Design and Modeling
For my project, I built a clock in which when the crank on the back is spun, the minute hand goes around and the hour hand follows at 1/60th the speed. To accomplish this, there needed to be a central axis (minute hand) which the crank would spin and a second axis (hour hand) wrapped around the other axis which would be moved by gears. Using gear generator, I was able to figure out a tooth pattern with 4 gears that would accomplish an approximately 1/60 reduction. Using this information, I drew up a quick diagram in photoshop representing what I would be modeling in illustrator.
photoshop drawing of the 3 parts of the clock mechanism
left shows the parts to be laser cut, right shows the virtual assembly of the parts
Test Cutting
To get gears to fit perfectly around axles and the secondary axle to fit well within the front plate, I had to experiment to figure out the perfect gap between parts, which turned out to be .01 in. For example, the wooden dowel axle was measured to be .36 in in diameter and the perfect diameter of holes would be .37 in. This required a few attempts, pictured below, to finalize the design for my cuts. I also added teeth on the inside of the gears that would catch on the dowel, keeping them aligned.
Final Cut
Preparing for Assembly
In my design, I prioritized aesthetics over a guarantee of perfect function, so I wanted the tightest tolerances in order to have a slim, elegant result. To do this, the wooden gears would be in constant contact with each other, the front plate, and the back plate. To get them to move more smoothly, I sanded every area which would contact another gear to 320-400 grit, extremely smooth. The burnt areas between gears which I could not sand seemed to have high friction, so I sprayed clear coat over them, which seemed to have worked decently. I dremeled the notches in the dowels to allow gears fit on.
the 3 segments of the round sides of the clock frame, clamped together while gluing
Final Assembly
In the final assembly, I started gluing parts together and making sure everything was aligned. After making sure the glue would hold and that the hands would spin properly, I glued the front and back plates together with the side pieces, locking everything in.
a test fit showing everything together
The result
The clock, in my opinion, looks amazing. However, there are some problems with the gears that make them frequently stuck and to get around this, the exposed gear on the side has to be moved with the crank. The problem, I believe, is that there are millimeter small issues with alignment on the gear holes that moves them around unnecessarily. Also, the gears might be a bit too far apart. The last thing I did was vinyl cut black hands for the clock because I was forced to, but in my opinion the clock looks best with full wood.
Cost Estimate
Labor: $8 hrs at $30 an hour
Materials: $17 – $10 approximate for the slab of plywood used, $2 for the wooden dowel, negligible glue use, $5 in sandpaper
Total: $257
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