There is so much wrong with Ian's post below that after considering it I'm not going
to even attempt to reply !

Cast and pressed cores my arse !

Graham


Ian Iveson wrote:

Graham wrote

They seem to be common when cast or pressed cores are used,

Eh ? Please give an example of a cast or pressed core !

Search for "amorphous core".

There are two ways of making amorphous cores. One is to cast a glassy strip and
wind it, and the other is to press a powder very hard. Generally it seems the
first is used for larger cores, presumably because of the problems of pressing
big things. I am assuming amorphous is a poor electrical conductor...?

As it happens, it looks like amorphous R-cores are most commonly made using cast
strip. I guess this is because the problems of winding small bobbins in-situ?

Searching under "amorphous core" or "r-core" gave very different results from
last time I tried. Seems like suddenly *everyone* has jumped on the bandwagon.

Anyway, pressed R-cores aren't as common as I thought, although pressed
amorphous toroids are. Cast amorphous strip-wound is increasingly common. I
would like to know how they clamp the straight sections to stop the laminations
springing out or buzzing.

The guys that make the cores and accesories have it sorted for sure. You need
to buy
a special winding machine too.

Of course, otherwise it would be labour-intensive. As it happens it is
complicated-and-expensive-machine-time-intensive. Quite possibly such machines
require more minding, I'll grant you that. I just wanted to dispel the notion
that they are all hand made, and that a shuttle is required. That would not be a
viable proposition.

The (relatively) simple method is to wind the wire on to a split bobbin in-situ
(as with an R-core), and then wind it off the bobbin onto the core. Clever eh?

As for the idea that R-cores are a recent "invention", I just don't see
it...pretty obvious idea don't you think? I assume that practical realisation
has been the sticking point. Perhaps the existing technology for strip-winding
toroidal cores could be adapted at relatively low cost.

cheers, Ian

Pooh Bear wrote

There is so much wrong with Ian's post below that after considering it I'm not
going
to even attempt to reply !

Cast and pressed cores my arse !

No, it's the previous post where I was a bit wrong, in that although some cores
use cast material, casting is not the process used to form the core. It is those
R-cores, cast and then wound, that I noticed have been commonly available for
some time. I have not been able to find any R-cores that are pressed, although
pressing is a common way of making other shapes of core.

Only small cores are pressed, such as for SMPS as far as I have been able to
discover, and I guess that R-cores are only feasible when they are relatively
large.

OTOH, I still have not determined how the legs of a strip-wound R-core are
clamped or bonded. Perhaps they have a pressed jacket? Then the final core
production
process would be pressing.

You may notice that I am asking questions, and you don't know the answers
any more than anyone else. That's OK, I don't expect you to know much about
production technology. It's just you might have saved me the effort if you
hadn't pretended you do. You may find some of your time better spent finding out
the truth and giving it some thought.

Just to recap, you said that production of toroidal transformers is labour
intensive and you wondered, given the advantages of R-cores, why they are not
more widely used. You suggested they are a recent invention.

In fact the production of toroidal transformers is no more labour intensive than
that of other kinds. Of course anything can be made in a more or less labour
intensive way. Take Patrick's EI transformers, for example, which are far more
labour intensive than the average toroid. Toroids actually favour machine
production, as Patrick testifies. They are especially hard to produce by hand.

R-core transformers have been fundamentally more difficult to produce. Whereas
you can muddle through with a toroid, the same can't be said of an R-core. The
core itself presents serious manufacturing problems, in contrast to a toroidal
core which is a doddle. It is not a matter of invention, the principle is
obvious. It is a matter of solving the difficulties of production.

Casting or pressing are processes which would normally be used to create such
shapes. Winding is pretty much the hardest way of making them. The only
fundamental reason they need to be wound if they are made of electrically
conducting material is to reduce eddy currents. It also happens that GOSS is
easier to make thin, and amorphous strip can *only* be made thin, so winding or
stacking makes use of convenient raw materials.

