I wanted to make a sundial which overcame some of the perceived difficulties associated with dials, i.e.:-
a) The need to go outside to read the time.
b) The confusion caused by a 24 hour display, (we are all used to 2 x 12 hours in a day).
c) To be usable when the sun isn't shining (you will find that I cheated with this one)
I decided that the answer was to make a sundial using a two component system, with a collector (in the garden) linked to a remote display unit (in the house), utilising fibre optics.
Fibre optic cables (FOCs) have been used to make sundials before of course (1,2) I make no claim of originality in that respect - though this is the first of this particular design (as far as I know)
The collector (Figure 1) is half a plastic pipe cut lengthways. I used 160mm length by 150mm diameter. The mainproblem was to find a pipe that did not change shape when cut down the middle - I eventually used a pipe used for underground drainage (5mm thickness) which was stable, but I had to try quite a few different types before finding one which was suitable. The ratio of length to diameter was not critical, so long as it would cope with the maximum variation in sun's declination over the year - I allowed plenty of margin.
I also had quite some difficulty getting suitably "low tech" (low cost) FOC - it was easy to find high priced sheathed FOC as used in communications. I eventually managed to get some 1.5mm diameter unsheathed FOC from a theatrical lighting supplier - they use them for making "starry night" backcloths for stage productions. They sold me one of their used "looms" for a nominal charge.
At 1.5mm FOC, the 150mm diam collector, gave enough "space" to have one FOC every 5 minutes without overlap, but I opted for one every 15 minutes for this, my first attempt. I marked out the spacing on paper using vertical lines, then attached the paper to the inside of the half cylinder. The 1.5mm holes were drilled offset vertically to keep them distanced - in Fig 1 you can see that the holes were drilled in groups of 4. This made it easier to identify them later at the assembly stage.
Originally I was considering using a cylindrical lens to focus the sunlight (1), but trials showed this to be an unnecessary complication. In practice, stray light was more of a problem. Hence, the collector was sprayed matt black to keep spurious reflections to a minimum.
My first plan was to cover the face of the collector, leaving a narrow slit down the centre, in order to light up one cable end at a time, rather like Robert Adzema's "Crack of Dawn" dial (3) However, this created a problem,as the width of the light ray varied depending on the time of day. You could, therefore, get times in the early morning and late evening when the ray fell between FOCs and none of them was lit, or get more than one being illuminated around noon. I therefore decided to cover over half the collector as shown (the upper crosspiece is there to give a degree of rigidity and ease of construction) The cover was made from thin, rigid "Formica" type laminate. Thus, as the sun progresses, more and more of the FOCs are illuminated.
The half cylinder collector was mounted equatorially (53 degrees here), and was offset from noon to collect the sun during the 12 hour period 9am to 9pm - see Figure 2. (I no longer have to get up at 6am,so I don't). It was set for
