# Project Report: Fabrication

This past week I finished up my project and prepared to present it at the expo. Once I had completed the design the first step was to laser cut my pattern on 5mm birch plywood. The laser cutter managed to cut through the wood, but I would estimate that 5mm (.197 in) is close to the maximum material thickness. I then glued together the layers of the wooden clock using Titebond I woodglue.

The next step was to coat the plywood sheets with a layer of wood stain and then several coats of shellac. The wood stain improved the appearance of the wood and the shellac serves as a protectorant and adds a glossy appearance.

The drive train was composed of 3D printed gears. In the future I wouldn’t use 3D printed parts. The gearing required much more precision than my 3D printer could deliver. As a consequence I had to sand down many of the gear teeth to reduce friction in the drivetrain. Intially, I used a 1kg weight to drive the clock, but there was too much friction in the system. The mechanism worked reliably after increasing the weight to 2kg and polishing the gear teeth. The clock was designed to run approx. 2.5 days. Next time I would use a more forgiving gear ratio. Additionally, I would like to add a motorized autowinding mechanism.

Design Calculations:

For the pedulum I used the formula for the period of a compound pendlum. Instead of integrating the mass of the escapement and rod, I treated the pendulum as two point masses. The bottom weight is adjustable up and down so the clock speed may be tuned.

T = 2π √(I/(mgR)), R = distance from pivot to COM

As for the gearing, the clock is contains 7 gears including the escapment. The overall gear ratio is 200:1, given that the weight string is 5′ long this allows the clock to run for roughly 2.5 days

5ft string, 1” cylinder – 19.1 Rev in

G1 = 60 T

G2 = 18T

G3 = 64T

G4 = 8T

G5 = 60T

G6 = 8T

E7 = 30T (60s per rev)

19.1 Rev in => 3820 Rev out

63.67 hours runtime (2 days 15 hours 40 minutes)

This video shows the final product!

• Derek Sikora
May 2, 2016 11:04 am

The shellac coating on the wood brings a nice warm finish. Typically I would suggest to be careful with the tolerances on 3D printed gears due to the expansion of material that occurs, but you seemed to have figured that out. Nice work!