Introduction: Cryptic Calendar

About: I am engineer & hobbyist. “If you want to build a ship, don't start looking for wood, cutting boards or distributing the work. It first evokes in men and women the longing for the free and wide sea." Antoine d…

Lots of people like gadgets. I am not the exception to the rule.

There is a YouTube channel called “Grand Illusions” where his author Tim (Timothy Quiller Rowett) presents curiosities, toys, etc.

At this site I saw a cryptic calendar for the first time.

As I liked it, I tried to find it to buy it on the web. Since I couldn't find it, I decided to build it on my own.

In this tutorial he explains how to do it very easily.

Let's start !

PS: my special consideration to all the people who are suffering from COVID-19.

We all hope that scientists can find a vaccine !!

=== EDITED 4-NOV-2020 ===

-in step 2, files are again available in the onedrive link.

=== EDITED 12-DIC-2021 ===

-in step 8, I add 3 image with secret files measurements.

=== EDITED 28-AUG-2022 ===

-in step 2, I add Adobe Ilustrator file (*.ai)



- Wooden Plywood 12 mm.

- Black PTEG or PLA filament.

- Metal Keyhole hanger (1)

- Epoxy pegament.

- Black Acrylic Paint.

- Clear/Transparent paint spray.


- A table saw or similar.

- CNC.

- Milling bit, double flutes spiral carbide flat nose end mill 1mm cutting diamater and 1/8 shank diameter carbide.

- Straight end mill milling cutter flutes (tungsten Steel) 1/8 ”cutting diameter and 1/8 shank diameter.

- Printer 3d.

- Sandpaper (fine, medium and coarse grain)

- Electric rectangular orbital sander.

- Electric blower or compressor.

- Vacuum cleaner electric.


According to the Cambridge dictionary cryptography is “the practice of creating and understanding codes that keep information secret”.

If you are interested in the subject, there is a lot of bibliography on the subject on the web.

Here you could see a lot:

In this project we will build a wooden table that contains signs (triangles, squares, rectangles, etc.) that are indecipherable at first glance.

But, when we place a plastic template (the secret key) on the table and slide it from top to bottom, each of the 31 days of a calendar month magically appears individually.

See the included schematics to understand how encryption and decryption works.

Step 2: DESIGN


The first thing I did was look for the type of font to achieve the desired effect.

The appropriate font is "Porker" designed by Robert Schenk. Note that there are some others fonts with which a similar effect.

In the attached photo you can see what a normal number, an encrypted number and the decryption process are like with the help of a template (key secret)

Adobe Ilustrator

With Adobe Illustrator (AI) I generated a drawing with the 31 calendar numbers in POSITIVE, that is, black color and white background. I made two columns: on the left the numbers 1 to 16 and on the right the numbers 17 to 31.

(file attached).

Moho(ex anime studio)

Then I imported the AI file from the MOHO program, which has a lot of versatility to work with vector drawing and animations.

I completed each of the boxes for each number, and I turned the numbers to NEGATIVE, that is, a white font and a black background.

Then I erased all the white background lines, leaving only the black ones. In this way the table of numbers from 1 to 31 was “encrypted”.

I exported this image to JPEG file (see note 2)

With software moho I made an animation to test the numbers and the key secret (please see video).

Aspire Vectric

I exported this file as JPEG and imported it with Aspire software to be able to create a GCODE to work in a CNC machine.

I think it would also be possible to make the drawings with a laser.

For the shapes (squares, triangles, etc.) I used milling bit, double flutes spiral carbide flat nose end mill 1mm cutting diameter and (1/8 shank diameter carbide)

For cut the outer edge, I used a bit straight end mill milling cutter flutes (tungsten Steel) 1/8 ”cutting diameter (1/8 shank diameter).

The feed rate that I applied to carving / cut plywood was 250 mm/min.

To hang the calendar on the wall I looked for a metal keyhole hanger.

In the back face of the calendar I made a milling of the wood to install it.

Of course you can use different types of keyhole hanger, depending on what you can find.


(1) you can download my Aspire, Gcode files and DXF, but take special care to adjust it to your CNC (heights, etc.) and your own bits. Also if you decide to use another wood, you will have to change the parameters.!AoZa4oXuD3mOgokIRXiefbm-g0-niw?e=QhuGs4

(2) if you haven´t Aspire Vectric or you use another software you can use the template in JPEG or the DXF file included in the link above to generate the GCODE in another way.

Step 3: SUMMARY OF ALL TASK (See the Video)

To build the Cryptic Calendar, once you have the necessary materials and tools, the tasks are as follows (they will be explained then step by step later).


  • Cut de base wood (340mm x 140mm x 12mm)
  • Fix the wood in the CNC and leveling the base plane CNC.
  • Carving the figures.
  • Aspire the dust.
  • Cut the edges.
  • Aspire the dust.
  • Remove the Wood from CNC.
  • Sand the Wood.
  • Put the wood on the back side, to carving the space to metal keyhole hanger.
  • Aspire the dust.
  • Sand the Wood.


  • Initial sanding
  • Painting the figures (triangles and rectangles) with acrylic paint.
  • Sanding soft/hard to remove excess paint.
  • Use a blower or compressor to remove the dust.
  • Final cleaning and retouch
  • Use vacuum cleaner to clean up any particles or dust.
  • Final cleaning with a dry cloth.


  • Print the “key secret” piece, in black PTEG PAINT FIGURES


  • Paint the surface (front, back and sides) with clear / transparent aerosol paint.


