Free Counter
This clock runs for a week on a weight which scales in at a little more than one pound. That shows how efficient the escapement is.
I determined the weight required to run the clock by powering it with a small tin can loaded with lead shot. I adjusted the amount of shot in the tin until I was happy with the amount of balance rotation.
Then I had to make a finished weight the same mass as the tin can and shot. Using geometry, I determined that a solid lead weight would equal about half of the volume of the same weight of lead shot. (A cube contains about twice the volume as a sphere of the same dimensions, so a solid weight would have about half the volume of an equal weight of lead shot.)
So, again using geometry, I determined that a piece of 1.5" tubing about 1.75" high would contain the necessary volume to hold a little over a pound of solid lead. So I planned on making a weight from 1.5" brass tubing.
The top of the weight shell is made from 1.5" solid brass. Using the lathe, I made a cut in the brass about 1 and 3/8" in diameter, the size of the inside of the 1.5" brass tube and about 1/8" deep. Actually, I made the 1 and 3/8" cut about .002" oversize, so that I can press-fit the top onto the tubing.
Then I put the preliminary top and tube in one pan of a little balance scale, and put the tin can with its lead in the other pan. Next, I poured more shot into the side of the scale with the preliminary top and tube, until the scale balanced. The shot I had just poured into the pan should be the amount of lead required.
Next, I pressed the top of the weight onto the tubing, using a large vice to scrunch it on.
Now that I have a container in the form of a top and tube with the top pressed tightly on, I melted the shot in a tin can on top of an ancient Sears gasoline camp stove, and poured it into the shell. The top has a knob on it, which I held in the large vice while pouring. (Like your mother said, "Use adequate ventilation when pouring molten lead.")
When the lead had solidified and cooled, I machined flat the inside end of the lead in the shell. (Lead can be machined, if you use sharp tools.)
The glass dome for this clock is large and expensive, and a free-swinging weight is dangerous to glass, so I made a track for the weight to ride on. The weight descends on a 3/32" music wire rod, so it must have a hole drilled lengthwise through its center for the rod. I drilled the hole through the lead center with a 1/8" drill.
To drill lead, the drill must be sharp, kept well lubricated with cutting oil, and withdrawn often to remove chips. If not, the chips can bind up in the hole and seize the drill bit.
Then I made a weight bottom similar to the top, and pressed it onto the shell as well. Now I have a weight.
I made spigots on both the top and bottom of the weight to make it easier to hold it in the lathe for finishing. One spigot is clamped in the lathe chuck, while the other end is supported in a live center in the tailstock. You can swap ends for good finishing.
With the weight finished, I once again set it on the little balance scale to compare it with the tin can full of shot. There was little difference between the new weight and the temporary weight, as planned.
Since there is a hole in the center of the weight, the weight cord must be doubled, with a strand on either side of the rod through the hole in the weight. The ends of the cord are tied into holes in the winding drum, which also has a groove in its center to pass the 3/32" weight track rod.
The weight is suspended from cords in a plate which is screwed to the spigot in the top of the weight. The cord passes through two small holes in the plate and wraps around the spigot. This arrangement allows the cord to slip a little when the weight is suspended to equalize the weight on the two strands of the chord.
The weight plate is made from .030" shim stock steel and blued to make it handsome.
Today's links:
Top
Top and tube
Shot and shell
Equals
Pressing on top
Top pressed on
Lead in shell
Lead machined
Drilling lead
Weight plate
Final weigh
Weight finished
Weight and can
Assembly mounted