How to Make a Giant Decoding Disk

Do your kids like secret codes?

A couple months ago, my son started making paper decoding disks to write secret messages. The idea was inspired by this cool book for boys (affiliate links included in post). Since then, we have been writing messages for each other and even before school ended, we prepped disks for his entire class. We have been having so much fun with code writing, but then maybe I’m just a secret spy at heart.

Where it went from there . . .

After the tree house was finished, we had a medium sized stump sitting there looking all lonely. It was asking for something to be done with it. At first, I thought I would just buy a large wood round to make a table top for when I was bringing a tray of lemonade out to the kids. Practical, right?

And then it hit me like a big wood circle smack on the head. I should build a giant decoding disk. It would serve as a spot for me to set a tray but with the additional feature of decoding ultra secret messages, it would be beyond cool.

If your kids like decoding secret messages, this is a project they will love! I kept it a surprise until it was all done and did our final reveal as the end of a scavenger hunt.

Materials Needed:

Two wood rounds – 18″ and 24″.
Tape – preferably painter’s tape
Pencil
Ruler and Square (I used both, but you could make do with just one.)
Wood Burner Tool
Lag Screw – 3/8″ x 6″
5-7 washers
Stain
Sealer
Drill
Ratchet or Impact Driver with 3/8″ ratchet socket
Hammer
7/8″ furniture glides
Tree stump or table base

I purchased my two wood rounds at Home Depot. Check their site to see if they have them in stock at your local store. I talked to one person who told me they didn’t have them, but then when I asked a different employee and showed him my phone with an “in stock” report, he searched until they were found.

You would be smart (as in I was not . . . ) to determine the center of your circle first. See the video below for instructions. I like to eyeball things and wanted to dive right in. And so I did.

The first thing to be done is marking where the 26 letters of the alphabet should go on the smaller wood round. I created an asterisk of painter’s tape to help me divide the space. Keep in mind that with 26 letters, 13 need to occupy each half. This means that A and N should be directly opposite each other.

Once marked with tape, write the letters in pencil.

Check to see that the size of your letters is consistent. I used my ruler edge for the start of the letter and then adjusted my letters to be just over an inch tall.

Once you are happy with your letter positioning and sizes, pull out the wood burning tool. This takes a little practice, but even after doing quite a bit, some of my letters weren’t exactly pretty. The tool needs to be very hot. Take a break every so often between letters to allow the tip to reheat. Smooth, strong strokes is what you are trying for.

If you have never used this kind of tool before, I would suggest practicing on a piece of scrap wood first. Get the feel for holding and applying pressure as you move on the wood. If you hold too long in one spot, you end up with a divot as the tool burns down in the wood. Practicing first will definitely help.

If needed, go over the letters with the burner a second time.

If you haven’t yet found the center of your wood rounds, this is the time to do so. I used a square as in the video below. You need to determine the center of the circle (and complete the next step) before you write your letters on the larger wood round.

Once you have determined the center of the circle, drill the holes. They will need to fit the 3/8″ lag screw.

There are two ways to determine spacing of your lower round letters. You could repeat the process from the first round or determine the placement based on the upper round. I chose the latter. To space out in this way, line up your wood wounds by putting the lag screw in place.

Write the letters on the lower round in pencil, working through the entire alphabet.

Again, pull out the ruler to ensure consistency. Adjust as necessary. Erase as necessary. I made these letters larger . . . 1 3/4″.

TIP: If you can’t get all your pencil marks off and you are using a light stain, grab a piece of sand paper and sand them off.

Next, separate the two wood circles for convenience and burn the letters on the lower round.

Once both sets of letters are burned, you will need to create code keys as in the photo above.

When you send a code, you have to tell your kids how the code should be deciphered. How will they know where to start the decoding disks so that they can correctly translate your message? Will you tell them to line up the boards where A = K? Or will you use special symbols? I chose symbols.

If your board turns like mine, you may not be able to spin the circles and have the letters all line up every time. I had three positions where the letters lined up nicely with each other. At these spots, you will need to burn code key symbols.

I chose infinity, an asterisk and three dots (“therefore” in math terms) as our symbols. When the kids receive a code from me, I will put one of the symbols at the top of my message. The kids will then know they need to line up the symbols so that they can determine the correct message.

When you are all done burning, stain the decoding disks to the color of your choice.

Seal your disks. I used a water sealing for decks that happened to be 20+ years old and it left certain parts sticky.

So I added a couple coats of acrylic indoor/outdoor spray.

Now it is time to start building. Grab your hardware, tools and head out to your tree stump or table base.

The furniture glides will help your upper decoding disk slide on the lower disk. Think of it as creating a lazy susan and these guys will not only keep the two layers separated, but also help in supporting and turning the upper disk.

Hammer the glides into the board. If you have purchased the same sized materials as I did, there is no need to worry that the sharp ends of the furniture glides will poke through the bottom board.

Drill a pilot hole into the stump. Make sure you drill an appropriate size! We did not make it large enough and snapped the screw. Thankfully, the stump was a little oblong and we drilled a new hole right next to the original spot.

Check and see how many washers you need between the boards so that they don’t exceed the height of the furniture glide.

Now, position the center hole of your lower decoding disk above the stump’s pilot hole. Then, line up the washers over the hole.

Add your top decoding disk and another washer. Then, insert and tighten the lag screw down through the wood and into the stump using either a ratchet or impact driver.

Just for clarification, here is the order of materials from top to bottom:

Lag Screw
One Washer
Smaller Decoding Disk
Furniture Glides and Multiple Washers (to match height).
Larger Decoding Disk
Tree Stump

Here is what it looks like when complete:

I sent the kids through the house and the yard on our scavenger hunt. This was the final clue.

(Arbor Home = Tree House)

Notice my code key for this secret message is the infinity symbol. The kids had to line up the infinity symbol on the upper and lower disk to figure out the meaning of the code.

Here they are running through the woods to discover their surprise.

Writing a code to his sister!

When writing codes, I find it easiest to write the letter of the top disk on the paper to point to and reveal the letter of the lower disk. But make no mistake, writing the code takes concentration and super spy focus. It is easy to get mixed up and write it in reverse.

Have fun, my spies!

What would your kids think if you built this giant decoding disk for them? Would they love it?