Introduction: CNC Paddle Maze

One day I was at the toy store looking for presents for my children and I came across some small plastic mazes, you know, the type with the little ball that you try to get from the start to the finish without going crazy. Bingo, here was a project for the CNC router we have in our Maker Space.
The design that developed was a circular format with a handle, like the old paddle ball games. Additionally I wanted to store two balls on the game in the hope that they might not get lost as readily.  Old timers disease was making me forget that a job always takes more time and money than expected, along with opportunities (substitute, “problems”), to be had.

Step 1: Your STUFF

Things you need / Materials and equipment list:
Small steelie, ball bearing, BuckyBalls, marble, etc.
Graph paper, pencil, and  good eraser.
Dial Indicator
Vector Drawing Program
CAM generator
Mach3, EMC, or similar   ( (
CNC Router or a contract fabricator – (
Tooling Bits
Portable Drill
X-acto, utility knife, something sharp
Sandpaper or foam blocks
Children for Beta test

Step 2: My STUFF

(Things I need)
Dust collection system
Writing skills
Photography Skills
More tools
Bigger tools
Faster tools

Step 3: Measure and Sketch

Take the spherical object (ball) you have chosen and measure it with a dial indicator. Once this is established you can begin drawing a maze. I like graph paper, pencil and a big eraser. I’ve been known to change my mind (substitute, make mistake). First select a shape you want to work in (circle, square, octagon, etc.).
BIG MATH SECTION:  Ok, you have the diameter of the ball you have chosen, You are about to determine the width of the race (the groove the ball will travel in). Take the diameter of the ball and multiply it by 1.25. Write that down. Do it again by 1.5. Write that down also. This is the width range of the race that I have found to work well.  An example is like this. I am using a BuckeyBall Magnet (you will see later why) that is .200” in diameter. So 1.25 x .200” = .250”, and multiplying .200” x 1.5 = .300”.  So the range of the width of the race should be between .250” and .300”.
I drew the maze within a circle and added a handle to it to make it a one handed game (of course, you must use your non-dominant hand, to make it harder).  I chose 10 races (that is 10 concentric circles), plus the center goal (.75), and a rim around the circle to keep the ball more likely to avoid the floor.  I selected pine, a 1/4” end mill and a width of .200 for the dividers.
Now take out the graph paper, pencil and eraser and get to work. You’ll think this step is soooo… old-fashioned in this day of computers. It may be, (so am I, at least somewhat advanced in years) but having it figured on paper saved me a lot of wasted time.

Step 4: Drawing Programs

There are so many design programs out there ( ( Some are free, some are not. Try the free ones, or the trial downloads, and spend some time assessing their capabilities. Make sure you look at what they can import and export. This will be important in moving your drawing files to the CAM generator (more about that later). The higher end ones, have a steep learning curve and take a while to be comfortable with.  The lower end and free are getting better all the time.  Check out Sketchup (free) with the ruby script that allows output in .stl and .dxf formats. Sweet!  (
I drew two circles from the center, .75” (goal) and .325” (starting circle) then a series of concentric circles .45” apart (.25” bit plus .20” for divider) outward to the rim, then another .5” for the rim itself. Then I drew a handle. Now, I made a bunch of .45” circles and drug them into place as sketched out on the graph paper. After a lot of clipping and joining vectors, I had a drawing.

Step 5: Output to CAM

(CAM - Computer Aided Manufacturing)
Some drawing (CAD) programs have no way to get g-code from them. G-code is a language defining where the router must go to perform the task you have in mind and is generated by the CAM. Some CADs have CAM with them but they tend to be the pay for types.  For those of you who are using a CAD program that does not have this function, you’re going to have to find a separate one to do this. Here is some links. (

Step 6: Selecting the Bit

On our homemade CNC machine, is a Porter Cable Trim Router. It will accept ¼” shank bits.  As I had selected ¾” pine, I chose a ¼”shank 1/4” end mill. This means it is strong (thicker shank), and will cut 1/4” wide with a square bottom.
Our router only goes one speed in rotation and maxes out at 25 linear inches per minute, so the only control we have is how deep it cuts per pass, and the inches per minute speed it travels thru the material. I planned for each pass at .25”.  Before any machinery is turned on, install the bit into the router you have. Be VERY careful, they are quite sharp. I wouldn’t know that, but, there are a wide range of band aids and compresses readily available in our shop, just in case.

Step 7: Load the Material

Most of the time when running a new project, I will select blue or grey insulation board. This allows me to see how many things I screwed up in the drawings and parameter commands. It also creates a prototype that can be checked to see if it really does work.  Lastly, if the project is cut completely from the waste material, I have a template that will prove useful. I went ahead and loaded the pine, in the hope all would be well. Sometimes you're lucky, sometimes you're not.
Make sure that the piece you load on the machine is bigger than the project. Seems obvious, doesn’t it. Also that it is oriented correctly in the X and Y plane. I never make that mistake.
Stabilize the foam (or the pine). Many treacherous opportunities lie here. Cut the foam/pine larger than the project.  You want extra room for clamping down the outer edges with screws, cam locking devices, or even double-sided tape.  In this case I clamped it down with sticks and screws. Regardless of the method, one wouldn’t want the highly rotating router bit or the router itself crashing into something hard and unyielding. Some very interesting results WILL occur and you really don’t want that experience. The least is you may lose some steps in the g-code and get the remainder of the cut all cockety-wampuss,  the worst is flying bits of high speed steel flying around. Which brings us to the all-time favorite subject of OSHA,   da-da… SAFETY.

