Chapter 10: The PendulumNovember 20th, 2005 - February 18th, 2006
This chapter covers the making of the pendulum bob, pendulum rod, the weight used to drive the clock, and the small pulley assembly used to reduce the drop height of the weight.
First up was the pendulum bob. This was supposed to be made using a lathe technique called "spinning metal". You basically mount a sheet of metal on the lathe, slather it with soap and motor oil, and then bend it into shape as it's spinning. I hear you can make all sorts of pretty round cross-sectioned things this way, but my experiments were a complete failure. I finally resorted to standard small metals technique and hammered the flat brass disks into shape. You can see at left the plywood form and home-made dap I used to shape the metal. Each side of the pendulum bob needed to be annealed about a half dozen times before it was finished. Then the two sides were carefully joined by sanding flat, bound with wire, and soldered together using silver solder. The solder isn't perfect (there were some gaps too large for it to flow), but it's not bad. Notches were formed for the pendulum rod, and a hole was drilled in the back for pouring the lead. The molten lead was poured with a dummy pendulum rod in place, so that there would be a space left for the real pendulum rod once it was completed. Finally, the pendulum bob was sanded smooth (there were lots of dents) and laquered to prevent tarnish. Below are pictures of the pendulum rod and the finished assembly. Not pictured here is the little "rating nut" that screws onto the bottom of the pendulum rod and prevents the bob from falling off. The timekeeping speed of the clock can be adjusted by twisting this nut, which raises or lowers the pendulum bob.
Next up was the weight. This is a poured lead weight, and was much easier than the pendulum bob. The shell is made out of brass tube, cut to length. It was difficult to cut on my small lathe, since I didn't have any way to support the end, but I managed to keep it in place with only my three jaw chuck. The shell was lined with paper, and had plywood with cardboard spacers bolted on to the top and bottom to keep the lead from leaking out. The bolt served double duty as a placeholder to leave room for the final rod that holds the weight together. The small pan I've been using to melt the lead wasn't large enough to do it in one pour, so it actually took several. You can see the "seams" in the picture of the finished lead weight, where the weight cooled and I poured more molten lead on top. Below is a picture of the completed weight, and the various fittings that go with the shell. The top "plug" has a ring on it, which will be used to hang it from the pulley assembly when the clock is in operation.
The last stage of this chapter involves making a small pulley assembly that attaches to the top of the weight. Above you can see the sides of the pulley assembly cut out and marked with layout blue, as well as the pulley wheel itself. Below is are pictures of the fittings (so you can see how it's put together) and the finished pulley assembly. Somehow I get a real thrill from riveting things together, and it was great to assemble the pieces of this pulley. I actually outsmarted myself a bit with this one, though. I made the round top piece (which the hook screws into) slightly wider than it was supposed to be. My thinking was that the extra space would ensure that the wheel turned smoothly. However, I forgot this when cutting the groove for the "C" clip in the steel bottom rivet, and so it was necessary to bend the sides together very slightly in order to get everything to fit together. Oops. The pulley turns without trouble, though, so I think it will be fine.
The best thing about this chapter was the testing at the end - the moment of truth! I've been working on this project for over a year without knowing if my clock would actually run, and it was finally complete enough to find out! I put together a simple test rig, and assembled the clock using a random piece of string as a temporary weight line. Much to my pleasure, and somewhat to my surprise, it ticked away without trouble. My clock actually runs! I left it running for an hour or so, showing it off to the household, some visiting friends, and Elmer our friendly neighbor who happened to be walking by. I didn't want to leave it running any longer, since none of the bearing surfaces have been oiled. Here's a shot of the clock in action, on the test rig.