Bouncing a Marble
One popular feature is where a marble leaves the track and drops 25 inches to a pad, bounces 21 inches
high and then lands in the basket. This is like the rescue device: people watching the whole display can’t
wait to see it bounce again, though half the time they get distracted by something else and miss it. Too
many things happening at once is a good thing. It makes a person want to stick around and keep watching.
The bounce pad is made from a slice out of the center of a Superball®. (How to slice a superball here)
The ball is made of some of the bounciest stuff invented by man, and they call it Zectron. Dr. Seuss
couldn’t have picked a better name. I embedded the ball in plaster inside a small wooden box. Brass nails
stick out of the ball in areas that will avoid the path of the saw. The plaster grips the nails, which hold on
to the ball as it is cut. The box, plaster and ball are all cut together into slices with a table saw. When the
pieces are disassembled, a nice 7/16” thick pad of Zectron is what remains.
The pad is mounted on a 1/2” thick disk of steel plate. Thinner steel does not work so well, as the heavy
mass of the steel is needed under the Superball for a good bounce. The steel disk rests on machine screws
that fit loosely into holes in the underside of the disk. These screws can be adjusted to “aim” the plate and
direct the bounced ball into the basket. Another machine screw is threaded into the bottom of the disk to
hold it down. A plastic rim circling the pad is screwed to the steel disk and holds the pad in place, assisted
by epoxy glue.
One of the useful tools for the mechanical parts is a lathe. I used a small and relatively inexpensive Sherline lathe, which did
the job well. One thing the lathe can do is drill a hole into the center of a turning piece. If the work turns and the drill holds
still, the drill automatically wants to go into the center. The lathe can accurately enlarge holes in gears or sprockets to
accommodate a shaft. Bushings can be made to make a large hole fit on a small shaft. Freehand turning of insect parts,
pulleys or the important plumb bob is enjoyable.
Almost everywhere there is a rotating part I used ball bearings. A pulley is made so that the inside diameter of the pulley is
.001” smaller than the outside diameter of the bearing. The two are pressed together, and they stay together. A lathe will
also cut brass tubing precisely, so that spacers and bushings can be made. Several sizes of telescoping brass tubing came
in handy for making everything fit together.
A center drill is perfect for starting holes. It is a tiny, short drill on the end of a much thicker shaft. This keeps the point
from bending to the side, and allows for accurate hole positioning. With a center drill, a drill press and decent eyesight it is
possible to get holes within .006” of where you want them.
The bugs were made of copper and brass. Sheet copper can be worked by annealing: heating it red hot, and then
quenching it in water. It is worked by pounding it with a rubber mallet over a metal or wood form, or a metal hammer
against a plastic or rubber form. As the copper is worked, it gets work hardened. Anneal it again, and then work it some
more. It sometimes takes 8-10 times of annealing and working it to get to the shape you want. Brass is annealed by heating
it red hot, and then allowing it to cool slowly on the bench. When the shaping is done, the piece can be pickled for 5
minutes in a 10% solution of sulfuric acid to remove the oxidation. Fine steel wool gives a nice appearance after that.
Pumice on a wet rag wheel gives another nice finish, and Tripoli metal polish on a dry rag wheel will make it very shiny.
Gold rouge will make it into a mirror finish.
The pieces are soldered using 96/4 tin/silver “silver bearing solder”. It comes from the hardware store in thick wire form. I
pound it flat with a clean hammer against clean steel, and then cut it in half lengthwise with tin snips. Cut it and split it again
until there are pieces 1/4, 1/8, and 1/16 the size of the original wire. The pieces to be soldered are cleaned with fine steel
wool and painted liberally with “LA-CO Regular Soldering Flux Paste”, the stuff plumbers use. After the pieces are
clamped or held into place, the solder is cut into tiny pieces and set right next to the joint to be soldered.
The trick is to heat the pieces to be soldered with a propane torch, without allowing the torch to directly heat the solder or
the flux. The flux burns at only a slightly higher temperature than the solder melts. If the piece is heated too long or too hot,
or the flame spends too much time on the flux then the flux will burn. Heat the work slowly, moving the flame so that
everything heats evenly. Sometimes you touch just the very edge of the side of the flame to the work. When everything is
hot enough, the solder melts and flows right into the joint. If the flux burns and turns brown or black, the solder will never
flow. The only solution is to take it all apart, clean it again and start over. If the flame is too big to heat the pieces without
getting the flame on the joint, then a smaller flame is needed. There are some refillable butane torches that have a very tiny
Heat shielding compound is reusable clay that can hold a soldered part in place while you solder another part right next to
it. It can also be used to hold parts in position for soldering. As it heats up it gets hard, and also keeps too much heat from
getting to the parts that it protects. When done, spray it with some distilled water and put it in a jar, and it can later be used
over and over.