Introduction: Rainbow Sudoku Set

About: Research is what I'm doing when I don't know what I'm doing.

I've always wanted to make a colourful Sudoku game and the Instructables Rainbow contest was the perfect excuse to get the paints out and fire up the workshop!

Sudoku is normally played with the numbers 1-9, but you can have more fun by replacing numbers with pretty colours! Also, bringing the game off the page and into 3D space makes for more collaborative puzzle solving! Try leaving an unsolved puzzle out for people and see how no one can resist having a go!

The game of Sudoku has been somewhat of an obsession for many mathematicians, although it has taken a number of variations and names throughout history. There are approximately 6.67E+21 (that's 667 with 19 zeros after!) unique solutions to the Sudoku puzzle!! It has also been determined that the minimum number of clues possible for a proper Sudoku is 17, with over 49,000 of these solutions found!

You can play the Rainbowku (I know, terrible portmanteau) by obtaining any Sudoku starting puzzle (widely available online) and assigning colours to the numbers. As long as you keep consistent colour/number mapping the game can be played. This is how I've been playing so far, but I now have an ambition to code up my own Sudoku puzzle generator that will output in colours. I can then just print off my puzzles and not have to worry about the colour/number mapping system.

This set was made with a single pine plank and some wooden balls purchased from a seller on ebay. With some basic tools and a selection of paints, you can make your own too :)

Step 1: Materials

Wood -

The board is made from a single plank of pine, measuring 900 mm in length, 90 mm in width, and 15 mm in thickness.

I also had a scrap of plywood to make a holder for the wooden balls while I painted them.

The wooden balls are 12 mm in diameter and are from a supplier on ebay. I considered making my own wooden balls, but making a minimum of 81 balls seemed tedious. I then discovered I could buy blank balls for very little cost; the listing can be found here.

Paint -

The paint I used was Acrylic paint. It paints well onto wood and gives a satisfactory finish. You will need 9 different and easily distinguishable colours.

Tools -

You'll need a pencil and straight edge, as well as a saw to cut the plank into three equal sections.

You'll need some clamps and some wood glue.

I used a CNC router with a ball nose bit to make the board, but it really is a simple design and can be made by other means. I did some experimenting with the ball nose bit chucked in a hand-held drill and got some satisfying results.

Step 2: Make the Board Blank

I started by cutting the pine plank into three equal lengths and gluing them together. Be sure to get an even covering of glue and good contact between sections. Good contact is the key to making a super strong join; if done properly, the join is often stronger than the wood!

Be sure to wipe away any squeeze out and let the glue dry overnight. Once glued, give it a good sanding and you'll have a nice pine board that will soon become your Sudoku board. I also drilled 10 holes in a scrap piece of wood to make a holder for the wooden balls to dry.

Step 3: Painting!

I painted 10 wooden balls of each colour; you only need 9 but I thought I'd do extra in case I lose one.

I found the easiest way to paint the balls was to grip them in some large tweezers and paint all a can, then when I set it down to dry, I hit the bits the tweezers were blocking. By the time I had painted ball number 10, the first ball was ready for a second coating. I found three coats to be the optimum number of coatings, and yes, it was time consuming. I would set several hours aside to do this step, or better yet, buy more brushes and enlist some friends and family :)

A more efficient way to paint the balls would be to use spray paint, but this can be expensive to buy 9 cans of paint. If you own an air-brush, this would also be an ideal method!

Step 4: Making the Board

As mentioned earlier, I used a CNC router to make my board, but there are other ways. The CNC was fitted with a ball nose bit (12 mm diameter) to make the divots where the balls will sit. I used a 1.5 mm endmill to make some dividing marks to show the 3x3 sub-regions, and a 3 mm endmill to cut the board away from the stock.

The SVG file here contains the vectors needed to generate your own machine code, however, if you don't have access to a CNC machine there are other ways to make this relatively simple design.

The SVG file is a 1:1 scale drawing and can be printed off and attached to the board blank to be used as a guide. I did an experiment where I used the ball nosed bit in a hand-held drill and was able to get good results making wells for the wooden balls. You could also use a drill press, which would give you good depth control too. Using the ball nosed bit in a standard router, together with some well placed stops, can give you the perimeter groove.

I finished the board up with lots of sanding and finally, a coating of linseed oil.

Step 5: Conclusion

I would have liked to try this project using non-cnc techniques, however, I was pressed for time on this one :(

To play a game, I obtain a starting puzzle from an online generator such as this one here and assign colours to numbers. Eventually I would like to code my own generator which just uses colours and would allow me to print out my starting puzzles.

Some improvement that could be made to this game would be the inclusion of draw to store the balls when not in use. Another improvement would be to somehow mark a number of the coloured balls to show which balls are the "Clue" balls that should not be moved. Perhaps painting a black dot on a number of extra balls would be sufficient.

I hope you enjoyed reading this Instructable as much as I did making it, and good luck making your own RAINBOWKU :)

Colors of the Rainbow Contest

Eighth Prize in the
Colors of the Rainbow Contest