If you are not willing to learn, you may as well ignore my posts. If you can
contribute to my questions I would be grateful. Posturing will get you nowhere
in my estimation.

cheers, Ian



They seem to be common when cast or pressed cores are used,

Eh ? Please give an example of a cast or pressed core !

Search for "amorphous core".

There are two ways of making amorphous cores. One is to cast a glassy strip
and
wind it, and the other is to press a powder very hard. Generally it seems the
first is used for larger cores, presumably because of the problems of
pressing
big things. I am assuming amorphous is a poor electrical conductor...?

As it happens, it looks like amorphous R-cores are most commonly made using
cast
strip. I guess this is because the problems of winding small bobbins in-situ?

Searching under "amorphous core" or "r-core" gave very different results from
last time I tried. Seems like suddenly *everyone* has jumped on the
bandwagon.

Anyway, pressed R-cores aren't as common as I thought, although pressed
amorphous toroids are. Cast amorphous strip-wound is increasingly common. I
would like to know how they clamp the straight sections to stop the
laminations
springing out or buzzing.

The guys that make the cores and accesories have it sorted for sure. You
need
to buy
a special winding machine too.

Of course, otherwise it would be labour-intensive. As it happens it is
complicated-and-expensive-machine-time-intensive. Quite possibly such
machines
require more minding, I'll grant you that. I just wanted to dispel the notion
that they are all hand made, and that a shuttle is required. That would not
be a
viable proposition.

The (relatively) simple method is to wind the wire on to a split bobbin
in-situ
(as with an R-core), and then wind it off the bobbin onto the core. Clever
eh?

As for the idea that R-cores are a recent "invention", I just don't see
it...pretty obvious idea don't you think? I assume that practical realisation
has been the sticking point. Perhaps the existing technology for
strip-winding
toroidal cores could be adapted at relatively low cost.

cheers, Ian

Ian Iveson wrote:

Pooh Bear wrote

There is so much wrong with Ian's post below that after considering it I'm not
going
to even attempt to reply !

Cast and pressed cores my arse !

No, it's the previous post where I was a bit wrong, in that although some cores
use cast material, casting is not the process used to form the core. It is those
R-cores, cast and then wound, that I noticed have been commonly available for
some time. I have not been able to find any R-cores that are pressed, although
pressing is a common way of making other shapes of core.

Are you confusing pressing and stamping by any chance ? EI laminations are stamped
for sure.

As for casting, it plays no real roll in the production of GOSS. The material is
actually *rolled*. Sometimes called CRS ( cold rolled steel ).


Only small cores are pressed, such as for SMPS as far as I have been able to
discover,

Yes indeed. I don't know why you wanted to bring ferrites into this discussion. I
wasn't even sure if that was what you meant.


and I guess that R-cores are only feasible when they are relatively
large.

Really ? They start at about 15-20 VA.


OTOH, I still have not determined how the legs of a strip-wound R-core are
clamped or bonded. Perhaps they have a pressed jacket? Then the final core
production process would be pressing.

Uh ? The strip is wound and kept in shape by spot welding IIRC.


You may notice that I am asking questions, and you don't know the answers
any more than anyone else. That's OK, I don't expect you to know much about
production technology.

Eh ?

It's just you might have saved me the effort if you
hadn't pretended you do. You may find some of your time better spent finding out
the truth and giving it some thought.

I've used quite a few R-cores and I know plenty about their manufacture thanks.
Right down to internal safety margins and optimising winding area for lowest copper
losses.


Just to recap, you said that production of toroidal transformers is labour
intensive and you wondered, given the advantages of R-cores, why they are not
more widely used. You suggested they are a recent invention.

They are recent in relative terms.

In fact the production of toroidal transformers is no more labour intensive than
that of other kinds.

Utter nonsense.

Of course anything can be made in a more or less labour
intensive way. Take Patrick's EI transformers, for example, which are far more
labour intensive than the average toroid. Toroids actually favour machine
production, as Patrick testifies. They are especially hard to produce by hand.

