Introduction: CNC Spirograph

Some months ago I remembered a drawing tool I played with as a child, the Spirograph.  Searching local stores only resulted in a small, poor substitute in plastic, of the ones I remember. Thus the inspiration and the idea for this project grew. I have a background in fabricating Museum, Zoo and Nature Center exhibits. For 25 years I was asked to build the most amazing things. This project would be no problem.
The design in mind included;  #1) large enough to fill an 8.5 x 11 piece of paper,  #2) the holes would fit fine-tipped Sharpies,  #3) the “look” would be industrial gear-like,  #4) made of wood, not plastic,  #5) be durable considering children would use it.

Step 1: Your STUFF

Things you need / Materials and equipment list:
Gear Generator Program      (
Vector Drawing Program
CAM generator
Mach3, EMC, or similar   ( (
CNC Router or a contract fabricator – (
Tooling Bits
Portable Drill
Staple Gun or screws
X-Acto, utility knife, something sharp
Baltic birch plywood – ¼” 5 ply or similar
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: Drawing Programs

(CAD – Computer Aided Design)
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 downloaded Gear Generator ( for $26 to make this real easy. It draws gears with any number of teeth, inside or out. You can add spokes in any number, and it outputs in .dxf, a useful format. It is also quite fun and very easy to play with.
After generating the ring and gears of various sizes, I saved the files and imported them into my CAD program. I needed to make holes for the fine-tip Sharpies to be placed. After measuring the diameter of the tip of the Sharpie at .15”, I began to place the holes on the spokes at various distances from the center point of each gear. It became obvious that to beef up the narrow wood next to the holes, I would need to widen that part of the spoke. I created a series of ½” circles and placed them concentrically over each Sharpie hole to beef the up wood. Next, I clipped out the extraneous vectors and cleaned up all the images. Thus I had a vector drawing of all the parts on the minimum sheet size. I then cut the 5’ x 5’ Baltic birch plywood into the size needed, 16” x 21”.

Step 4: 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 CAD's 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. (

For those of you who want to learn about g-code there are sites that will show you what it all means. (

Step 5: Selecting the Bit

On our homemade CNC machine, is a Porter Cable Trim Router. It will accept ¼” shank bits, and with collets, will size down to 5/32” and 1/8” shank tooling.  As I had selected Baltic birch plywood, I chose a ¼”shank 1/8” end mill. This means it is strong (thicker shank), and will cut 1/8” 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.  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 6: Load the Material

Most of the time for a test run, I will select blue or grey insulation board. This time I took a scrap piece of ¼’ ply to do the test. This allows me to see how many things I screwed up in the CAM and CAD. 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.
Make sure that the piece you load on the machine is bigger than the project. Additionally I place a sheet of cardboard under the material to protect the bed of the machine. Seems obvious, doesn’t it?  Also, that it is oriented correctly in the X and Y plane.  I never make that mistake.
Stabilize the plywood. Many treacherous opportunities lie here. Cut the plywood 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 used wood strips and screws for the first run, and a staple gun and ¾” staples around the outer edges for the second run. 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, and 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 7: 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 8: 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. 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 9: 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 10: 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 11: Examine

Now is the time to really look at your product.  Test it, measure it, look it over closely. Get a sharpie and see how well it works.
If you think it needs improving, return to Step 3, and go for Plan-B, or Plan-C.  I got real lucky on this one.  Most of the time, it takes several iterations and tests to get it right.

Step 12: Finishing

I’ll fly through this part, as I’m sure most of you will have some experience at this.
I used an X-Acto to clean up feathers left from the cut
Using foam-sanding pads, I smoothed all the surfaces, especially the teeth
I cleaned the gears with air and a brush.
I didn’t feel that stain would improve the look.
Finished with spray polyurethane.  Do this outside and wear a mask anyway.
Allow to dry completely.

Step 13: The Real Test

Give this game to some children.  Get some paper and a host of colored Sharpies and let them go at it. See what they do with it.  After observing them for a while, breaking up squabbles, and making them share; think about any improvements or changes in the design you may want to implement. Maybe redesign the teeth for a better fit. Maybe change the ring shape in some way. Keep those mental juices flowing and see what develops. All this work is, after all, really and truly, play.

Step 14: 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:
                Giant Spirographs using chalk for outside
                Wing Ribs for Experimental Aircraft
                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
                Patterns for Cabinet doors
                Wood Blocks for printing from ancient lithographs
                Negatives for molds
                Negative busts
                Full Busts
                Art prototypes

Thank you for considering this submission
Rick Shore

ShopBot Challenge

Finalist in the
ShopBot Challenge

Make It Real Challenge

Participated in the
Make It Real Challenge