Wooden Gear Trains

I've been interested in gear transmission for a while, and decided to play around with the idea using laser cut wood. My original inspiration came from this project on thingiverse, which I adapted into what you see in the second gif above (and fifth + sixth images above). I found the spinning gears really calming to watch, and made a few for friends to keep them entertained at the hospital or when studying for exams.

Since they were quck to design and easy to personalize, I ended up building my own gear trains and cutting out a few as early holiday gifts. My friends really liked the pleasing "clicking" sounds as the gears mesh with each each other so I decided to explore with more designs and share this tale: in which I make great toys to fiddle with.

Step 1: Materials

Basic materials needed for creating the gear trains:

• plywood (I used eighth inch plywood -- I think it was a good thickness, considering that quarter inch would be bulky and sixteenth would be too thin.)
• (optional) acrylic makes nice gear trains too if you happen to have any!
• laser cutter (I used a Universal laser cutter at my school)
• nuts and bolts (I used half-inch long 8-32s so my files are designed for that, but you can adjust the sizing for your hardware. I go through the tolerancing for the holes in Step 3)
• superglue to keep the nuts fastened to the bolts

Optional for if you want to design your own gear trains:

• graphics software (I always use Adobe Illustrator as my weapon of choice, but Corel Draw, Inkscape, etc. would do the same job)
• gear generator (You can use free softwares like this or google "gear generator" for more, plus Inkscape has a gear generator extension, but I used Solidworks to show 3D images of it and really plan out where the gears would go.)

More optional materials to consider:

• acrylic makes nice gear trains too if you happen to have any!
• wood stains for color (or see Step 13 for using food coloring and rubbing alcohol, or even sharpies)
• sandpaper to get rid of scorch marks
• washers to reduce friction between all the wood rubbing together (nylon or metal...)

Step 2: Overview [read Me!]

In this 'ible I included the steps for how I designed the gear trains in steps 4 to 11, but you can go straight to the files for cutting designs that I've already created if you wish. Also, my instructions use Solidworks to provide more of a visual guide, but everything can be done in regular graphics softwares, albeit with different commands!

The file for gear train 0 (adapted from thingiverse inspiration) is attached to this step: see here for instructions. Gear train 1, 2, and 3 are in steps 14, 15, and 16,respectively. Before that, step 13 provides tips on wood staining and designing with colors in mind. For my gear trains, you will need to "break them in" before they work well, due to the minimalistic design and lack of peripheral support to keep the gears perfectly positioned. But once broken in, they work really well!

Future steps and suggestions are in the last step. Enjoy!

Step 3: Hole Tolerance

The hole sizes for the bolts and nuts were decided based on a standard tap and drill tolerancing chart from little machine shop ( pdf attached to this step for convenience). In the Clearance Drill column, you can see the diameter of the hole needed for close fit and free fit (close is to just clear the threads of your bolt, whereas free gives you more wiggle room). At first I went with free fit thinking that the wiggle room would be beneficial, but turns out that it allowed my gears to move too much and improperly mesh. Thus, I went with close fit in the end.

Since I used 8-32 nuts and bolts (8 for screw size, 32 for threads per inch), I went down to "screw size" = 8 and over to the close fit column to get that my holes should be about 0.1695 inches in diameter. Change the holes in your files to fit whatever you have on hand though before you cut out your gears.

Step 4: Part 1: Sketching a Guide

Any good project starts with a sketch to provide vision for how your project will turn out. For these gear trains, you'll need to create sketches consisting of tangent circles to simulate how the gears will mesh. These tangent circles are your pitch diameters -- see step 6 for more details.

Take load distribution into account -- if you have many gears in swirling chains, balancing your load is important so use branches when possible. I explain a bit of this in step 16 with gear train 3, later, but see this video for a nice example.

In terms of design, consider having multiple layers of gears. The more gears you have, the more problems you'll encounter though (the tolerances lead to more wiggle room, and if one gear chips at a tooth that could throw everything off). But multiple layers (as in gear train 3) allows you to play with different gear dimensions so you can have different diametric pitches (see step 6 for gear vocab) in different chains (I didn't do this, actually, but that's what multiple layers of gears would be used for).

Step-by-step instructions on how I created a simple sketch (for gear toy 1) are in notes in the Solidworks pictures above, but Solidworks isn't necessary, as any graphics software will do. Just start with a rough sketch before transferring it into a vector file. You don't necessarily need it for planning, but you do need it to design where your bolts will go.

