|Project by DickB||posted 06-18-2013 01:49 PM||2108 views||8 times favorited||13 comments|
Synchronicity is an exposed wood gear clock with a novel drive mechanism. Like one of my previous clocks, it uses an electromagnetic pendulum drive. A rare earth magnet is hidden in the back of the pendulum. As it swings past a coil hidden in the clock’s back, a battery-powered circuit detects this and injects a pulse of current, repelling the magnet and giving the pendulum a push. A microcontroller measures each and every swing of the pendulum, and slightly speeds up or slows down the pendulum as needed, so the clock keeps perfect time.
I used Baltic Birch for the wheels (large gears) in previous clocks, but this time I wanted to give the gears more character, so I used 7/16” oak. Blanks were made up from eight pieces of oak wedges. I glued together four wedges at a time to make halves of the blanks, then sanded the sides of the blank halves to be glued to each other together. This corrected a slight error in the angle of the wedge cuts. The blanks were then raster carved to produce the hub and spokes, and the teeth vector cut.
The clock was entered and won a recent Carvewright contest. All of the parts were designed using the Carvewright Designer software and machined using the Carvewright CNC machine. Only a 1/16” ball nose carving bit, a 1/8” straight cutting bit, and a 60 degree V bit were used.
Most of the gears ride on brass bushings made of hobby brass tubing, but key parts such as the ratchet wheel and second hand shaft, and pendulum, are on bearings (like RC car bearings). A cam at the pendulum pivot is used to drive the moving pawl. This limits the travel of the pawl, regardless of the angle of swing of the pendulum, the latter of which is varied to regulate timekeeping.
The clock was designed to be a wall clock, but Carvewright intends for the contest-winning projects to travel to trade shows and the like. So I built a stand for it for more convenient display. I also built a shipping box to ensure the clock could travel safely. And I made a video for the contest, to highlight features of the clock and illustrate some of the design and build process:
A variety of woods were used: mahogany back, oak wheels and pawls, maple frame and pinions, pine face and pendulum, hickory bob and stand, and walnut hands. No stains were used, just three coats of satin lacquer, the final coat out of a spray can.
I have a few tweaks to make to the design to make the clock a bit easier to build. Once I do that, I intend to put the design into the Carvewright Pattern Depot for others to build. (Sorry, Carveright files use a proprietary format, so it is not possible for me to convert to DXF for other machines.)
-- Dick, http://www.carveshop.com