More good questions Frank. You're giviing me some good ideas for talking points in my article.
Answers below: -----Original Message----- From: Frank King [mailto:[email protected]] Sent: Monday, May 16, 2011 2:22 AM To: John Carmichael Cc: 'Frank King'; 'Sundial List'; [email protected] Subject: Re: New Monumental Sundial in Oro Valley Dear John, Many thanks for the follow-up. I now have a heap more questions!! In your drawing you have half-hour dots and quarter-hour tick-marks. In the photographs, I can't see the tick-marks. Is that my poor eyesight or did these get lost as a budget-saving measure? Answer: The project coordinator removed the ¼ hour marks because he wanted the dial to look simple and easy-to-read. I did not agree with this decision, but I was overruled. See: http://www.flickr.com/photos/jlcarmichael/5717421627/sizes/o/in/photostream/ Also in the drawing, you have the tick-marks aligned with the root of the gnomon but the hour-labels are aligned with the centre of the ring. Did you consider having the hour-labels aligned with the root of the gnomon? I wonder what the shadow looks like at 10:15am, say, when it strikes through the number 10 at an intriguing angle? Answer: Great question! I do this with all my dials. I think you guessed the answer already. The shadow time marks are used for telling the time, not the shadow on the numerals- obviously. Like you, I consider the numerals to be just labels for the time marks, so these labels should be directly centered in front of the hour marks. This is why I did not align the hour numerals with the gnomon root. This whole dial looks like a seriously tempting object to climb up! Did you do stiffness calculations on the gnomon to check whether someone could swing on it? Answer: Gnomon stiffness was a big concern for us. If you recall we discussed this issue in detail on the Sundial List many months ago. We worried about gravity bending the gnomon. We determined that a hollow tube was stronger than a solid rod. We were not concerned with kids hanging on it because its lower tip is 7 feet off the ground, above the reach of kids. Adults can touch the tip. I pulled down on the tip and I could not get it to bend at all. Is the point where the gnomon meets its support in the same plane as the dial plate? Answer: No! This is what made the design so difficult. The attachment point of the gnomon to the gnomon support tube is about 8 inches behind the face of the dial plate! As a theoretical exercise, marking out a dial that declines 45 degrees and is offset from the vertical 12 degrees is not a big deal for most readers of this list but... Actually fabricating the dial, gnomon-support and gnomon itself and then assembling these components with the correct orientation looks like a very big deal indeed! Answer: Without fancy 3D computers it would have been nearly impossible! It drove us all crazy. I draw in 2D using Delta CAD. The engineers at CAID Industries had to make the highly 3D sculpture conform exactly to my drawings and specifications and the artists models. I based my drawings on a cardboard mockup done by the sculpture artist, Jon Seeman. His model had to be redrawn in 3D on CAIDs computer. I should be interested to hear just what jigs and tools were used and what checks were made at the fabrication stage to ensure that all the components were correctly aligned. What metrology procedures were used? like a very big deal indeed! Answer: I wasnt present at the factory for the fabrication, but below youll see a photo of Phil the welder. During the dial testing and gnomon attachment session at the factory, I was amazed to see the jig that the welder used to align the gnomon with the gnomon support tube. See these photos! http://www.flickr.com/photos/jlcarmichael/5726242657/in/photostream http://www.flickr.com/photos/jlcarmichael/5726241005/in/photostream http://www.flickr.com/photos/jlcarmichael/5715931783/in/photostream Do you have secret levelling screws and so on to make minor adjustments when installing the instrument on site? Answer: Amazingly, no. No leveling screws were needed since the cement foundation and the sculpture were so precisely designed and constructed. When we installed it, the crane operator and the men on the ground simply had to align the bolt holes in the flat base of the dial with the bolts in the foundation. No doubt your article will give us some gory details! All the best Frank
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