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Unread 31-01-2010, 02:15
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JimS1692 JimS1692 is offline
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Join Date: Jan 2010
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Re: Drilling through a magnet?

Maybe somebody should try the services of an EDM shop.
"Electric Discharge Machining": intense, sharp, repeated sparks (from a custom electrode shaped like the desired hole) erode the hard material, immersed in liquid bath to flush the debris out of the gap and keep the piece and tool cool. As the sparks jump the 3-mil gap and erode the floor of the erosion pit, the tool moves slowly downwards.
The tools tend to be graphite, copper. or tungsten-copper so they erode much slower than the workpiece (probably because they have high thermal conductivity, good toughness, high melting temp, or other things. The piece needs to be conductive. So Neodymium, Samarium, or Alnico would work fine,
but ceramic (aka ferrite) might not be applicable.
Not sure the price, maybe $50-$100, probably too much, but it would probably work OK, and not much does for machining magnets.
Almost all good materials for permanent magnets tend to be especially hard and brittle. There is a reason. The same high density of crystal defects and grain boundaries that keeps magnetic domains from migrating and allowing the locked-in field to relax, also prevent soft deformation of grains and mechanical yielding. It's not quite a law of physics, but is like a rule of basic materials.
Maybe water-jet cutting could work, but it would be slower than most materials. Maybe there should be an acid-jet cutting - most magnetic metals are pretty rustable... an amateur could try putting one drop of CLR or pool acid (hydrochloric acid) in the middle of a magnet disc every so often, then rinsing it, drying it, and putting a drop only in the dimple it made, for some days in a row. Maybe color the top face with a black marker everywhere but the middle, to keep acid wetness from spreading sideways too much.
Just a lot of perspective I thought I could share...