Even though this is just the bare-bones, where-do-the-gears go sketch, keep in mind that you also need support structures to keep the gears in place in the train (think of the cross in gear train 1, the front circular shape in gear train 2, and the background circle in gear train 3). See step 11 for how I created them, but you should have an idea of how the gears are connected. The easiest way is just to bolt the gears down to a plane of wood (as done in gear train 3) but crosses and such like in gear trains 1 and 2 look nice too.

Step 5: Part 2: Setting Up Axes for Proper Mating

This is only for people following along in Solidworks: in order to center your gears with your circles, you need a reference axis for mating. Follow the step-by-step instructions in the notes of the above pictures on how to do this.

Step 6: Part 3: Generating Gears

Gears need specific geometries in order to mesh properly, and there are entire courses you can take on their design and equations. I won't bog you down with that, so here's a quick guide to gear theory.

There's three main vocab words to know: pitch diameter (diameter of the imaginary co-axial cylinder which intersects the surface of the thread in such a manner that the intercept on a generator of the cylinder, i.e. the tangent circles in your sketch from step 4), diametral pitch (number of teeth per inch of the pitch diameter), and pressure angle (angle between the tooth face and the gear wheel tangent; either 14 or 20 degrees as standard). In order for two gears to mesh, they must have the same diametral pitch and pressure angles. This means that if you have two gears with different pitch diameter (so one is larger than the other in radius), one must have more teeth for them to turn each other (so that diameter pitch, teeth per inch, is the same). One calculation to know: number of teeth divided by diametral pitch = pitch diameter. For example (see 7th image above), a gear with 1/2" pitch diameter and diametral pitch of 24 must have 24 / (1/2) = 12 teeth. If applicable, you should make your hub diameter (i.e. radius of inner circle of gear) the same as your bolt's diameter so your gear will have holes. Otherwise, you can manually change the circle's diameter in your svg/graphic file later on.

To generate the gears, I used Solidworks since I wanted to provide pictures of the 3D structure, but you can use free resources like geargenerator.com to get svg files. Follow the example above for calculating the specs of each gear based on the sizes of the circles in your sketch from step 4.

Tip with wooden gears: the higher your diametral pitch, the better they'll spin together. I learned it the hard way, but here my example has 24 as diametral pitch. I ended up going up to 36 and 40 for better gear trains.

Step 7: Part 4: Mating Gears to Sketch

This step is just for people following on Solidworks and want to visualize their gear train: you'll need to mate your gears to the sketch, as it center them and make sure they're all lined up. Follow the step-by-step instructions in the notes above to see how I did mine.

Step 8: Part 5: Generating Gears With Internal Teeth

Gears with internal teeth work basically the same as the spur gears from part 6: just calculate the number of teeth required similarly. The option in Solidworks is right next to the spur gear icon, so just drag it in and change the parameters. I forgot to sketch the pitch diameter circle for my internal gear, but it's just 2" so my number of teeth is 24*2=48. Since I wanted to have teeth on the inside and outside of this ring (see gear in gear train 1), I generated a spur gear around it (third and fourth images above). Then once I export the files for these two gears, I deleted the inner circles to get one full gear with internal and external teeth.

Step 9: Part 5: Saving Gears for Laser Cutting

To get the gears into a format recognizable for laser cutting, I exported the faces as .dwg files (commonly used in AutoCAD, similar to .svg files and can be read in Adobe Illustrator). See the step-by-step instructions in the notes above to see how I did this.

Step 10: Warning: Exporting .dwg Via Engineering Drawings

For those who are familiar with SolidWorks and know how to export .dwg files via engineering drawings, DON'T DO THAT. If you create an engineering drawing file from your parts and import that .dwg into Illustrator, all your gears will be exploded (lines aren't joined). This makes rearranging your parts difficult, since you'd have to click each line and group them before dragging them around. Another thing about importing the engineering drawing is that the lines are pretty close, and that could put you at a higher risk for starting a fire from laser cutting such close lines. It might not be a big issue, but since I was using a school laser I didn't want to take chances.

