Magnetite cores?

[Paul-R]

Well,  i am in the process of making my first magnet pulse motor ... Bedini style cores, but im not satisfied with them because my rods are about 3 mm in diameter and i cant find any better here where i live.

It is material that counts, although he diameter is important. John B recommends R45 or R60 gas welding rods. They can be obtained from people like British Oxygen and others. They take on magnetism rapidly and shed it rapidly.

[sm0ky2]

ideally you want semiconductor-grade ceramic-ferrite inductors
you can buy these in all shapes, sizes and parameters
or reuse them from old electronics.
(don't use the rubber pegs, they burn tons of energy!)

However, if you want to make your own....

there are mechanical crushing tools, most are noisy, messy and cause heavy losses in material..
I prefer to use a mortar and pestle of a very hard stone. crush the magnetite (obtainable from sand with a magnet)
into a fine powder
(in theory yes, finer the powder the faster the response time, i.e. frequency)
and mix with a two-part epoxy resin, and cast into a mold

you can cut, file, sand this down after it hardens to perfect the shape

now: the amount of the powder you mix into the resin will determine the inductance of the core.
and there IS a maximum that the resin will hold, before it just hardens into crumbs.....

hope this helps, I gave up making them a long time ago, the computer guys are much better at fabricating these things

[antimony]

ideally you want semiconductor-grade ceramic-ferrite inductors
you can buy these in all shapes, sizes and parameters
or reuse them from old electronics.
(don't use the rubber pegs, they burn tons of energy!)

However, if you want to make your own....

there are mechanical crushing tools, most are noisy, messy and cause heavy losses in material..
I prefer to use a mortar and pestle of a very hard stone. crush the magnetite (obtainable from sand with a magnet)
into a fine powder
(in theory yes, finer the powder the faster the response time, i.e. frequency)
and mix with a two-part epoxy resin, and cast into a mold

you can cut, file, sand this down after it hardens to perfect the shape

now: the amount of the powder you mix into the resin will determine the inductance of the core.
and there IS a maximum that the resin will hold, before it just hardens into crumbs.....

hope this helps, I gave up making them a long time ago, the computer guys are much better at fabricating these things

Your post helped a whole lot actually.  You adressed aspects of these cores that i havent thought of before.

I was thinking about getting a smaller amount of magnetite, and experiment a little bit with. 
Do you think that you can substitute the casting epoxy with glue,  or something else?

Thanks m8

[sm0ky2]

Your post helped a whole lot actually.  You adressed aspects of these cores that i havent thought of before.

I was thinking about getting a smaller amount of magnetite, and experiment a little bit with. 
Do you think that you can substitute the casting epoxy with glue,  or something else?

Thanks m8

sure, the medium can be anything that's not electrically conductive, and non-ferrous.
you could use playdough if you want to,.. however
in practice, the harder the substrate (like in a ceramic inductor), the faster the response time, and lower reluctance to induction.
also, if the substrate is too soft, particles can migrate or cluster over time, resulting in changes in the induced field.