ferrite machining?

Grinding is the way to go. If you want to cut something that you would normally do with a lathe in metal, consider a tool post mounted grinder. Watch the temperature rise.

Maybe a dremel with a diamond wheel?

John

After the grooves get ground (any cutting attempt will result in fracture), you need to cover the rod with transformer tape to insulate it from your primary wire.

If you make an open ended core transformer, it will be pretty leaky unless you use a closed loop core arrangement.

You would probably be better off with a pot core.

I would use a dremel tool and grinding or cutting (abrasive cutting) disc attached.

If you are making a large groove for a single layer of larger wire the grooves will allow the wire profile to sit a bit lower.,

If you are using fairly small primary wire, you do not need the grooves at all.

Temperature rise? They are not magnets. There are no properties to lose via introduction of heat.

Here's a tiny pickup coil we wound in a slot that we turned into a delrin rod.

ftp://jjlarkin.lmi.net/BrassThing.jpg

This was snooping eddy current fields inside a superconductive magnet. The n*A is tiny, so we got nanovolt signals. And we had to integrate the voltage to get field intensity.

John

Ferrite is pretty much like ceramic, so you're talking grinding, preferably with diamond

Pretty small wire. Looks like #43 or even a 50 series size. Very fine size.

No shit? Isn't that how all of us would have to do it?

Was it easy to calibrate the circuit output to give accurate readings or was it a little mushy at the low end?

Instead of a slot, I would have wound it, locked the winding with epoxy or other suitable material, and then I would have knocked that little 'hat' off the top of it, making it less of a complete flux path at the bobbin level. The open ended coil would then 'accept' the flux inside the reading area better. Kind of follows as to the same reason that a toroid would be a bad choice for this. You actually want an open magnetic path on this as opposed to normal coil making paradigms where one want to reduce leakage to a minimum.

with diamond

Yep. Not nearly as hard as ceramics are. Not even as hard as your kitchenware actually. Fairly crumbly even, by comparison. But yes, grinding is the only way to remove media from these components because any machine tool application may shock the remaining media, causing unseen microfractures (or seen) that damage the operational characteristic of the media. If the rod is the center piece for a closed loop core, then the mating ends have to be kept smooth and should not be touched at all. The coupling at that interface is important.

If it is an open ended transformer that does not have a closed loop core, I cannot see how trying to top out some efficiency by this primary placement even matters. Put it on top of the secondary.

If isolation is the issue, put the primary inside a Teflon tube, if the turns count is low enough.

There certainly is no 'major' efficiency to be gained by tightly mating the primary wire to the core. Especially if it is an open ended core configuration. Or maybe that is why it DOES have to be tight. It is so lossy that he needs it that close. If that is the case, this situation should be using a fully closed loop pot core or C-I core or the like.

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Wrong. Permeability drops with rising temperature, and leakage flux rises. Ferrite cores don't have to get very hot before they become magnetically insignificant. Read the relevant data sheets for the material used to make your core on the manufactuere's web site.

-- Bill Sloman, Nijmegen

You are wrong. An overheated magnet will lose some of its magnetization level after it cools. An overheated ferrite core will have the same characteristics after it cools.

But getting it hot while grinding it does not hurt it once it cools down, idiot. Nobody said anything about heating it in circuit.

The temp is upwards of 200 to 600F, dipshit.

Again, applying a thermal precaution to a grinding operation is NOT required. The medium remains unchanged after the grinding is completed.

It is the same *when it is at room temp* before grinding, as it is

*when it is at room temp* after severe heating has been introduced from having been ground.

Nobody said a goddamned thing about it being hot during operation or while in use.

Learn to read, dumbfuck.

"No fooling" would have been more appropriate, but for the fetish thing.

Integrator drift was a problem, taking data out to a second or so. We had an analog switch auto-zeroing the thing every shot, and that was barely enough to get good data. Should have ovenized it or something.

The black part is delrin, not ferrite, so it doesn't matter where the slot is located. The greenish thing is a fiberglass tube, nice for routing the wires but not good for machining slots into.

John

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you had me puzzled for a while on how you got a piece of ferrite near a superconduction magnet, or more importantly away from it :)

-Lasse

Oh... so it is 'core free'. In that case, I would have turned the coil on end and encapsulated it into a bead of epoxy. That would make it a component easy to install into/onto any type of 'wand' or whatever device to allow the transducer to be placed into the sampling zone.

As for the fiberglass rod, a slot would be difficult, but a mere cut-to-depth at the end of it is possible, which would let it be able to be used for the windings without the second, Delrin element. The winding wouldn't really need a 'hat' as long as you lock it all down after winding it.

It would seem like a small open ended core of some type would amplify the 'signal' better too. Maybe too much. Cause it to be a little sluggish :-) too.

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True, but not what you said.

Again true, but - again - not what you said.

The managanese-zince ferrites that we use for frequencies up to about a 1MHz have Curie points between 125C and 150C - 260 to 300F. Nickel- zinc ferrites for higher frequency work can have higher Curie temperatures - Philips listed one (good to 50MHz) that had a Curie point above 500C - 900F - though another crapped out at 125C.

150C isn't impossibly hot for some kinds of working circuits. .

Correct.

On the other hand, you didn't phrase your comment to exclude those situations.

Learn to write in a way that doesn't make claims that you didn't intend.

-- Bill Sloman, Nijmegen

This was used to measure NMR gradient field eddy current effects inside a roughly 150 kilogauss magnetic field. Any core would saturate, not to mention mess up what I'm trying to measure.

It would have been nice to have more signal. More turns of finer wire.

John

Diamond rotating saw disk??

--- Unnecessarily nasty when, in all fairness, the thread _is_ about machining ferrite, and the heat he was referring to (which I think most of the rest of us picked up on) could only have been caused by the grinding operation.

--
If frogs had wings?

Pretty easy to grind with normal emery grit products too. Even those 'sut-off-saw' discs will work.

Sjouke Burry wrote in news:4c12c34e$0$14129$ snipped-for-privacy@textnews.kpn.nl:

DAGS for "ferrite machining".

it's a ceramic;grinding can introduce stress fractures(cracks).

--
Jim Yanik
jyanik
at
localnet
dot com