ferrite machining?

I worked in an auto machine shop years ago and had to fit huge truck king pins and their steering knuckles together. The final tolerances were less than 5 ten thousandths of an inch. Those bushings had no brittleness. I had a bucket of smashed ones, and they make great shims under a hydraulic press, particularly due to their malleability and softness. More firm than raw brass, but certainly no rough granularity to it like bronze. It was a fine matrix.

I made a simple fixture to hold a Dremel tool on the toolpost of my Jet 9X20 Metal lathe. Most of the 9X20's seem to have the same castings so there are a lot of them around. The cutting tool for this job would be the same as what I use for e-clips on rod stock: the tiny abrasive disk that shatters every time you use one hand held. It will last a while in this application. As for the tool post mount, think about a piece of angle, wood block & wood screws and hose clamps. light cuts don't need to be super rigid. A well positioned vacuum cleaner (use duct tape!) will save a lot on clean up.

John Ferrell W8CCW

The fibrous "concrete saw" type disc works better. "dado" two together for wider cuts.

Only in the sense that the crystal structure that you get at the atomic scale spaces the magnetic nuclei at the right separation from each other to maximise the kind of interaction that you want.

Resin-bonding couples rather larger groups of atoms. It doesn't have any effect on the atom-to-atom spacings that dictate the basic magentic properties of the lumps of ferrite being bonded, but the space taken up by the resin means that there is less room for ferrite.

-- Bill Sloman, Nijmegen

But not enough like ceramics for the comparison to be useful? So why did you bring ceramics into the discussion in the first place?

-- Bill Sloman, Nijmegen

BlindBaby was expressing himself with his usual lack of precision. You've snipped the part of my response that dealt with the other meaning that he might have had in mind - or more likely you didn't bother to read past the point at which you could insert your smart-ass comment, and the snip merely reflects your limited attention span and your deficiencies in the mental faculties usually mobilised in interactions between adults.

Getting excited about typos again?

-- Bill Sloman, Nijmegen

That depends on the level of liquefaction introduced.

I didn't. Someone else did, and they called them ceramic. I corrected him, and then I referenced that here. IF you had enough brains to actually have read the entire thread, you might have caught that.

But I fear that you don't catch much.

Shame, that... smallpox or the like comes to mind.

Talk about PKB.

You haven't even read the thread. The deficiencies are all YOURS.

Sure, but with much finer stuff than I have here, unless I go to wet'n'dry emery paper.

The exercise I tried last night was simply to get a feel for how the stuff reacts to 'hobby' working, and also to see how easy it is to fracture that stuff.

Machining a fine groove is difficult because of the need to keep the tool moving to avoid creating a hot spot that will generate a fracture somewhat like scratching and tapping glass does. The stuff is very brittle but still easy to machine with lots of patience and a light touch.

I've broken many transformer cores trying to recover them from busted PC power supplies -- haven't hit on a safe way to get them apart when the things have so well been vacuum with varnish or glued. One pair from maybe couple dozen attempts, but I wrecked the former -- found a transformer not well varnished that time.

My interest in grinding ferrite stems from seeing an article on a high power transformer where the author ground the centre stem down to half diameter, instead of using a gapped core. I forget now just why this was considered better than an air gap.

So many here prefer arguing instead of simple discovery ;) Suck it and see.

Grant.

Yes, I discovered that last night, localised heating trying to get a narrow cut will easily start a fracture, there's no great pressure or vibration evident to cause the fracture, it's the localised heat. Obvious, when one works with the material. Need to keep the tool moving to distribute the heat loading.

And the generated heat is very localised, I was holding the ferrite in my hand, and the stuff did not warm up after being ground.

Ferrite not a good heat conductor. I've also fractured ferrites by heating with a hot air gun trying to soften the varnish and/or glue to separate and recover transformer parts. same story, localised heat will fracture ferrite material.

Grant.

The 22mm red and black ones? I break them not in use, but in careless handling of the tool! Only had high speed thingy for a few weeks, it's been great.

Yes, I need to arrange some dust vacuum here, but it's more difficult for handheld -- I'm dreaming up some sort of blower + vacuum arrangement that could help direct the dust to a vacuum. Or maybe a high volume, low vacuum fan and duct arrangement so some sort of filter; like I've seen in some photos of handheld machining.

The 150 grit diamond tool tips in the cheapy abrasive sets seem too harsh for ferrite, they jar and shatter, but diamond does cut the stuff quite well. So I imagine finer grit diamond tools would be good to try.

The miniature thin cutting off wheels are much slower cutting ferrite, but very little vibration if you properly mount and dress them before use.

Grant.

Jeweler's rouge from the hobby shop. It's a rock polishing tool. Pot cores are like rocks.

Folks been doin' it that way for decades. Many decades.

If you guys are overheating ferrites, I'd say that your technique suffers from more then tool speed issues.

Even fast rise in an oven will do it, so even full body heat will do it, if the rise rate is too high.

In fact, that is where you have to most watch out for it. Reflow and wave pre-heat profiles.

This is also why a lot of transformers and such which are ferrite based get attached by hand post automatic process.

But dremeling is not going to do it unless you are just plain dumb about it.

A nice, fine set of jeweler's file also cut meat away pretty well. You just have to watch that you are not too aggressive with the stroke speed and pressure. It is, in fact, a very nice way to do some tasks one might find a need for in ferrites. I used a flat file to shave pot core faces pretty often, since the mini pot cores fit onto the whole file flat. Or I would use the file as the base/face for my abrasive paper or cloth.