R-core transformers have been fundamentally more difficult to produce.

Some aspects maybe.

Whereas
you can muddle through with a toroid, the same can't be said of an R-core. The
core itself presents serious manufacturing problems,

Transformer winders *buy* the cores ready made ! You *have* to use the dedicated
machiney - they realistically can't be hand wound.

in contrast to a toroidal
core which is a doddle. It is not a matter of invention, the principle is
obvious. It is a matter of solving the difficulties of production.

Casting or pressing are processes which would normally be used to create such
shapes.

What !!!!

Winding is pretty much the hardest way of making them. The only
fundamental reason they need to be wound if they are made of electrically
conducting material is to reduce eddy currents.

What steels used in cores have you come across that don't conduct ?

It also happens that GOSS is
easier to make thin, and amorphous strip can *only* be made thin, so winding or
stacking makes use of convenient raw materials.

That doesn't make any sense.

If you are not willing to learn, you may as well ignore my posts. If you can
contribute to my questions I would be grateful. Posturing will get you nowhere
in my estimation.

I'm certainly not going to learn anything about transformers from *you* nor do I
need to ! You have some very strange ideas.

Graham

"Pooh Bear"

Really ? They start at about 15-20 VA.

They are recent in relative terms.




** My old Brother dot matrix printer ( model 1102 ? ) used a 12 VA,
R-Core.

Bought it way back in 1983.

Seen several Asian hi-fi amps dating from the early 80s ( Luxman for one)
using 300 VA R-Cores made by Orion.



I'm certainly not going to learn anything about transformers from *you*
nor do I
need to ! You have some very strange ideas.



** Iveson is TROLLING ****WIT mental case.





........ Phil

Pooh Bear wrote

There is so much wrong with Ian's post below that after considering it I'm
not
going
to even attempt to reply !

Cast and pressed cores my arse !

No, it's the previous post where I was a bit wrong, in that although some
cores
use cast material, casting is not the process used to form the core. It is
those
R-cores, cast and then wound, that I noticed have been commonly available for
some time. I have not been able to find any R-cores that are pressed,
although
pressing is a common way of making other shapes of core.

Are you confusing pressing and stamping by any chance ? EI laminations are
stamped
for sure.

No I'm not. You are not very good at reading.

As for casting, it plays no real roll in the production of GOSS. The material
is
actually *rolled*. Sometimes called CRS ( cold rolled steel ).

Of course GOSS is not cast. If it is not cold-rolled or cold-drawn it is not
GOSS. Not *all* cold-rolled steel is GOSS, however, so CRS is not a sufficient
description. Neither is cold rolling the *only* method of making GOSS, although
it may be the only one used for GOSS transformer laminations.

Only small cores are pressed, such as for SMPS as far as I have been able to
discover,

Yes indeed. I don't know why you wanted to bring ferrites into this
discussion. I
wasn't even sure if that was what you meant.

Not a good enough excuse for saying they don't exist. I haven't mentioned
ferrites, either. You still haven't looked up amorphous, have you?

and I guess that R-cores are only feasible when they are relatively
large.

Really ? They start at about 15-20 VA.

Yes, really. Assuming you mean mains-frequency transformers, 15VA requires a
relatively large core compared to the pressed cores that I have found.

OTOH, I still have not determined how the legs of a strip-wound R-core are
clamped or bonded. Perhaps they have a pressed jacket? Then the final core
production process would be pressing.

Uh ? The strip is wound and kept in shape by spot welding IIRC.

Hmm, maybe. Welding is bad news for GOSS though, and for insulation, so if that
is the only way to do it, it detracts from the advantages. I wish I had enough
confidence in your knowledge and your discipline to believe you. Any references
to support your claim that spot welding is always used, and is sufficient
without any other form of bonding or clamping?

You may notice that I am asking questions, and you don't know the answers
any more than anyone else. That's OK, I don't expect you to know much about
production technology.

Eh ?

I said that's OK, I don't expect you to know much about production technology.