Step 11: Part 6: Generating Support for Your Train

The gears need some support for the bolts to go through and thus keep the gears in place (see the cross in gear train 1, for example). This really depends on how you designed the support for your gear train as explained in step 4. in the above pictures, I just walk you through how I extruded out a simple shape to get my cross design in gear train 1, and how I extruded an extra shape to get the background circle with bolt holes for gear train 3, but adapt these ideas to however you designed.

UPDATE: 12/20: something went wrong with uploading my png's for this step; to be updated in just a bit when I have time to crash a computer lab!

Step 12: Laser Cutting

Once your designing and files are finished (*phew*), laser cut your gears at your local makerspace or get them cut online at places like Pokono.

Use sandpaper to get rid of any residual scorch marks!

Install your bolts and nuts wherever you designed them, and test your gears to see if they turn! Hopefully they do; if not, watch each gear carefully for troubleshooting. Sometimes it may just be that the laser cutting tolerance was such that your cut gears ended up a bit too small, so you can just make them a little bigger and re-cut.

Next steps are now just on wood staining and files for my gear train designs.

Step 13: Wood Staining

You can use different woods and wood stains to make your gear trains more visually appealing. Acrylic also adds more variety, too; see all of my examples from the intro step!

If you don't have any materials for staining wood, fear not! Markers (sharpies in my case) can provide bold colors (second picture above). Alternatively, food coloring mixed with rubbing alcohol (I put 2 drops per 1 teaspoon) works great too (third and fourth pictures above).

Different woods will look different for the same "treatment" that you use, so make sure you test your staining before use! See the last image above for example: I had regular plywood from Home Depot and also Russian birch plywood (specially made for laser cutting) which had different colors when stained.

When staining, consider how you'd like your gears to be differentiated for the final toy. See the gif above: I had simple color schemes but put them on different faces and components to make the toy more interesting.

Step 14: Gear Train 1

Attached to this step is the .ai file for gear train 1. Simply cut out the gears on eighth inch material and use four each of bolts and nuts.

See the notes in the pictures above for step-by-step instructions on assembly.

Warning: this design doesn't spin too well because I only later realized that increasing diametral pitch would reduce clashing.

Step 15: Gear Train 2

Attached to this step is the .ai file for gear train 2 (the layer called version 2.0 is the one with higher pitch diameter to make the gear train spin better). Simply cut out the gears on eighth inch material and use four each of bolts and nuts.

See the notes in the pictures above for step-by-step instructions on assembly.

Step 16: Gear Train 3

This gear train is the most complex of all so follow the pictures above to see the assembly. Just know: I only have have four different gear sizes (36 diametral pitch with 18, 24, 36, and 48 teeth -- there should be 4, 3, 5, and 1 of them, respectively) so match up which gear goes where using the images above (and reference Solidworks image in the last image above!)

This is where I should've been more careful with balancing my load. I originally wanted to drive everything off the top gear, but looking at the design, it makes more sense to drive everything from the right most large gear (see all gears in last image above).

There are two layers in the file: "quarter inch" for cut on quarter inch wood and "eighth inch" for cut on eighth inch wood (or acrylic! I used black acrylic in one of them). You can cut everything on quarter inch, but just cut 2x of the quarter inch designs and glue them together to get quarter inch. The four short gear segments are stacked and glued together to get the random teeth sticking out from the edges. The tiny gears (three in eighth inch layer, two in quarter) are just for decoration to fill up void space on the edges.

Let me know in the comments section if you need assistance!

Step 17: Future Directions

These are great gifts for Christmas, as just small fidget toys and such, but that's not all! I designed awards for a mechanical design challenge and incorporated the gears to make them kinetic, for example (see images above). Other things to think about:

• I really wanted to design a lamp that could be turned on by rotating gears. It'd probably be a contact switch somewhere to keep things cheap, but it's in my sketchbook for later!
  • see this link for really awesome examples.. #goals
• Mounting gears on lit up surfaces makes for an interested effect (see second image -- those gears are made of metal so they don't shine with the acrylic background, but imagine if they were acrylic too....
• I mostly used wood, and wish I could have cut more with acrylic. The gears actually spin so much better with acrylic, perhaps from less friction... point is, try different materials! Waterjet some metal gears if you can for some nice, high pitch clinking sounds (yes I've done it and it's so nice...)
• My designs for the gears are mostly cutouts, but engraving designs would look nice too. I just did cutouts because they were faster to finish (and technically I shouldn't use school lasers to do personal projects..).

The possibilities are endless!