When I heard that MEWS was about to republish the Sun Clock it seemed a good time to update readers on recent developments.
In February, 2012, the Austrian Sundial Society contacted me and said that they were planning to install a version of the Sun Clock in the grounds of Schwarzenau Chateau, Lower Austria. Naturally, I was pleased, but concerned that the Sun Clock, in its published form, was not suitable for public use. In fact, as I said in the MEWS article, my original sundial was just a concept model. So, here is Mk2, which includes the following improvements:
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•Better weather protection
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•Increased strength
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•Improved vandal resistance
Of course, it is impossible to totally guarantee against the ravages of the weather and man without encasing in 'bullet-proof glass', so the Mk2 remains a compromise.
In the description of changes that follow, the part names and drawing numbers are those of the original sundial (photo above and GA drawing in Part one), and the drawing numbers described below refer to those on the General Arrangement Drawing – Sun Clock MK2 (above). Click on these drawings to enlarge.
The drawing shows the Sun Clock set to the latitude of Schwarzenau, but it is a simple matter of tilting the dial to suit other latitudes. This, and other aspects of adjusting the Sun Clock, is fully described in the MEWS article. I suggest stainless steel be considered for most of the parts for improved corrosive resistance and to give it 'the modern look'.
Drawings to which the changes below apply to produce the Mk 2 will appear in the next two parts (we decided to include the changes here so that builders can switch straight away to the new version if they wish.
1 Dial, Drg 40. The thickness is increased from 1.5 to 3mm for increased strength. Letters and numbers are engraved, and the upper surface bead blasted to give a satin finish for good shadow contrast.
2 Winter Dial, Drg 41. Here, I suggest a major change: I have shown the Winter Dial fixed; it also acts as the Dial Support (originally Drg 25). The reason for this is to improve strength and vandal resistance.
Furthermore, the earliest sunrise and latest sunset during the winter in Schwarzenau is 6.34am and 6.50pm. A fixed winter dial can allow coverage of, for example, 6.30am – 6.30pm (12hr apart). In other words, there is only a small part of winter daylight hours when it cannot be used. Also, the sun is weak and is only just above the horizon at the early and late hours, so the shadow will be indistinct. The same argument holds true for other parts of northern Europe including England.
The Winter Dial is welded to the Dial for strength and the welds are hidden in the four slots cut into the Winter Dial. I did not want to have fixing screws on the top surface of the Dial. The original design, with the moveable winter dial, can of course still be used, but that is probably more suitable for use in a private garden or where public access is restricted.
3 Pillar Plate, Drg 9. The thickness is increased from 1.5 – 3mm for increased strength and rigidity.
4 Slotted Plate, Drg 8. The segment angle is increased. This provides coverage of the mechanism from 'inquisitive fingers' (particularly the two springs)!
5 Ring, Drg 4. The thickness is increased from 1.5 – 3mm for increased strength and rigidity.
6 Cap, Drg 11. The 24mm dia is increased to 30mm. This is because of limitations in the sizes of 'security' grub screws available (M5 x 8 long).
7 Skirt. This is the second major change to the design. I have provided the mechanism with a 'Skirt' to give better weather protection and to guard against 'inquisitive fingers'. It does not cover the mechanism completely but, like an umbrella, it might be sufficient. However, the Skirt could include a cover plate if necessary. The Skirt is made from a bent strip of stainless steel with five fixing tabs welded on (7a), and is screwed to the Pillar Plate. The join could be sealed on the inside with a fillet of silicone sealant. Alternatively, it could be welded to the Pillar Plate. However, I am not sure if it should be 'tack' welded or continuously welded (I would be concerned about distortion, but I do not have any experience of that).
8 The size of the two main fixing screws is increased from 6 to 8mm for strength.
9 Radius Boss, Drg 5 and Pivot Shaft, Drg 6. These two parts are combined and machined from solid for strength and concentricity.
10 Support Columns. Machined from solid for increased strength.
11 Adjusting Screw, Drg 17. This is replaced with an 'off the shelf' stainless steel security screw. For example, one from the range: http://www.securityfasteners.net/Pin-Hex/View-all-products.html
The screw is used to make the longitude adjustment and, thereafter, just twice a year for 'summer and winter time' settings. To allow the public to do that would be inviting disaster – the sundial would never indicate the right time!
In fact, all the screws used for the revised design are security screws.
12 The latitude angle of Schwarzenau, 48.73 deg, is secured with location dowels. These are probably not essential, but are intended to prevent slipping due to rough handle by members of the public!
13 Base Pillar, Drg 3. The diameter is increased for extra rigidity more and in order to incorporate the location dowel.
14 Base Plate, Drg 2. This is increased in thickness from 3 to 6mm, again for increased strength and vandal resistance.
15 Gnomon, Drg 45. The original Gnomon was made from Nitinol. The use of this material is essential if the sundial is to be used by the general public. With the design shown it is 'impossible' to permanently bend the Nitinol gnomon. Incidentally, it is also extremely hard and impossible to saw with a high-speed steel saw blade! Nitinol is available from Germany and China, but the cost of a small quantity can be an issue. Needless to say, the protective knob must be fixed on well with 'super glue' and the Gnomon fixed tightly to the sundial!
Finally, in accordance with the Austrian Sundial Society's intentions, I have shown the sundial mounted on a granite boulder – at least that won't go missing!