It's just you might have saved me the effort if you
hadn't pretended you do. You may find some of your time better spent finding
out
the truth and giving it some thought.

I've used quite a few R-cores and I know plenty about their manufacture
thanks.
Right down to internal safety margins and optimising winding area for lowest
copper
losses.

You don't need to know much about the production of an R-core to be able to do
those things, and I have little confidence in your estimation of what you can do
anyway. You often say you know things, but rarely say what you know, and when
you do it is often nonsense you read in a magazine, it seems to me.

Just to recap, you said that production of toroidal transformers is labour
intensive and you wondered, given the advantages of R-cores, why they are not
more widely used. You suggested they are a recent invention.

They are recent in relative terms.

They may be recent, we don't disagree there. They are not a recent invention,
however.

In fact the production of toroidal transformers is no more labour intensive
than
that of other kinds.

Utter nonsense.

It is utter nonsense to suggest that the production of one commodity requires
more labour than another, in general. Labour intensiveness depends on the
technology applied, not on the commodity. It is also nonsense to say that some
products can be made many at a time, and others only one at a time, for the same
reason. You are obviously not a production engineer, and you have no experience
or knowledge of production control or management.

Of course anything can be made in a more or less labour
intensive way. Take Patrick's EI transformers, for example, which are far
more
labour intensive than the average toroid. Toroids actually favour machine
production, as Patrick testifies. They are especially hard to produce by
hand.

R-core transformers have been fundamentally more difficult to produce.

Some aspects maybe.

Of course. It only takes one aspect to be difficult to make the whole thing
difficult though, doesn't it? You are squirming.

Whereas
you can muddle through with a toroid, the same can't be said of an R-core.
The
core itself presents serious manufacturing problems,

Transformer winders *buy* the cores ready made ! You *have* to use the
dedicated
machiney - they realistically can't be hand wound.

A non-sequitur if ever there was one. It's you that said that toroids are labour
intensive. Cores don't grow on trees, they have to be made before they are
bought. We were talking about the production of transformers, not just the
windings. Of course R-cores are relatively easy to wind. I have suggested that
must be offset against the relative difficulty of making the cores.

Patrick realistically hand-winds. When it comes to labour-intensive methods, EI
is easiest. Given a long strip of GOSS and some wire, I am sure that Patrick
could make a good toroidal transformer entirely by hand. I bet he couldn't make
a decent R-core though.

in contrast to a toroidal
core which is a doddle. It is not a matter of invention, the principle is
obvious. It is a matter of solving the difficulties of production.

Casting or pressing are processes which would normally be used to create such
shapes.

What !!!!

Tell me which bit you don't understand, and I will consider explaining it to
you. "Such shapes" refers to the R-core shape, BTW, which is not clear the way
you have quoted me.

Winding is pretty much the hardest way of making them. The only
fundamental reason they need to be wound if they are made of electrically
conducting material is to reduce eddy currents.

What steels used in cores have you come across that don't conduct ?

None. Why do you ask? Steel is not the only material that can be used to make a
core. Also I don't actually know whether amorphous is a good conductor, which is
why I asked. Do you? If you happen to have an amorphous core lying around,
perhaps you could check.

It also happens that GOSS is
easier to make thin, and amorphous strip can *only* be made thin, so winding
or
stacking makes use of convenient raw materials.

That doesn't make any sense.

Which part don't you understand? I will consider helping you if I can.

If you are not willing to learn, you may as well ignore my posts. If you can
contribute to my questions I would be grateful. Posturing will get you
nowhere
in my estimation.

I'm certainly not going to learn anything about transformers from *you* nor do
I
need to ! You have some very strange ideas.

Many truths seem strange to you, I am sure. Your life could be wasted if you
consistently refuse to learn on the grounds that you think you already know.
That is an illusion born of ignorance. It may have been blissful for a while,
but you are gambling with life. You may actually *need* to know something
sometime.

cheers, Ian

BTW, R-core is claimed as a trade mark by

http://www.kitamura-kiden.co.jp/english/

who reckon they introduced it to the world in 1978.

