I have always wanted to work with gears. A gear or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part to transmit torque, in most cases with teeth on the one gear being of identical shape, and often also with that shape on the other gear. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source.

When I first got my 3D printer I made a 3D printed grandfather clock.

The clock worked ok. I printed the parts on a machine that was a little small for the design. The machine would work for a short time but I was able to see how the parts work. But I still wanted to design and build a machine of my own.

Several people on Thingiverse, a website dedicated to the sharing of user-created digital design files, have various models and scripts that create gears and gear based machines. I feel as I explore more mechanical design ideas, I will need to explore basic simple machines like gears to fill in gaps between motors and the work I am trying to drive.

On Thingiverse the user Leemon Baird shared his script to generate Public Domain Involute Parameterized Gears.  This script simplifies lots of the details. For example, according to wikipedia, details like the angular velocity ratio between two gears of a gearset must remain constant throughout the mesh.  That sounds difficult and would overwhelm someone new to making gears.  Leemon made a function that takes 9 parameters but you only need to enter 4. These variables are: the circumference of the pitch circle divided by the number of teeth (millimeters per tooth), total number of teeth around the entire perimeter, thickness of gear in mm, and diameter of the hole in the center in mm. With this basic script to went to task laser cutting gears out of thin plywood panel. I had to goal but to see how many I could put on a board and see hard/easy to drive the gears.

As you can see from the picture above I made a lot of gears. They were a little rough to drive all of them at the same time. I was having alignment problems as well. As I was moving the gears some wouldn’t engage. I placed an acrylic guide over the main drive gear, the one with the handle, to try to resolve the alignment issue. And the gears where attached by 3mm bolts. So the entire surface of the gear was rubbing against the attached panel.

After the laser cut gear experiment I had a few lessons for my next attempt. First, I need the cut the gears out of thicker material. The laser cutter is nice because I just load in the parametric design into the computer and cut, but the laser can only go through thin material. Second, I need to keep the gear floating above whatever it is attached to so I don’t get that surface drag. And third, I need the gear to use bearings and bushing to reduce friction on the fastening bolt.

 CNC Panel Router

So to cut out gears out of thicker material I need to learn a new tool. And that tool is the stinger CNC router.

A CNC router is basically what it sounds like. The machine has a router mounted on an arm that moves in the X,Y and Z axis and the arm is controlled by a computer. You can load a computer design file into the computer, the computer will determine the tool head path based on the design file and the type of bit on the router. This machine can use the same files I generated for the laser cutter, but can cut through up to 3 inches of wood. There is a little more setup involved that the laser cutter. The laser beam is a simple point and doesn’t change, it simply follows the line. The CNC router is a bit that can be one-eighth to three-quarters of an inch thick. So when you define the tool path you need to specify whether you follow the inside or the outside of the line.

The CNC router also allows other options that a laser cutter doesn’t. First, you can specify the depth that you can cut down. You can cut all the way through or just a shallow cut. Second, there are different drilling profiles. You can drill hole, a pocket where all material is cleared away, cut on the inside or outside of a profile, engrave a shape into a surface, or cut a relief on a surface.

For the gear I needed three things, the ability to a gear profile out of a piece of three-quarters inch plywood, drill a hole through for a bolt and bushing, and a pocket for a regular skate bearing. I was able to take the files from my lasercut gears and use them to generate some vector files for routing. I can select each line in the vector file and create a different cut style.  For example I can select the teeth profile and tell the software to route all the way through the plywood from the outside of the line. The inner two circles have a different cut path. The center most circle will cut all the way through from the inside of the circle. And the outer circle will cut a pocket half way through the plywood. Below are some pictures showing the a vector art being loaded into the tool path generation program.

I configured the tool path generation to use two different bits. The Teeth profile and center circles can be cut with a single end-mill bit. This bit will leave straight edges. The lettering will be engraved with a 90 degree V-bit. After generating the tool path and then saved out the commands into two files. I am now able to load the tool path data into the CNC router driver software.

Once to plywood is loaded onto the machine and the bit head is aligned and configured I can let the machine cut out the parts.

Once I can take off the gears I just need to place in the bearing, screw on the bolt, and attach a magnet to the bolt so the gears can attach and slide on a metal surface.

And here is the final product.