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"Marble Coaster" is a Rolling Ball Sculpture. It is great fun to see one in a public place, because they attract quite a crowd at times. Some people will remain for extended periods to try to see everything that is happening. This one is in the waiting room of my dental office, and attracts more than just my patients to come see it. It did some time at the Solano County Fair (Best of Show) and the California State Fair (First Award of Excellence, and Creativity Trophy).

The marbles are elevated at the back left by a pair of sawtooth-shaped ramps, that boost the marbles up one step at a time. Then 3 mechanical switches channel the marbles onto 4 different tracks. Tracks are made of 1/8 inch steel welding rod, and most of the connections are brazed. The 7 rpm motor delivers a marble every 8+ seconds to the top. A pulley and counterbalance system on the lifting mechanism makes for an easier load on the motor.

click to enlarge

 

 One of the most popular features is the "bounce". A marble circles around at the upper left, drops onto a purple pad (toward the bottom on the left), and bounces into the air and then lands in a basket (circle near the bottom of the sawtooth elevator). The purple pad is a slice of a superball on a steel disk, the disk can be aimed by three setscrews underneath, which can direct the path of the ball after it bounces. See the details on the construction page.

This is a great effect, but it relies on the sphericity of the marble for an accurate bounce. Glass marbles are not all accurately spherical, so less than half of available marbles bounce reliably enough to serve the purpose.

Another element is a vertical tube, with pieces of 1/4" copper tubing protruding all around it on pivot axles made of 1/16" brass rod. As the marble travels down the tube, it hits the copper tubes and makes them tilt upwards in a spiral pattern, making noise and visual action as the marble falls through it all. It is seen on the upper right of the top picture.

 Here the marble loads into the top of a pendulum, the arm of the pendulum angles back until the counterweight slows it to a stop. Then it accelerates back up until at the top the marble is dumped onto another track to continue its journey down. The marbles need to be within a narrow range of weight for this to have the right effect. The counterbalance weight can be adjusted for different weight marbles. It needs to be set for the heaviest marble, so that it will return to the top. For the heaviest marble the pendulum travels way out to almost horizontal, takes its time doing so, and looks cool. If there are marbles present that are much lighter, the pendulum only goes a little ways, does it quickly, and doesn't look as good. Between the bounce and the pendulum, I could only use about one out of eight marbles. At 25 cents a marble, I think it is worth it for these effects!

 

 In addition to the elements mentioned above, other elements include a spiral, chimes, spinning rods, a loop, and a bell. The bell is actually a hole saw cutter, which is made of a steel alloy that rings very well. The chimes were from wind chimes.

It is quite a challenge at times to bank the tracks so that the marbles don't fly off the track. I occasionally had to resort to a 3rd rail to insure that the marble stays on on some fast curves.

Construction Details:

The tracks are made of 1/8" steel welding rod. For the most part, I bent it all free hand and by eyeball, but a tool that I found very useful was the wire bending jig available from Micro-Mark. After the whole thing was made, I spray painted it all the background color, and then hand-painted the tracks in a brighter color. The oil-based enamel seems to hold up very well to the test of time and rolling marbles. Others have found 1/8" stainless steel rod is a good material to use with a MIG welder, but between needing the welder and the difficulty in getting an easy source of stainless rod, I think the brazed steel welding rod is a great way to go, and the painted tracks look very nice.

The pieces of track are held in place temporarily by jigs that hold the track spacing and also hold curved cross-pieces. The connections are made with brazing using an oxy-acetylene torch. When I run out of a piece of rod, I braze on a new piece of rod end-to-end. An extremely useful tool for this brazing is the "gas-saver". I got mine at McMaster-Carr Supply. It consists of a hook that you hang the torch from, and the weight of the torch shuts off some valves to the gases. There is a tiny pilot light to light the flame. This way, the settings for the gas levels on the torch are untouched. All you do is pick up the torch, pass it over the pilot flame, and the torch is ready to go with the flame perfectly adjusted. When you are done, hang it on the hook and the gas goes off. It is often necessary to braze only one or two places, and then re-position clamps before more connections can be brazed. The gas-saver saves so much time in setting the torch, and for RBS construction I think it is essential.

Marbles can be found in many different colors at Little Works of Art Marbles. I used one inch marbles. Marbles with patterns of colors look great as they roll on the tracks, as you can see the colors flashing faster as the marbles roll faster.

Want to know more about rolling ball sculptures? When I made Marble Coaster, I had only seen some gumball machines and one other RBS, and had no idea how big this is. I hear that some of the more complex gumball machines can make over $1,000 a month in a busy location, 25 cents at a time. RBS's are fun to watch, and they are even more fun to make.

Check out Eddie's Mind for some imaginative work. He includes some very interesting elements in his work, and seems to be a master of keeping the balls on just two track wires by banking his tracks so well.

There is a forum just for the discussion of these machines at http://groups.yahoo.com/group/rollingballsculptures/

The Rolling Ball Web has lots of information and links about RBS's.

George Rhoads is an accomplished professional at this. He has made many giant RBS's, often using pool balls. I have seen his big one at the San Jose Tech Museum, two stories tall and it is awesome.

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