Mark-1 Prototype

After a trip to the hardware store to get aircraft cable, cable clamps quick-links, screw-eyes and some beam clamps we got to work on the building. Mark's tabletop cradles used small screw-eyes (it's like an eye-bolt only with wood-screw threads instead of machine threads) to mount the billiard balls. Our idea was to simply scale-up his idea and use much larger bolts. Our screw-eyes are 3/8" in diameter as opposed to Mark's original design which used eyes of about 1/16th". The dimension is the OD (Outside Diameter) of the bolt shaft itself, not the ID (Inside Diameter) of the Eye on the end of it as many people mistakenly assume. The eye itself is about 1.25"ID.

First we had to rough cut the cables and make the top-end assemblies.

We used I-Beam clamps with large eyebolts. This would be the semi-permanent upper fixture that would support the balls. We put a quick link below that for easy removal of the cradle when we needed the room (it takes up a massive amount of floor space when assembled). By leaving the clamps on the rafter beam we can maintain the spacing of the balls (a very tedious and difficult thing to initially establish). Below the quick link is a loop of cable and a pair of clamps. By putting the quick link in there it also has the advantage of making the hinge-point between the eyebolt and the quick link instead of the upper loop of cable. The links and bolts are much stronger and tougher as well as cheap and easily replaced. This increases the safety of the system a great deal and makes the maintenance of the cradle far cheaper. Because it's a direct friction point with two pieces of metal rubbing against each other it will eventually wear through. It's much easier to just change out the eyebolts and quick links than to have to replace all of the cables (aircraft cable is very pricey).

We nicknamed the guy in the red shirt "Counterweight", he is their leader.

After making the top ends we had to make the bottom ends. We needed to find a simple way to ensure that all of the cables were the exact same length. Usually this would be done with turnbuckles, but having the mass (and subsequent inertia and self-resonance) of turnbuckles on each cable in this application would be unacceptable. We thought of assembling a focus group of genetically enhanced super-genius research scientist ninjas but budgetary restrictions forced us to limit our options so we found a few weirdo's hanging around the lab with a folding chair and a piece of scrap conduit.

After rough-cutting the cables and making the top-end assemblies the fearless Andrew Jager spent an hour up on top of our big stepladder mounting the I-Beam clamps to the rafters. The rafters we chose was the best compromise between height off the floor and angular separation of the support cables. We wanted the cradle to have the highest rafters possible (which would be the center ones), but we also needed to have them as far apart as possible to maintain the alignment of the cradle (too close and the balls will twist).

Now we had to mount the balls. This was the point when we learned that like most other forms of sporting equipment balls, Bowling balls are NOT homogeneous. They have a colorful hard candy shell and a comparatively gooey inside. Old (like 70's vintage) bowling balls are often filled with rubber. Drilling a hole with a cordless hand drill into a hard smooth sphere held between your legs (because it will NOT fit in the vise on the mill) is an exercise in patience, pain, and required the invention of several all new swear words. Add to this the fact that it STINKS LIKE MAD and you can guess just how fun this was. The stench of this process was considerable and was by far the worst part of the project. After a couple hours we managed to get all the balls drilled and the screw-eyes installed. Because the photographer was called into service to help we didn't manage to get any pictures of this. Thankfully we managed to complete it without anyone bleeding.


The initial test weights. It became instantly apparent that all of the balls would require two eye-screws. We had to give this a shot just to see though.


After another round with the joy of drilling, Andrew and his unidentified friend mounted the balls to the support cables.


At the end of the day we had our finished working prototype of seven mismatched balls. The balls ranged wildly in age over a 30 year or more span, and were radically different in weight and construction as well. Despite all of this, though it worked poorly, the cradle DID work and proved that if we built a real one it would be an excellent new demonstration piece for the lab. It was clunky and ugly, but a perfect proof of concept for the final design.