Something along those lines.
Well, I suppose the most important question would be where else can I
ask these questions? Any good forums to recommend?
See, even the definition of lapping is still not clear to me. 3M makes
lapping films I can buy on eBay. What's the relationship to the rouge
the other poster mentionned? Particle size?
I wish to machine some ferrite transformer cores so they can slide
apart but still complete a magnetic circuit when simply pressed
together with light finger-type pressure.
This already exists so it's definitely doable.
However, I wish to do this at home with a minimum of expense.
I figure a 5.25 full height hard disk has the necessary flatness on
the platters for a good lapping surface. I'm not looking for the
ultimate polished finish like a gage block. Just good enough.
I figure putting the lapping film on the platter and making a jog to
hold the work piece steady ought to do it.
I need to know what to do! How to ensure dust doesn't mar the finish.
Textbooks about these processes are quite expensive. Any
I'm going to the library later.
As we get into your need, I think it will be clearer what the
newsgroups might be.
Bonded to the surface.
Should be discoverable, once you have 3M's part number.
Unless you are doing really high frequency stuff, you really do not
need to worry about "jeweler's precision" in fitting this stuff up.
Planning on "interleaving" is a really good idea too.
With hand lapping, you have difficulty maintaining any sort of
parallelism, making the faces smooth is silly if you end up with large
The disk will warp, and you'll have corner gaps. Get a granite
Plenty of water (contraindicated with ferrite materials). Do only one
pass on the "tape". Or simply don't do it.
Recommend magnetics or electomagnetics newsgroups. They might be able
to give you a handle on how-to / if you really need to do this.
David A. Smith
Thanks. I was wondering about the granite cutting slabs you see in
kitchen supply stores. They're all shiny and stuff, but are they
(I don't mean an entire counter top, just a cutting board-sized
I guess there's a difference between "locally" flat and overall
As for the frequency range, it's DC to 50MHz. I already have parts to
do this, the Hall sensor is a thin film somehow bonded to ferrite
As for the accuracy I need, I was surprised to see the existing parts
were actually pretty sloppy. One of the pieces actually rocked back
and forth (barely so, but still perceptible) on my HD platter.
I didn't even need my micrometer to measure it either. One end of the
thing is 1 mil lower than the other, over a total of 176 mils.
So if I manually lap on a granite slab with a 3M lapping film, well,
how do I insure the work piece is not going to "rock" back and forth
as I move it?
A LONG time ago, I assembled FC fiber optic terminations. Once the
epoxy set, you put the FC connector in a steel puck and just rubbed
the FC/puck combo over a lapping film.
I would need suck a puck that fits my parts.
Is there a name for such a thing? The bottom of the puck was very
Probably close enough on the scale of a few inches.
Several different definitions.
Then you might find actual noise problems showing up if you get things
Might talk to either a rock and gem shop, or a jeweler.
You've tapped as much as I can help. Sorry. I'd try the parts raw
David A. Smith
Dear brian whatcott:
Truer words were never spoken. It is really common to establish air
gaps in transformer cores, for specific functions. He'd be better off
finding out if "lapping" were necessary first...
David A. Smith
I've put down the espressos and started to relax a bit.
I went to a kitchen supply store. No granite, but I bought a marble,
or something claiming to be marble, cheese cutting block. It's large
enough, and at any rate it was only 7$.
It certainly seems flat enough, I placed two of them shiny face
together and got that fun "vacuum cement" effect or whatever. There
was an airtight seal between the two.
I already have 600 grit sandpaper from my model rocket days.
We'll see as I go along what happens...