For my Mechanisms Midterm I needed a good way to make both cams and circles out of wood. However, all the attempts that I had made previously lacked the roundness that I needed in order to get good motion. Upon reading more about wooden mechanisms / automatons…I came upon a post talking about various tools to use in order of ease for cutting out wooden circles (The post of course I have since lost…but will be referenced once I find it!). This technique can be used with a range of wood widths, and can create various circle and cam sizes.
First, I built a Circle Jig, which just included measuring in various increments (1″, 1.5″, 2″, 1.75″, 1.25″ and .75″) away from the edge of a wooden board…and drilling a 5/16″ hole at each of these locations. 5/16″ is the size of dowel rod I had at the time, but this size also made sense to me because in order to make a circle a small hole needs to be drilled into the center of a piece of wood (more on that in a moment).
Steps to Make Wooden Circle:
2. Drill 5/16″ hole (or whatever dowel size you have chosen) into a piece of wood that is just slightly larger than the circle size you plan to make. Try to drill this hole in the middle of the piece…but if the hole is off by a bit it should still be alright as long as the piece of wood is sufficiently large
3. Place dowel rod through wooden piece and into the clamped Circle Jig. If the wooden piece is unable to fit with a little bit of clearance with the belt sander, use the sander to remove material from the wood (Your piece of wood should be able to stay in one place on the circle jig attached by the wooden dowel without moving if the belt sander is running).
4. With belt sander running, slowly rotate wooden piece around dowel rod with your hand (being sure to stay away from the sander). Move slowly so that the sander takes away the material without putting undue stress on the machine. Continue to rotate the dowel until you have a circle.
That’s it. The process kicks off a ton of Sawdust, so you should wear both safety glasses and a dust mask. The circles I made were just off of perfect (slightly flat side from starting the shape) but function well enough in creating mechanisms. The whole process takes about 5 minutes, and can make a wide range of circle sizes (though I made mostly circles in the 2″ to 4″ range). Keep in mind that the circle will be twice as large as the distance from the belt sander…which means it is difficult to make smaller than 2″ circles.
Cam making works in much the same way. From my observations, a Cam is basically a combination of two circles with different radii, connected by a bit of a flat part. First figure out what the radius for each circle should be, and how far apart the center will be in the end.
Then, just like with the wooden circles above, drill a hole at each center point.
Once one side of the cam is made, turn off the belt sander and switch which hole in the cam the dowel is in, and also the hole in the circle jig. You should then create the second side of the cam just as you did the first, except you should rotate less than 90 degrees…only rotate it so that at maximum the edge of the larger circle is shared by the smaller circle (one straight line from the small to the large circle). This should be done on both sides.
You can then sand down both of the flat parts to ensure there is a continuous smooth path along the edge of the cam.
Hope that Helps!