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
Gear Generator Program (http://woodgears.ca/gear/)
Vector Drawing Program
Mach3, EMC, or similar (http://www.machsupport.com/) (http://www.linuxcnc.org/)
CNC Router or a contract fabricator – (www.100Kgarages.com)
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
Dust collection system
Step 3: Drawing Programs
There are so many design programs out there (http://crunkish.com/top-ten-cad-software/) (http://www.freecad.com/)http://www.freecad.com/. 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! (http://www.guitar-list.com/download-software/convert-sketchup-skp-files-dxf-or-stl)
I downloaded Gear Generator (http://woodgears.ca/gear/) 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
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. (http://www.rhino3d.com/resources/display.asp?language=en&listing=545)
For those of you who want to learn about g-code there are sites that will show you what it all means. (http://www.cncezpro.com/gcodes.cfm)
Step 5: Selecting the Bit
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
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
----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.) (http://solsylva.com/cnc/vacuum.shtml)http://solsylva.com/cnc/vacuum.shtml
Step 8: Power the Machine and Computer
Step 9: Zero, Zero, Zero
Step 10: The Magic
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
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 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
Step 14: Why We Want to Win
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
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
Thank you for considering this submission