John Carmichael asked: > >What do you think is the best method to attach a metal rod gnomon to a >stained glass sundial window? > >It's the most frequent question I've been getting from the "Glassers". I >do have an article that Mike Cowham sent me that mentions that in the >seventeenth century, a threaded gnomon was usually bolted to a hole cut in >the glass. Of course that resulted in a lot of cracked glass and missing >gnomons, especially if the glass was thin. > I've no practical experience of attaching gnomons to glass but would like to experiment with:
1. modern adhesives to attach a gnomon with a small baseplate. If it drops off after twenty years just clean it up and re-attach. The glues used to stick interior mirrors on car windscreens would be a useful beginning perhaps? 2. attaching through a drilled hole with e.g. a 20mm brass disc on each side of the glass and soft vinyl washers in a sort of 'sandwich' squeezed gently tight with a nut on the inside. The gnomon could be silver soldered to the outer disc before assembly. Twin bolts would prevent rotation. A very safe way to 'drill' glass is to use a short piece of thick-walled copper tube of e.g. 6mm outer diameter with a few radial sawcuts in an electric drill. Garages are a good source of the right stuff. Place the glass flat on a firm/soft supporting surface, e.g. cork, and build a tiny 'dam' around the intended hole site with Plasticene. Mix a little turpentine with carborundum powder, place a few drops within the dam and you can abrade a neat clean hole in no time but reduce the pressure at breakthrough or the hole edges may flake. A thin piece of wood with a 6mm hole will guide the tube until it begins cutting after which it is just gently lifted and replaced to refresh the abrasive. Have fun Tony Moss -
