Machining Neodymium Magnets

After-market machining neodymium magnets.

Amazing Magnets does not generally recommend machining “live” fully charged magnets as they are brittle, sensitive to temperature, and generate magnetic powder which makes the operation tedious and messy.
 

Important Warnings:

Heat will demagnetize a magnet. Magnets have a maximum operating temperature and will permanently lose their magnetism when heated above that temperature. Usually, this is 176F/80C but depends on the exact material in question. Temperature specs can be found on the information page of the part. Low speed, soft pressure, and constant temperature checks should be used to avoid overheating or cracking the magnet during machining.

Magnet Powder

Neodymium magnets are composed of sintered metals which are essentially compressed powder that turns back into dust when ground, drilled or cut. Because the powder is magnetic, it sticks to the drill bit and magnet and can’t be easily removed. The best method is to move as much powder as you can to the edge of the magnet and pinch it with your thumb and index finger. Blue painter’s tape can be used to clean the remaining powder.

Rust / Oxidization
Most neodymium magnets are coated/plated with nickel or zinc to protect the substrate from oxidizing(rusting). Neodymium magnets are about 70% iron and will rust quickly when exposed to air. Magnets become less magnetic and more brittle as they rust. We suggest re-coating the exposed neodymium with some type of permanent coating.

We have had success with 2 part epoxy like JB weld. It will seep into the pores of the sintered material and is not easily scraped off.
 

Drilling Holes
Glass cutting or masonry drill bits work best. The higher-end “diamond burr bits” also work, the cheap ones found in your generic Dremel kit do not. It is important to have a bit that can break through the hard nickel coating of the magnets, as well as slowly and carefully remove the sintered magnet material.