Introduction: CNC Solitaire Game

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About: San Francisco entrepreneur, working to improve access to healthy locally grown food.

I saw this beautiful wooden solitaire game on a friend's coffee table, and after an hour playing, decided to make one for myself. The game is fun and challenging, the board looks great on my coffee table, and most importantly, it's a great beginner's project if you're just learning CAD/CAM/CNC (as I was!).

For this project, you'll need access to a CNC machine and some basic knowledge of how to use it. I made mine on a ShopBot at TechShop which has locations in AZ, CA, MI, MO, PA, TX, and DC, but most large maker spaces will have a machine that works.

You'll also need access to CAD/CAM software. SketchUp is a nice free option, or you can get a free trial of Fusion 360 if you want something a bit more powerful. For this project, Fusion has the advantage of better handling of curved surfaces and built-in CAM tools, but either will work. These instructions assume you're using Fusion and know your way around the software, but the process is very similar in SketchUp. You can also download my design and start from that.

Step 1: Choose Your Marbles

Before you can start designing, you'll need to pick the marbles you want to use, since the diameter of the marble will dictate the size of the board. You'll need 36 marbles that are all the same size.

I used a bag of marbles from the hardware store, which turned out to be 5/8" in diameter.

Step 2: Design the Board

In your CAD software, start by building the basic cylinder for the board with a track around the edge.

Create a new sketch on either vertical plane, and draw a rectangle starting at the origin -- this will become the main cylinder. The height should be the desired height of the final board, and the width should be your desired radius. For my 5/8" marbles, I used a .75" height and 4" width.

Then cut out a semi-circle from the top right to form your track; it should be the same diameter as your marble.

Finish your sketch, and use the Revolve tool to revolve the sketched profile around the vertical axis to form your board.

Step 3: Add Pockets

Now add the pockets where the marbles will sit. I wanted them to sit slightly higher than halfway down to make them easier to pick up. To do this, create an Offset Plane slightly above the top surface of your board. Then create a sphere on that plane at the origin, using the diameter of your marble and a "Cut" operation. This will cut your first pocket right in the middle of the board.

Then use the rectangular pattern tool to create the rest of your pockets. Create 7 pockets in each direction, centered on the middle of the board. Use the checkboxes to suppress the outer 2 on the first and last row and outer 1 on the second and second-to-last row, so that you end up with one row of 3, one of 5, three of 7, another of 5, and another of 3.

Step 4: Make Your Toolpaths

With your design done, you're ready to convert it into instructions for your CNC. This step depends a lot on what software you're using and what tools you have available, so if you're new to CNC, you'll want to ask for advice at your shop.

If you're using SketchUp, you'll need to export your design to a standard format like STL and then use external CAM software. I used Cut3D for this and got good results (though slightly jagged pockets since Cut3D doesn't support circular paths). Most shops that have a CNC machine will provide CAM software that works with their machine.

if you're using Fusion 360, you can use their built-in CAM tools. If you happen to have a ball end mill that matches the diameter of your marble, you may be able to just do a single 2D slot for the outside track and drill holes for the pockets -- but more likely, you'll need to use more elaborate 3D tool paths. I used 3D Adaptive Clearing with a bigger end mill to rough out the shape, and then a series of Spirals to finish the pockets and outer track.

Once you're happy with your toolpaths, use the Post Process function to export gcode for your CNC, and you're ready to mill!

Step 5: Mill Your Board

Now comes the fun part - actually milling your board! The milling process varies widely by machine, so follow the appropriate steps for your CNC.

Obvious disclaimer: CNCs are very powerful machines with sharp tools running at high speeds, and can be extremely dangerous. Most maker spaces have classes in CNC operation and safety, so make sure you're fully trained on your machine and understand how to operate it safely before you start.

Step 6: Sand and Stain

Sand down any rough surfaces, then stain your board to whatever finish you like.

Step 7: Play!

Now for the hard part: playing the game!

The rules are simple. Start with marbles in every pocket except the center one. Marbles can hop each other like in checkers: a marble can hop over any adjacent marble vertically or horizontally (but not diagonally), and the jumped marble is removed from the board and placed in the outer track. The game is over when no more moves can be made, and the goal is to get as many marbles off the board as possible.

I've gotten down to 2 marbles (once), but never been able to get rid of that last marble. How far can you get??