Chapter 11: The Dial & Motion Work
March & April, 2006
This chapter covers the making of the dial, the entire motion work (which converts the motion of the minute hand to run the hour hand), and the hands.
The book includes plans for a somewhat fancier dial that consists of two grooved rings with brass Roman numerals soldered between them. My lathe isn't big enough to make it, and I didn't particularly want to bother ordering the numerals either, so I designed a slightly simpler one, where the "big" parts could simply be cut from sheet brass. Here you see pictures of the clock frame with the finished dial installed, and with the marked "blank" before most of the work was done. The 'pips' in the dial are actually small pieces of chamfered steel rod, which have been blued and riveted in place in the dial. It makes for a nice shiny & colorful effect.
To the left is a shot of the riveting for a dial pip. It's a bit messy, but is only visible from the back, and does a good job of holding the pips in place. To the right is a shot of one of the four pillars that holds the dial off from the front plate. These are all cut by hand using a graver from thin brass rod. The ends are tapped with 0-80 machine screw holes for mounting to the dial and front plate.
The motion work requires two identical 39 tooth wheels, and shortly after I finished the blanks for them, I realized that I actually had brass rod that was large enough diameter, so I decided to use that instead... and try cutting them both at the same time! The picture on the left shows how this worked - I used a parting tool to groove the rod between the "gear blanks", and then simply cut the teeth normally. I had only enough room to cut two before the cutter would have hit my chuck, but I only needed two so that was fine. Once the teeth were cut, I "sliced off" the finished gears with a parting tool. It worked like a charm, and saved me a bunch of tedious tooth cutting. The picture on the right shows the lathe setup I used to cut the teeth. This setup is much better than the older one I used to cut gear teeth, because the weight of the motor is mostly centered over the lathe bed. This makes it much easier to move the cutter back and forth, and more accurate to boot.
Here are pictures of the finished 39 tooth wheels. The one of the left will be made into the minute wheel, once the pinion is attached. Note the nice pattern on the face of the wheel - this is from the gear teeth causing some vibration when the wheel was parted from the rod (as described above). The picture on the right is of the other 39 tooth wheel, which has been used to make the canon pinion. The square filed into the end of the canon pinion pipe is barely visible - this will turn the minute hand.
Here's a shot of the finished hands. The book describes how to cut them out of steel sheet, polish and blue them. I was in a bit of a hurry, and didn't have any steel of the appropriate thickness, so I made them out of brass instead and painted them black. I suppose horology purists may be appalled, but I think they look perfectly nice. The hour hand is riveted to a small brass collet, which holds it onto the hour wheel pipe.
Finally, here is a picture of the completed motionwork, installed in the clock. There are a number of small parts I didn't photograph here - the washer and pin in front of the minute hand holds everything in place. Behind the canon pinion there is a bow spring that provides a sort of "friction clutch" between the hour and minute hands. The minute wheel now has a small lantern pinion attached, as well as a steel arbor that screws into the front plate, and a small nut to hold the wheel in place. The shop manual indicates that the hour wheel should be spoked, but I forgot until after I'd already riveted it to the hour wheel pipe. It's small enough that I'm not too concerned. Good news: the motion work appears to run smoothly, despite some of the pins in the minute wheel pinion getting slightly bent during finishing. Oops.
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