Step 8: SAFETY

Here we go, ignore this at your own peril. Ok, the condensed version:
---Ears - CNC machines are loud. I like to put on noise cancelling earphones with my favorite music playing in the background. Not         too loud as you want to lightly hear the machine as it runs, giving you a heads-up to any problems.
---Eyes and face – Flying objects do sometimes come from the machine, best to protect them. I use a face shield.
---Breathing – All materials have some dust created during the cut. Use at least a filter mask for non-toxic woods and cardboard something better for MDF and plastics.
---(If at all possible make or buy a dust collection system to keep the fumes and dust to a minimum. That’s the next project for us after this contest. Wish I had done it earlier.)  (

Step 9: Power the Machine and Computer

At last the fun begins. Power the machine and computer and open up Mach3 or EMC. These are the interfaces that actually translate the g-code into movement by the router. EMC is the open-source Linux version, Mach3 works with windows. Next load the g-code using a flash drive, wireless or whatever you move files with from your cozy office to the cold and manly shop. Look at the screen and click the Reset button. Now you can move the non-running router around to position the 3D coordinates (X. Y and Z) of the bit by using the number pad on the keyboard.

Step 10: Zero, Zero, Zero

You really want to fire that thing up. You have been at it for a while. You are impatient (well that, at least, describes me at times). But we have to get off on the right foot, or inch, or thousandths of an inch. X, Y and Z must be zeroed. Most of the time, this point will be the top-lower-left corner of the drawing.  Be slow and careful to NOT run the bit into the material or hold-down clamps. The tooling bits, I’ve found, do break, and are pricey. Once over the zero, lower the bit ever so gently down to just above the top of the piece. Then I place a feeler gauge below the bit and, extremely slowly, move it down to just touch the gauge. Using .002 gets the bit located in space just half-a-hair above the material. You do remember NOT to have the router on during this step. Right?

Step 11: The Magic

It’s finally time to turn the router on and start the sequence of cutting from Mach3.  Just like your mother used to say “don’t forget your mittens”, remember the safety stuff.  Turn the router on first.  Then click the green button on the screen labeled Cycle Start. You’re off and cutting. Yeah!  If it takes off in some bizarre direction, be ready to shut it down by clicking the STOP button. Remember the adage that computers, (along with dangerous machines attached to them) only do what you tell them to do, not what you want them to do. If all is going well, just watch and enjoy the moment. To me, this is amazing stuff, I used to hand cut all of these projects. It’s a wonderful world!
When the cycle ends, and the router comes back to zero, turn it off. Then remove all the clamps, screws, staples, or what-have-you that is holding the material firmly. Pick up the piece and be amazed.  Remove the waste sections, and vacuum or blow off the dust so the machine is ready for the next fabulous project.

Step 12: Examine

Now is the time to really look at your product.  Test it, see how the ball rolls, check the turns, play a while. You deserve it
If you think it needs improving, return to Step 4, and go for Plan-B, or Plan-C, etc.  Most of the time, it takes several tests and iterations to get it right.

Step 13: Finishing

I’ll fly through this part, as I’m sure most of you will have some experience at this.
I used another Porter Cable Trim Router to round over the top and bottom of the paddle, prior to hand sanding.
Using foam sanding pads, I smoothed all the surfaces, especially the races and dividers.
Clean the paddle with air or a brush.
Apply stain carefully to the wood, and wipe excess off with a rag, especially the races.
Allow to dry.
Finish with spray polyurethane.  Do this outside and wear a mask anyway.
Allow to dry completely.
Glue in the small washers in the storage holes and stick Bucky Balls to them

Step 14: The Real Test

Give this game to some children. See what they do with it. They will surprise you with a host of variations on how to play, make up new rules, and find uses for the paddle that were not in your mind when you had this brilliant idea. After observing them for a while, breaking up squabbles, and making them share; think about any improvements or changes in design you may want to implement. Maybe redesign the maze to be harder or easier. Maybe beef it up a bit, allowing for the extreme conditions it will endure. Who knows, keep those mental juices flowing and see what develops. All this work is, after all, really and truly play.

Thank you for reading this far. Hope it was instructive. Please post any questions, comments, suggestions or ideas, and I’ll get back as soon as I can.

Step 15: Why We Want to Win

Last summer Mike and I began getting together at least once a week or more, for what we called guy time. We would work on some idea, hack, project, or repair of some item with what we had in the shop. This resulted in some clever solutions using rather odd materials. The interplay between us was so fun we began to invite others to our “club”.  Thus a Maker Space has taken over my shop. I love it. About this time Mike introduced me to and I was hooked. He also brought over his homemade CNC Router.  We got it up and running and have been creating a number of interesting projects that are being submitted for this contest.

Our club of makers would continue to explore the vast world of CNC routing. We have in mind a large backlog of ideas that would be furthered by winning the PRS Standard 96-48-6 ShopBot .  Our homemade CNC can cut 31” x 21” and cuts at a maximum of 25”/ min.  The 4’ x 8’ table and 300”/min will vastly improve our ability to produce prototypes, develop and improve designs, create larger projects and test out 2.5D, then move to full 3D sculpting.
Here is a small selection of my personal list of projects:
                    Mazes for more than one player
                    Multi-level mazes
                    Giant mazes on a half sphere to be played by young children
                    Interchangeable mazes of increasing difficulty
                    Picture frame mazes
                    Spirographs – small 8.5 x 11
                    Giant Spirographs using chalk for outside
                    Wing Ribs for Experimental Aircraft
                    Patterns for Cabinet doors
                    Wood Blocks for printing from ancient lithographs
                    Bas reliefs
                    Negatives for molds
                    Negative busts
                    Full Busts
                    Art prototypes

Thank you for considering this submission
Rick Shore

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