Thread: Having A Ball With Volcanoes

G'day mates. WOW! What a response! Your kind assessments exceed my wildest dreams. Thanks for all.

Hmmm. Why indeed? Mostly to convince myself I could do it. But for the past 30-40 years I've had an abiding interest in "mathematical sculptures," starting with Martin Gardner's Recreational Mathematics columns in Scientific American (Google for many of his books still in print). Currently, there's a web site named something like "Geometry Junkyard" with megatonnes of ideas.

The sanding wasn't all that scary. In pic 5 of the second post, note that my left hand is on the toolrest with all but the left index finger in safe territority. My right arm is resting on the tailstock. I pressed ever so slightly on the back of the sandpaper, and dithered the sandpaper under it to reduce extra scratches - worked a little like a belt sander. Yeah, I got bumped a few times, but nothing serious. And as I said, I improvised the tool for sanding the hole interiors. Also note that I re-mounted the piece for each operation in the pix - never sanded the whole thing at once. BTW, the latches were quite the brainstorm; if I had to do it with threaded rods I would have abandoned the project.

So, how long did it take? I didn't keep precise records. I turned the blanks (the magnolia and the podocarpus) in late October '07. By 4 November, I'd turned the spheres and drilled both, and completed the magnolia practise piece (hollowed only three holes - the imbalance was too severe to proceed further). I reckon I had about 12 hours invested by then. Between then and late January '08, I modified the donut chuck and built the steady rest. The steady rest is general purpose, so that shouldn't count. I reconstructed the time line between 27 Jan '08 and 3 Feb (USEST times and dates) by examining my diary and the dates of some more WIP pix. Looks like about 24 hours for that interval; the finishing was only a few minutes every half-hour or so - the rotisserie did the rest of the work. All told, about 40 hours I guess, although I've probably underestimated.

Some details I omitted: The thickness is about 1/4 inch (6mm). The layout itself was a bit of an adventure. There are formulas relating the centre distances to the radius of the circumscribed sphere, for all sorts of polyhedra. Basically, you select a starting point, and swing arcs to create a triangular array on the surface. With luck, the final swings will land at a single spot on the far side - Nope; ain't gonna happen; so you fudge some of the points as needed. Try laying out a large triangular array with compass alone on flatwork if you believe otherwise. A few more oopses came from breakouts. On the hollowing work, there was a faint amount of wobble and I allowed the shank to touch the back side of the hole. Luckily, the breakouts were in one piece each and they weren't too hard to find for gluing back in. Example pic attached.

Thanks again for your generous comments. Now to turn a few Q&D weed pots for therapy.

Joe