  • On the back of the Cryptic Calendar put the keyhole hanger in the carving position.
  • Install the “Secret key” (printed 3d piece) into the Cryptic Calendar.
  • Choose a wall in your house to install it.
  • Enjoy.

Step 4: CUT WOOD

The final dimensions of the calendar are H= 330 mm x W= 80mm x T=12 mm

For the CNC working process it's necessary to cut a larger dimension: 340 mm height by 140 mm wide.

I've used 12mm Plywood in this project, but another type of wood could also be used.

To cut the wood I used a table saw.

Step 5: CNC

For this process, I used the excellent DREMEL CNC designed by NIKODEM BARTNIK (with 500w chinesse spindle upgrade).

The CNC's work space can may seem limited, but for the hobbyist, and those who have never worked with CNC in general, I really recommend it! (See photos 1 and 2)

Discard this comment if you have another commercial or larger CNC ;)

Preparations before using the CNC

First The first thing I do is make holes in the corners of the wood to work with the CNC to fix it with self-drilling screws. To prevent the screws from sticking out above the Z = 0 level, I make a countersink with a tool for this purpose.(See photo 3 and 4)


Before working with the CNC, with the wood placed in it, I recommend leveling the space of work (Z). This is because we have carving 0.4 mm, which is a very small dimension.

I do it with a small piece of paper, similar to leveling in 3d printers. See photo 5. Photo 6 wooden ready to run CNC.

Carving figures (front)

To carve the figures (triangles and squares) I used milling bit, double flutes spiral carbide flat nose end mill 1mm cutting diamater and 1/8 shank diameter carbide. (See photo 7).

In photo 9 you can see the the finished carving work done by the CNC.

Cut edge (front) and carving space for metal keyhole hanger (back)

To cut the outline of the calendar to its final size I used a bit straight end mill milling cutter flutes (tungsten Steel) 1/8 ”cutting diameter and 1/8 shank diameter. (See photo 8)

In photo 10 you can see the the finished cutting edge work done by the CNC (side front)

On the back side of the calendar I made a carving using the same bit above.

In photo 11 you can see the the finished carving done work for metal keyhole hanger by the CNC (side front)


Initial sanding

Use a regular sandpaper to remove any wood debris as shown in the figure (photo2)

Do this work with the side edges of the wood and on its back.

This previous work is very important, please do the work patiently to get a good result in the following stages.

Painting the figures (triangles and rectangles)

With the help of a small brush and acrylic paint, paint each of the spawned figures from the wood.

Make sure that the painting reaches both the bottom and the sides of each figure.

To do this, distribute paint generously inside the figure and around it as seen in the figures.

Let stand until completely dry. Once it is dry, check that there are no unpainted parts.

With the same brush and paint, make the touch-ups so that 100% is well painted.

Again let stand until completely dry.

NOTE: you can use a heat gun to speed up the drying of the paint.

Final sanding

Now it's Time to remove excess paint.

For this I used:

  • Sponge coarse sandpaper
  • An electric rectangular orbital sander.
  • Coarse sandpaper glued to a small piece of wood.

For this task, the use of safety glasses and gloves is recommended.

First apply sponge sandpaper firmly and evenly across the entire surface.

Then with the rectangular orbital sander I remove 100% of the paint. Do it firmly and evenly across the entire surface. The small piece of wood with sandpaper attached will serve for the final details.

You will notice that the wood dust will accumulate in the carved figures.

The sanding is ready when there is no more excess paint.

Final cleaning and retouch

Now use a blower or compressor to remove the dust.

You will see magically that the paint stays and the job is perfectly done.

With the help of a pointed metal element (such as a needle or similar) remove the dust that may stick to the corners in some figures (see photo 3 and 4)

You can also use a vacuum cleaner to clean up any particles or dust (see photo 7)

Finally, use a clean and dry cloth as a final cleaning.

If you prefer, you can dampen the cloth very slightly and go over all surfaces.


I chose a matte clear / transparent spray paint finish (not varnish).

It is applied following the manufacturer's recommendations, spraying from a distance, avoiding excess paint (drops or similar).

His paint should be applied on the front, back and sides.

The drying of this type of paint on plywood is very fast.


The design of the part was made with AUTODESK FUSION360.

Use a 3d printer to create the part. I have a Creality Ender 3 Pro.

I suggest printing face down as seen in photo 3 (Cura software).

In my case I used black PTEG filament, but you can also use PLA.

I include the file to print.

** EDIT 8-DIC-2021**
I added 3 additional images with dimensions of the secret piece, to check the measurements with your print.


On the back of the Cryptic Calendar put the keyhole hanger in the carving position and applied epoxy cement (I did that) or if you prefer self drilling screws.

Choose a wall in your house to install it.

In my case I made a hole in the wall and installed a fisher wall plug S5 (choose the right model for your type of wall). Height from the floor approximately 1.65 / 1.75 m.

Then I put in a 2.5mm self drilling screw.

Now only remains to hang the Cryptic Calendar on the wall and enjoy the work done.

How to use:

To mark the days of the month from 1 to 15, the 3d plastic piece (Secret Key) must be placed with its square holes on the left side. From number 16 to number 31 the piece must be rotated 180 degrees so that the square holes are on the right side.

Step 10: Final Words

That's all for this project! I hope you enjoyed this instructable.

If you have any question ask them in the comments below!

I would also love to hear what you think about the project.

Happy making!


PS1: if you like the project, please vote for this!

PS2/Credits: "The End" photo Designed by Freepik

CNC Contest 2020

First Prize in the
CNC Contest 2020