Why do they say it is round when it isn't? Presumably they mean rounded. The
cross-section is a rounded diamond shape, by the looks.

It may follow that the exact method of manufacture is unpublished. They have
loads of patents, they say. Is there anywhere on the net I can get copies of
patents for free?

Perhaps you, or anyone, can take a look at the core in this pictu

http://www.icl.co.jp/audio/english/RX40.htm

and suggest exactly how it is made. My guess is that the final forming is done
with a press, and I still can't see how it holds its shape unless the strip is
bonded along its whole length.

cheers, Ian

Ian Iveson wrote:

BTW, R-core is claimed as a trade mark by

http://www.kitamura-kiden.co.jp/english/

who reckon they introduced it to the world in 1978.

Yes, I believe that is correct. R-cores are also made by other suppliers under
license.


Why do they say it is round when it isn't? Presumably they mean rounded. The
cross-section is a rounded diamond shape, by the looks.

The cross section of the core itself is indeed round.


It may follow that the exact method of manufacture is unpublished. They have
loads of patents, they say. Is there anywhere on the net I can get copies of
patents for free?

If it's a US patent they are certainly available for free. Just Google.


Perhaps you, or anyone, can take a look at the core in this pictu

http://www.icl.co.jp/audio/english/RX40.htm

and suggest exactly how it is made. My guess is that the final forming is done
with a press, and I still can't see how it holds its shape unless the strip is
bonded along its whole length.

It's probably formed by winding on a mandrel I reckon.

Graham

On Mon, 19 Jun 2006 23:33:58 +0100, Pooh Bear
wrote:

There is so much wrong with Ian's post below that after considering it I'm not going
to even attempt to reply !

Cast and pressed cores my arse !

Graham


Ian Iveson wrote:

Graham wrote

They seem to be common when cast or pressed cores are used,

Eh ? Please give an example of a cast or pressed core !

Search for "amorphous core".

There are two ways of making amorphous cores. One is to cast a glassy strip and
wind it, and the other is to press a powder very hard. Generally it seems the
first is used for larger cores, presumably because of the problems of pressing
big things. I am assuming amorphous is a poor electrical conductor...?

As it happens, it looks like amorphous R-cores are most commonly made using cast
strip. I guess this is because the problems of winding small bobbins in-situ?

Searching under "amorphous core" or "r-core" gave very different results from
last time I tried. Seems like suddenly *everyone* has jumped on the bandwagon.

Anyway, pressed R-cores aren't as common as I thought, although pressed
amorphous toroids are. Cast amorphous strip-wound is increasingly common. I
would like to know how they clamp the straight sections to stop the laminations
springing out or buzzing.

The guys that make the cores and accesories have it sorted for sure. You need
to buy
a special winding machine too.

Of course, otherwise it would be labour-intensive. As it happens it is
complicated-and-expensive-machine-time-intensive. Quite possibly such machines
require more minding, I'll grant you that. I just wanted to dispel the notion
that they are all hand made, and that a shuttle is required. That would not be a
viable proposition.

The (relatively) simple method is to wind the wire on to a split bobbin in-situ
(as with an R-core), and then wind it off the bobbin onto the core. Clever eh?

As for the idea that R-cores are a recent "invention", I just don't see
it...pretty obvious idea don't you think? I assume that practical realisation
has been the sticking point. Perhaps the existing technology for strip-winding
toroidal cores could be adapted at relatively low cost.

cheers, Ian
I have a R-40 core and bobbin on my desk. The core was wound on a
rectangular mandrel. The first and last layers have been spot welded.

The core has been vacuum impregnated with a thin epoxy. It is very
well done. The core is rock solid.

The lamination strip width on the first and last turn is .195" in
width. The width of the center turn is .812".

The available winding area for one bobbin is only 1.542" x .125" which
isn't much concidering the size of the core.

