Print PDF
Favorite
Email
Step 5Designing The Gears
When designing gears, there are many parameters that can affect the size. I took some of the standard values for the variables when making the calculations. I used a pressure angle of 20 degrees, and a Diametral Pitch of 8. These combined with the number of teeth of each gear, I was able to calculate the Pitch Diameter, Root Diameter, Outside Diameter, and Base Circle Diameter.
Now that I have the Diameters of the gears, I can start drawing them. I found instructions on drawing gears with CAD and followed them to draw these gears. It was written by Nick Carter. A link to his page is in the last step in the References Section.
The free2Design file has the Gears and Pinions with a layer that shows the lines drawn to create the teeth. While researching clocks, I came across Gary's Clocks. He mentioned that there is a big difference in what you can draw with CAD and what you can actually cut using a scroll saw. I learned this the hard way. Cutting the gullet between the teeth is a bit tedious. To try to speed things up I decided to add circles between each teeth to be drilled out with the drill press. That saved time trying to round out the valley between the teeth, but I think it caused some problems with the teeth meshing with each other.
Along with the gears are the Escapement and the Ratchet Mechanism. As stated earlier the Escapement is a mechanism that allows the energy to escape slowly. This is done using a gear, lever and pendulum. What hasn't been talked about yet is the Ratchet. We said that a weight is wrapped around an axle with string, and it slowly lets out to drive the clock. We need a way to re-set this, or wind the clock. The Ratchet will allow us to do that. It fits loosely over the axle of one of the gears, and pushes against the gear with a pin and lever. When the clock needs to be wound, the Ratchet can be turned counter-clockwise without moving the gear. Then when the weight pulls it clockwise again, it catches on to the pin fixed to the gear, and continues to power the clock.
Now that I have the Diameters of the gears, I can start drawing them. I found instructions on drawing gears with CAD and followed them to draw these gears. It was written by Nick Carter. A link to his page is in the last step in the References Section.
The free2Design file has the Gears and Pinions with a layer that shows the lines drawn to create the teeth. While researching clocks, I came across Gary's Clocks. He mentioned that there is a big difference in what you can draw with CAD and what you can actually cut using a scroll saw. I learned this the hard way. Cutting the gullet between the teeth is a bit tedious. To try to speed things up I decided to add circles between each teeth to be drilled out with the drill press. That saved time trying to round out the valley between the teeth, but I think it caused some problems with the teeth meshing with each other.
Along with the gears are the Escapement and the Ratchet Mechanism. As stated earlier the Escapement is a mechanism that allows the energy to escape slowly. This is done using a gear, lever and pendulum. What hasn't been talked about yet is the Ratchet. We said that a weight is wrapped around an axle with string, and it slowly lets out to drive the clock. We need a way to re-set this, or wind the clock. The Ratchet will allow us to do that. It fits loosely over the axle of one of the gears, and pushes against the gear with a pin and lever. When the clock needs to be wound, the Ratchet can be turned counter-clockwise without moving the gear. Then when the weight pulls it clockwise again, it catches on to the pin fixed to the gear, and continues to power the clock.
| « Previous Step | Download PDFView All Steps | Next Step » |
Or join their beta program and get their beta software.
http://www.a9tech.com/a9cad/
Unfortunately, it does lack certain advanced features that would make your design work a lot faster.
For example, in the case of designing these gears, it would be handy to have a "Polar Array" feature. That's where you select an object or group of objects, Pick a center point, tell the program how many duplicates you want and how many degrees you want it to cover. The program would then automatically rotate and place the objects for you. So, you could draw one tooth of the gear, tell the program how many teeth you need and where the center of the circle is and it would draw the whole gear for you.
Alas, with A9CAD, you would have to draw each tooth individually. :(
Still, it is free and it is effective. I was trained on AutoCAD at work, but couldn't afford a license for home. A9CAD is a good free substitute.