Making Basic Gears: Tutorial
*****THE FOLLOWING ENTRY IS IN PROCESS OF BEING EDITED****
Curious about how to make your own gears? This tutorial explains a very basic process of how you can use Sketch Up to design gear shapes that will be exported into Illustrator for laser cutting. The gears we will make are "Involute Spur Gears." Spur gears are the simplest type of gear. Their general form is a cylinder or disk with teeth projecting radially. These gears can only mesh correctly if they are fitted to parallel axles. Involute refers to the contour of gear teeth curving inward.
This tutorial is not expert advice. The following information is based on my process of making gears as an artist curious about how to construct objects that move. I greatly appreciate any advice or thoughts others have, and as I explore more techniques, I will continue to update all this information.
WHAT YOU'LL NEED TO GET STARTED
-Involute Gears Plugin (it's free!) http://www.ohyeahcad.com/download/
-1/4" thick masonite laminate both sides, no larger than 18" x 32"
-laser cutting facility (Advance Media Studio at NYU)
HOW TO DESIGN SOME BASIC GEARS
Before you begin, download and install the free gear plugin for Sketch Up. When the plugin is correctly installed, you will access it under the "Draw" menu in Sketch Up.
You will see two options: "Involute Gear" and "Key Involute Gear." Play around with both of these options to see what works for you. "Involute Gear" option is more basic and does not give you a center point. If you use this option, you will need to measure and place your own center point later in Illustrator, taking extreme care to be accurate and consistent. "Key Involute Gear" will give you a center point, but you will still need to place your own center point in Illustrator (you will understand why later). The only advantage is using the point made in Sketch Up is that you can use it as a guide later in Illustrator.
The following is an explanation of the settings you can adjust:
number of teeth = the number of teeth around the outside of the gear
pressure angle = the complement of the angle between the direction that the teeth exert force on each other, and the line joining the centers of the two gears. For involute gears, the teeth always exert force along the line of action, which, for involute gears, is a straight line; and thus, for involute gears, the pressure angle is constant.
pitch radius = can be considered sort of an "average" radius of the gear, somewhere between the outside radius of the gear and the radius at the base of the teeth.
shaft radius = determines the size of the center hole
key width = width of the key "stem" shape
key depth = length of the key "stem" shape
Keeping the pressure angle constant, scale the number of teeth and the pitch radius proportionally. For example, a series of gears would look like this picture .
After you have created a series of gears, go under File/Export and export your file as a 2D Graphic (EPS file).
Open this EPS file in Illustrator.
Unfortunately, things get a little weird at this point. You'll notice that the scale of your file in Illustrator is extremely small  This is why worrying about the size of your shaft radius in Sketch Up is a waist of time for anything other than use as a guide.
Select all the gears and scale them all up until you have reached a size you are happy with . Determine measurements using the rulers in Illustrator (View/Show Rulers). Make sure you scale all the gears at the same time to maintain proper proportions. If you do not do this, the gear teeth will not mesh correctly .
When your gears are the desired scale, select all and "ungroup" them (Object/Ungroup). This will separate the solid areas from the outlines. Select the solid areas of each gear and delete them, so that only the outlines of each gear remain. Using the "direct select" tool, select each gear outline one at a time then copy and paste the gear, and Group (Object/Group) the points of the pasted gear . Repeat this process for each gear. This process ensures each gear is independent from others. Delete the original gears after you have created the new independent gears .
At this point, you have clean, separate individual gears. You may wish to resize them again, just remember to select all of them at the same time when adjusting scale. Assuming you are pleased with the scale, you will now create the center holes. It is imperative that the center holes are exactly center. I suggest making the hole first. Let's start with a 1/4" hole intended for a tight fitting 1/4" shaft. Using the rulers, guides and grid view in Illustrator, make a .1pt stroke circle measuring 1/4" . Place this circle off to the side. Now line up all your gears so that they share a common center . Place your 1/4" circle in the exact center of the gears . Take turns selecting each gear with the center hole. Copy, paste, and group the combinations  so that you have each independent gear with a center hole .
Now you have some gears! Let’s set up a laser cutting file.
Refer to this link for a guides and templates for laser cutting: http://www.nyu.edu/its/ams/#laser
Basically, you are going lay out your gears in a template supplied by AMS, being sure to measure the dimensions of your material (masonite) accurately, ensuring it is no larger than 18" x 32" or thicker than 1/4". Select your gears and make sure all the outlines are at a .1pt stroke and colored R:255, G:0, B:0 (you can select the color from the laser cutting template using the eyedropper tool) for cutting. These specifications are necessary for the laser cutter and AMS will not accept files that are not created following these specifications. Copy and paste as many gears as you can fit (leaving a 1/4" frame around the material bed) in whatever numbers you desire .
Suggested additional supplies for gear assembly include:
-dowels (size depends on the diameter of your center holes. I used 1/4" and 5/8" sizes)
-wire 20 gauge (wrapping the wire around the shaft works great as a quick sleeve to keep your gears in place)
-graphite (to lubricate the wood and help smooth out the friction between the gears)
Now that you have a set of gears with different ratios, you can explore the infinite ways of assembling them .
Consider playing with the following:
- Using dowels as shafts, play with their relationships to the gears. One relationship is a loose fit, meaning that the gear center hole diameter is slightly greater than the shaft diameter, allowing the gear to spin independently on the shaft. The second relationship is a tight fit where the gear and the shaft are joined together, therefore turning together. This enables gears of different sizes to move at the same speed.
- Glue together gears to create thicker widths and design custom gear forms .
- Using a scrap wood board, measure and drill holes to learn the exact distances between the center points of your different gears . Establish a chart that you can refer to so that you are better able to construct systems with multiple gears. Gear systems are rigid and exact. If one gear is slightly out of alignment, the system will not work.
Play around! Consider your first set of gears as blocks to play with to get a feel for when and why gears work well and don't. Do not expect perfect results the first time around. Allow time and mental space for error, adjustment, and revisions.
It is not possible to design a gear tooth profile which rolls through the mesh without friction. Service life is often managed by using hard materials and constant lubrication. Materials like plastic and metal are generally better to work than wood with to minimize trouble with friction. Variables like weather and time can also affect wood and make it difficult to maintain optimal functionality.