The magnets I ordered for testing arrived and I've completed testing them. I was surprised by what I found out!
Dave Bell, who knows about these things, warned me that I might have problems with my original magnetic gnomon (design 1). He was correct. If you recall, my first design used two magnets- a large disk magnet in the stained glass, and a smaller mounting magnet placed in the center of the larger disk magnet. Dave said that they would not work well together because the larger disk would repell the mounting magnet. This is exactly what happened! He said that a better solution would be a steel disk in the stained glass, with the mounting magnet attached to it in the center. This way, you avoid the wierd repulsive forces that occur when two different sized magnets are placed together. Only two disk magnets of the same diameter will stick well together. A small disk magnet will not sit well in the center of a big disk magnet. Using one magnet with a steel disk works much better than two magnets. These magnets are strong! I ordered and tested larger mounting magnets, but even the larger 3/8" mounting magnet was too strong. The tiny 10mm (.39 in) mounting magnet worked best for the small 5 inch long gnomon I will be using. A bigger heavier gnomon might require a larger magnet. Another interesting thing I learned during testing is this- I placed the mounting magnet (with gnomon rod attached) on the steel diak and simulated bumping into it. I found out that I could tilt the gnomon by about 45 degrees and then it would snap back into place if I let go. This is neat! It means that someone could bump into it and it would relieve the impact by tilting. Then it self corrects. If someone hit it reallyl hard and it tilts more than 45 degrees, then it will fall off. Cool! Here is a drawing of the new design: http://www.flickr.com/photos/jlcarmichael/5351974782/ My design 2 is not the only magnetic configuration that would work on a stained glass sundial. Another way of attaching the gnomon would be to have a disk magnet against the glass on the inside and an identical disk magnet or a steel disk (with a gnomon attached) on the outside, with the stained glass sandwitched in between. Or, you could place a disk magnet on the inside of the glass and place a steel gnomon on the outside. All of these will work. Note: Do not use stainless steel! Magnets don't attract it. John From: Dave Bell [mailto:[email protected]] Sent: Sunday, January 09, 2011 12:45 PM To: 'John Carmichael' Subject: RE: Magnetic Gnomon (design 1) That would work perfectly, and look great, too. The plated steel disk could of course be any size you cared to make it, larger than the cup. Using the brass washer is a perfect solution to keeping the gnomon centered. It would work just as well for a classical polar gnomon, with two magnetic "feet". Another benefit: Magnets don't like high heat. I would be a little concerned about soldering came around a NdFeB disk. The plated steel wouldn't be affected at all. _____ From: John Carmichael [mailto:[email protected]] Sent: Sunday, January 09, 2011 11:28 AM To: 'Dave Bell' Subject: RE: Magnetic Gnomon (design 1) Hi Dave: I hadn't thought about that! Magnets are so wierd. That's why I need to test them first. I like your idea. I could even gold-plate a steel disk so that it is pretty and would look like a gold sun in my design. And the gold plating would keep it from rusting too. The steel disk would be on the inside, and the brass disk with the hole would be on the outside. I can't wait for my magnets to arrive so I can begin testing them! I'll let everyone know the results. Thx! John From: Dave Bell [mailto:[email protected]] Sent: Sunday, January 09, 2011 11:22 AM To: 'John Carmichael' Subject: RE: Magnetic Gnomon (design 1) Looks great, John! The only suggestion I'd make is to just use a steel disk, like a plated washer, perhaps, instead ot the disk magnet in the window. You probably don't need the extra force of the two magnets working together, and you may have a problem getting them actually to work together. The Mounting Magnet is arranged with the poles on opposing faces of the embedded disk magnet. One pole is thus exposed in the center. The opposing pole faces into the steel cup. The field lines of that pole are led through the cup, and out to the edge, next to the inner magnet. All the attractive forces are in a narrow torus surrounding the gap between the inner disk and the rim of the cup. These work great against a plain steel surface. The disk magnet you are suggesting for the window would probably also have its poles on opposing faces. One pole would cover the entire outer face. This pole would repel either the center disk of the Mounting Magnet, or the rim. Dave _____ From: [email protected] [mailto:[email protected]] On Behalf Of John Carmichael Sent: Saturday, January 08, 2011 9:57 PM To: 'Sundial List' Subject: Magnetic Gnomon (design 1) Since a picture is worth a thousand words, here is a drawing of my magnetic gnomon design that I hope to use on the new stained glass window. To avoid glass cracking and breakage from an impact, the gnomon is held onto the sundial face with two magnets. One magnet is a round 1/16" thick, 1" diameter disk located in the stained glass window. It is held in place in the by soldered lead came. See: www.kjmagnetics.com/proddetail.asp?prod=DX01 Next to it is an identical brass disk with a hole in it. A small 10mm wide mounting magnet sits in the hole. The hole in the brass disk keeps the mounting magnet from sliding around. It is also held in place by the lead came. See: www.kjmagnetics.com/proddetail.asp?prod=MM-D-10 A threaded brass rod gnomon is screwed into the mounting magnet. If something bumps into the gnomon, it will fall off and the glass and the gnomon won't get damaged. Installation is simple, and no nuts and bolts are required! I am conducting tests on this design for possible use on the stained glass sundial that I'm making. See: http://www.flickr.com/photos/jlcarmichael/5338306840/ Note: The actual gnomon will have a brass frog soldered to the brass rod. But I left this out of the drawing to keep it simple. John L. Carmichael Sundial Sculptures 925 E. Foothills Dr. Tucson AZ 85718-4716 USA Tel: 520-6961709 Email: <mailto:[email protected]> [email protected] My Websites: (business) Sundial Sculptures: http://www.sundialsculptures.com <http://www.sundialsculptures.com/> (educational) Chinook Trail Sundial: http://advanceassociates.com/Sundials/COSprings/ (educational) Earth & Sky Equatorial Sundial: http://advanceassociates.com/Sundials/Earth-Sky_Dial/ (educational) My Painted Wall Sundial: http://www.advanceassociates.com/WallDial (educational) Painted Wall Sundials: http://advanceassociates.com/WallDial/PWS_Home.html (educational) Stained Glass Sundials: http://www.stainedglasssundials.com <http://www.stainedglasssundials.com/> (educational) Sundial Cupolas, Towers & Turrets: http://StainedGlassSundials.com/CupolaSundial/index.html
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