John Carmichael contributed: SNIP > >Have you ever tried to squeeze one minute timelines onto an eight inch dial >face? It's almost impossible. Tony and I had this discussion awhile back, >and wondered what was the smallest diameter dial face possible to make that >would have one minute timelines? We concluded that this depends on the dial >face material, engraving (or painting) process and tools used (line width). > >If I remember correctly, Tony said that his fine photoetching process could >just barely do this on an eight inch (20 cm) bronze face. But with my carved >stone sundials, I must have at least a 40 inch (100) cm face for one minute >lines because if carve lines too close together, it weakens the stone. (and >doesn't look good) >
With the photoetching process I use for sundials I've settled on a line width of 0.35mm. The technology will allow much finer lines to be achieved but at the expense of depth, very long etching times or missed bits which then have to be engraved by hand. A line depth of 1/2mm doesn't sound much but is likely to survive weathering for centuries I believe so that is my standard. Assuming that the minimum metal in between lines is equal to line thickness, although I would recommend more than that for durability, elementary trig' will determine the minimum line length for 1 minute spacing at any latitude. Dial shape and chosen position for the 6am/6pm must also be considered as these determine the length of the shortest lines e.g. a long elliptical shape reduces the clustering around noon. Hoping this helps Tony Moss
