Date Mon, 24 Jun 2002 101314 EDT
Subject Angle Iron levitation & more Leads
In a message dated 24/06/02, email@example.com writes
Its a deliciously simple design....! I'd think it would be super for a two lead rod levitation unit.
I try to keep things simple! Doesn't always work though!
Its possible the tip of the inverted iron "V", "might" need to be filed down? ....to allow room for levitation... but I could always be wrong.... alot of such angles seem to also be rounded as far as rough hardware type stock. Its also possible for one
to slip in extra iron as a "filler", in case the magnets have too much of a repelling problem. One might need to scan the metal for straightness, before purchasing such. Take care, Meredith
The Magnetic field circuit is from the magnet S pole through the small L angle, then through the main L angle, exiting at the central ridge and then back to the N magnet face. The central point of the main L acts a linear S pole with the return field lines going to the magnet face. This gives a very high intensity field region at and above the central V point. For the field (flux) to be transferred efficiently around the circuit, the L sections need to be of a thickness of ~1/2 the magnet height or more. You will probably get away OK with 1/8" section for a 1/4" magnet, although 1/4" section would be 'safe'. You want as much of the magnetic flux as possible to flow through the Iron Ls. You might find a small improvement if the height of the small L was reduced to just a bit more than the magnet thickness. This could reduce the 'stray' field flowing through the air over the top of the magnet.
The point to understand here is that Iron can carry about twice the magnetic flux that the magnets can give. If you had a precision sharp right angle V and narrowed down the magnet separation, the edge would saturate first and then progressively saturate to a more curved section. However, the tip will still contribute to the overall field. I am not sure how sensitive the lift is to having a dead sharp ridge, but it will fall off if you file a flat of say 3 mm, on the edge. It also falls off if you use too small a magnet separation. This is something that might be determined by a series of experiments with a miniature Hall gaussmeter. Some Hall probes have an active area of several mm square / rectangle and might only give a value averaged over their element size.
The other point is that you are looking for a lift field which not only has a high intensity, but which also has a large rate of field change (or gradient) as you move away from the tip. You require a V formation of (field x gradient) with two main lift 'lobes" (directions) at an angle, so that the graphite rod can rest happily in this V. The force on a diamagnetic rod is proportional to H x dH/dX, where X is the distance from the surface. You would need a very small Hall probe with a micrometer adjustment to be able to measure this gradient successfully, but it could be done.
Now on Pencil Leads.
Faber Castell do produce 1.4 mm Super Polymer leads for their "E Motion Pencils", so I suggest asking for this product and leads for it. They also produce 0.35, 0.5, 0.7 and 0.9 mm Super Polymer leads.
Your information about Staedtler was partially correct. They have dropped polycarbon leads in the 0.9 mm, but still produce them in the 0.5 and 0.7 mm.
Pentel, on the other hand, stock B and 2B leads in the Hi-Polymer version in 0.5, 0.7 and 0.9 mm dia. This would seem like a good source for the smaller leads, since they are a world wide Japanese Company.
I think that I 'have done my bit for the cause' today!
Sorry to hear that John is having problems over the photos. I will try putting them into .jpg format. Not too surprising since the photos were vastly reduced from 3.5 MB bitmap each.... Is anyone else having any problems?