Hi John, For holding strength through a thick piece of glass you would need a magnet that had such a strong field over that gap. The Rare Earth magnets, although extremely strong at short distances have a field that falls off quickly with distance. Two long flat bar Alnico magnets, on inside and the other embedded in the gnomon would probably work better. Rare Earth magnets embedded in 400 series Stainless Steel might work ( + at one end, - at the other), since the steel would function as a magnetic shunt, increasing the gap strength. I don't know about plating the Rare Earth magnets, but Alnico can be plated. You might still want to have some silicone or polyurethane in the sandwich to protect the glass. Someone might like to go through the magnetic equations to optimise the structure against extreme wind conditions, etc.
Hope this helps! Edley McKnight Ancient in Oregon. From: "John Carmichael" <[EMAIL PROTECTED]> To: "Sundial List" <[email protected]> Subject: Magnetic Gnomon Attachment Date sent: Tue, 1 Feb 2005 11:30:13 -0700 Send reply to: "John Carmichael" <[EMAIL PROTECTED]> Hello All: Two weeks ago, I attached the gnomon to my bay window stained glass sundial.In the original prototype, I had used a brass baseplate adhered to the outer protectiveglass with silicone. But this baseplate was a little ugly becauseyou could see itbehind thepainted sunnface piece in the sg panel.So instead,Iepoxied therod & sheet gnomon to a 3" square piece of clear glass and then siliconed it to the outer protective pane. The edges ofthe baseplateline up with the lead came sothe baseplate isinvisible from inside the room. (you can see new photos on the SGS website). Anyway, I've been thinking that for some future project, that it would be possible to attach the gnomon to the SGS using a magnet. If a piece of stainless steel were in the stained glass design, and if the gnomon baseplate were a magnet (or vias versa), then you could secure the gnomon to the SGS without fear that it could crack the glass. If somebody bumped into the gnomon, it would simply fall off, avoiding any damage to the glass. If you have a double-paned window, you could glue the magnet to the inside or outside of the outer protective pane. Nobody has used this method, but I think it might work. (you could do the samefor atable-top analemmatic to keep the gnomon in place during high winds). John John L. Carmichael Sundial Sculptures 925 E. Foothills Dr. Tucson AZ 85718-4716 USA Tel: 520-6961709 Email: [EMAIL PROTECTED] Websites: Sundial Sculptures: http://www.sundialsculptures.com Stained Glass Sundials: http://www.stainedglasssundials.com -
