Re: Gnomons and screws
Hi Mike, I've had responses that indicate that Melville used a variety of methods to attach gnomons, from leading them in, fitting them with flanges underneath to the twisted tenons that you mentioned. No 2BA screws, though! So I am convinced that the ones on the Dunmore (Ireland) dial are replacements. If you have a picture of the actual shape of an authentic Melville gnomon, that would be useful - thanks for offering. (I have the one of the Salisbury dial that Nick Nicholls published in 1995). Otherwise, we will just re-fit the existing replacements which are acually quite reasonable. Regards, John -- Dr J R Davis Flowton Dials N52d 08m: E1d 05m -
Re: Gnomons and screws
In 1884 the British Association for the Advancement of Science adopted a thread form and series, primarily for use in precision equipment. It was inspired by one used in the Swiss watch and clock industry, and was formerly sometimes called the Swiss Small Screw Thread System; but is now just referred to as the BA series. Like the Whitworth thread, it has a rounded root and crest, but the included angle is 47.5ƒ and the radius is 0.1818Ö times the pitch. Brian Albinson -
Gnomons and screws
Dear dialling colleagues, I'm helping to restore a Richard Melville (worked 1832-1871) slate dial with multiple gnomons. The gnomons are held in with 2BA brass screws using square nuts. The gnomons themselves are nominally 1/4 inch thick but with considerable variation, i.e. not the modern rolled plate accuracy. Can anyone tell me when the BA (British Association) screwthread standard started? I think it points to the gnomons being (old) replacements. Regards, John Davis - Dr J R Davis Flowton Dials N52d 08m: E1d 05m -
Re: Gnomons and screws
Dear John, I believe that Melvillemade his gnomons such that they have two tangs that poke through the slate. These are then each bent in opposite directions. I am sure that he would not have used screws. I can send you photographs if that helps. Regards,Mike CowhamCambridge UK I'm helping to restore a Richard Melville (worked 1832-1871) slate dial with multiple gnomons. The gnomons are held in with 2BA brass screws using square nuts. The gnomons themselves are nominally 1/4 inch thick but with considerable variation, i.e. not the modern rolled plate accuracy.Can anyone tell me when the BA (British Association) screwthread standard started? I think it points to the gnomons being (old) replacements.
Gnomons and screws
Message text written by INTERNET:sundial@rrz.uni-koeln.de I'm helping to restore a Richard Melville (worked 1832-1871) slate dial with multiple gnomons. The gnomons are held in with 2BA brass screws using square nuts. The gnomons themselves are nominally 1/4 inch thick Can anyone tell me when the BA (British Association) screwthread standard started? I think it points to the gnomons being (old) replacements. John if you go to http://www.bhi.co.uk/hints/bathrd.htm There's a history which starts: Way back in the 1890's, the British Association for Advancement of Science (BA) realised there were no English screw threads standards for small electrical and scientific equipment, so they proposed the BA system loosely based on the Thury threads already in use in Europe (hence the metric sizes). They quickly caught on and rapidly became the standard in the UK. They are good news - thread angle of 47-1/2 degrees (good for holding in thin work like clock wheels); rounded tips and crests (less power needed to cut, less risk of tearing threads, less wear on the tools); enormous range of sizes (0 - 26BA). I think you are right - the slate Melville dials I have seen all have their gnomons set in lead. Though it's possible the centre (main) ones might have some further support underneath. Patrick -
