier card stock, or for the very hard-core builder constructing the body of the Icosahedron (20-sided polyhedron) out of hobby shop sheet plastic. However, there comes a point at which what you gain in durability you give up in cost-consciousness. You do what makes you happy as you build this project!

Let's get started!

Supplies

2 small tubes of super glue
2 tubes 1 oz quick set 2-part epoxy (Optional if you are not overlaminating your project with foam)
- 7-10 disposable shop brushes to use for glue application
1 sheet 5mm craft foam (12x18 - you choose the color) (Optional if you are not overlaminating your project with foam)
3 sheets 12x12 card stock (you choose the color)
- ProTip: if you don't have a Cricut or a Cameo and you are cutting by hand, your paper size has to match the size of paper you can feed through your printer
1 sheet permanent-stick vinyl (you choose the color)
- Alternative: if you don't have a Cricut or a Cameo, buy a pack of permanent-stick precut numbers from your craft store or an office supply store.
Sharp craft utility knife, spare blades
masking tape
(optional) a lunch bag full of shredded paper

Step 1: Basic Shape Design

I had quite an argument with my daughter about whether or not it's even possible to do this project, but age and guile beat youth and a stylish haircut every time. So here is the thing: the most-basic version of this project is made by cutting out 2 identical versions of the same 10-sided paper model parts. In the BLUE image above (taken from my Silhouette Studio software) is the measured outline needed to cut these shapes accurately. The other image is suitable for inkjet or laser printing so that you can cut the two parts by hand. If you are cutting by hand, the SOLID lines are cut through, the DASHED lines are meant to be scored or folded. Using either one of these you can scale the final product to the size you want. My original project is based on a scale in which the sides of the equilateral triangles are 3 inches long.

I want to add the Silhouette file to this Instructable, but I keep getting an "internal server error" from Instructables.com. Until I can get that to work, please find the file here at my personal G-Drive:

https://drive.google.com/file/d/1ouqU0t1BNrynhmpSoa_ZmzUatO63RKP4/view?usp=sharing

Step 2: Connect the Two Halves at the Joint Point

When you are finished cutting, you will have two identical paper parts. To assemble them correctly, take one of the parts and flip it over so that one part is the mirror image of the other part. When you do this, you make it possible for every edge line which does not have a flap built into it to match an edge which does have a flap built into it.

Connect the two parts as shown in the image above using super glue.

PROTIP: apply the glue to the FLAP, and align the DOTTED LINE to the edge of the other part. Lay down slowly and keep the edge lined on the DOTTED LINE. Super glue binds to paper is a surprisingly-instantaneous way. It will be very easy to have to make two new parts because you misaligned this first joint.

Step 3: Numbering the Sides

If you are adding the foam overlay, just bookmark this step for future use. For those in a hurry, just apply your numbers to the sides according to the diagram in the above image.

PROTIP #1: "6" and "9" are hard to distinguish on dice. Add some sort of baseline indicator to "6" and "9" so there are no controversies when you roll this die. In my final product, I added a "." before and after the digits to show which way is right-side up.

PROTIP #2: For those of you who want to know about the alleged science of making gaming dice, there are several schools of thought.

School 1 says that there is no way to make a paper die correctly balanced so that it is actually rolling in a random way. It really doesn't matter how you lay out the numbers on this project because it's not going to be a perfectly-random number generator anyway. Lay it out however you wish!

School 2 says that if your die is somehow miraculously balanced so that it is equally likely that any side will land on the bottom (therefore: the opposite side will land on top), it still doesn't matter how you layout your die. Just put all 20 numbers on there and enjoy!

School 3 is made up of dicing warlocks, and they believe that their system of numbering the die will render the best results when you account for the fact that no die is perfectly balanced and every die should be somewhat fair and random. The numbering in the diagram above follows a version that logic. The obvious attribute of the system is that all the opposite faces on the die add up to 21. (20 opposite 1; 19 opposite 2; 18 opposite 3; etc.). Some people want there to be a purely-mathematical reason for the layout, and if youa re interesting in that discussion, you can follow a version of it here:

https://www.reddit.com/r/math/comments/1j86p4/d20_...

Step 4: Fold and Glue

The picture above is a PROTOTYPE I built in which I did not follow STEP 2, so half of the open edges do not have a flap joining them. However, you can get the idea quite well from this photo.

1. Prebend all your scored/dotted lines. This helps the die come into shape as you glue the flaps.

2. Glue one flap at a time. If you apply glue to flaps you are not handling, they will stick to things you do not want them to stick to.

3. Be CAREFUL to line up the edges and flaps with high precision. Low precision gluing will create very obvious gaps which you cannot fix except to start over.

4. Leave the last face UNGLUED, and proceed to the next step...

Step 5: Add Filling for Weight

This step is quite easy to overlook, but the reality is that paper dice are more like balloons than solid objects. They need some weight to be useful as an actual gaming tool. I shopped hard to find the best filler which had low weight and high volume because you also do not want this to weigh more than the paper sides will support. In the end I settled on shredded paper, and I filled the shape to the gills before closing it off. It now weights less than 2 oz, and it has enough weight to roll and not too much weight to be more of a weapon than a tool.

Step 6: OPTIONAL: Create Foam Panels for Numbered Sides

If you have already applied numbers to your paper structure, SKIP THIS STEP.

If you are going for the full effect, reprint the template above (twice). When I did this step, I used spray adhesive to make these templates stick to the foam sheets. Then I cut EVERY LINE (dotted and solid) to create 20 identical triangles. It is important to cut these triangles CAREFULLY so that they match each other and also match the faces on the paper polyhedron.

For numbering, I cut out the numbers 1-20 from glittery silver permanent-stick vinyl (you could very easily buy permanent-stick numbers from an office supply store or a craft store). Then I added the numbers to the triangles so I had 20 numbered triangles.

Step 7: OPTIONAL: Glue Triangles to Paper Polyhedron

You can skip this step if you skipped the previous step!

This step adds two things to this project: a little mass and a lot of structural stability. Before you start, make sure you have a numbering pattern in mind for your die (see step 3 if you skipped it and want a better explanation of why this is important).

Pick a face to start with, and the numbered triangle you want to apply to it.

Since we are using quick-set epoxy, take your tube of two parts and squeeze out ONLY AS MUCH AS YOU WILL USE FOR THIS FACE. I had a helper, so we mixed enough glue for 2 faces at a time, and she applied glue while I applied faces. You want to use the glue before it starts to heat up and set because once it starts exotherming it is very difficult to apply evenly.

As you apply the face with the glue, line it up according to the actual sides of the face on the paper polyhedron. If you cut precisely, you should find that the foam fits the face very precisely. Press down gently to make sure that the glue on the back of the foam touches as much paper as possible. Repeat 20 times following the numbering pattern you decided on to make this project as cool as possible.

PROTIP: Wear gloves when you apply glue, and as the gloves get glue on them, throw your gloves away. Keeping your gloves clean will keep your triangles from getting unsavory glue spots on the faces.