This lamination is very similar in size to UI75 lamination as shown in
Tempel Steel Corp. book. www.Tempel.com

Economics dictated that we utilize the UI lamination design because
of the difference in the core cost and overall labor cost. We utilized
high speed bobbin winders and automated lamination stackers. The
stray flux emanation was lower in the R-Core but the UI was
acceptable.

I think that I made this comparison in the very late 1970s for a
medical instrument.

Jerry

Jerry said

I have a R-40 core and bobbin on my desk. The core was wound on a
rectangular mandrel. The first and last layers have been spot welded.

The core has been vacuum impregnated with a thin epoxy. It is very
well done. The core is rock solid.

The lamination strip width on the first and last turn is .195" in
width. The width of the center turn is .812".

The available winding area for one bobbin is only 1.542" x .125" which
isn't much concidering the size of the core.

This lamination is very similar in size to UI75 lamination as shown in
Tempel Steel Corp. book. www.Tempel.com

Economics dictated that we utilize the UI lamination design because
of the difference in the core cost and overall labor cost.

...We utilized
high speed bobbin winders and automated lamination stackers.

The
stray flux emanation was lower in the R-Core but the UI was
acceptable.

I think that I made this comparison in the very late 1970s for a
medical instrument.


Much thanks, Jerry.

Yes it is wrapped round a mandrel...that's the only way to use a single
continuous strip as far as I can see.

The key for me in your description is what I couldn't see from the pictures: the
adhesive filler.

If you wind strip round a mandrel, then no matter what the shape of the mandrel,
the winding will eventually end up round. I dimly remember there is even a law
devoted to this phenomenon. The less plastic the strip, the harder it is to
maintain the shape of the mandrel. GOSS is hard and elastic, hardly plastic at
all, and winding a shape with straight sides is impossible even for a few turns.

Even if you clamped the core and tack welded the ends of the strip, then when
you took it off the mandrel it would spring into an oval shape, with some
awkward wriggling round the welds.

That's why I suggested that the final process must be clamping, and bonding the
strip along its whole length. This could be done either by impregnation, or by
using coated strip, with the former being much easier if the results are good
enough.

I wonder if a notched mandrel is used? Otherwise it must be difficult to get
successive layers of wider strip to sit true on thinner ones. If so, then two
half-mandrels are required (or possibly four quarters), perhaps held apart so
that the straight sections of core are left free for the tack welding. Once
wound, the mandrels could be moved together to free the core, which would spring
into whatever shape it fancies.

Finally, I suggest, it is impregnated and then pressed to hold it in shape until
the adhesive filler goes off.

Is the cross-section round, BTW? It doesn't look round in the pictures.

cheers, Ian

On Sat, 24 Jun 2006 02:49:17 GMT, "Ian Iveson"
wrote:

Jerry said

I have a R-40 core and bobbin on my desk. The core was wound on a
rectangular mandrel. The first and last layers have been spot welded.

The core has been vacuum impregnated with a thin epoxy. It is very
well done. The core is rock solid.

The lamination strip width on the first and last turn is .195" in
width. The width of the center turn is .812".

The available winding area for one bobbin is only 1.542" x .125" which
isn't much concidering the size of the core.

This lamination is very similar in size to UI75 lamination as shown in
Tempel Steel Corp. book. www.Tempel.com

Economics dictated that we utilize the UI lamination design because
of the difference in the core cost and overall labor cost.

...We utilized
high speed bobbin winders and automated lamination stackers.

The
stray flux emanation was lower in the R-Core but the UI was
acceptable.

I think that I made this comparison in the very late 1970s for a
medical instrument.


Much thanks, Jerry.

Yes it is wrapped round a mandrel...that's the only way to use a single
continuous strip as far as I can see.

The key for me in your description is what I couldn't see from the pictures: the
adhesive filler.

If you wind strip round a mandrel, then no matter what the shape of the mandrel,
the winding will eventually end up round. I dimly remember there is even a law
devoted to this phenomenon. The less plastic the strip, the harder it is to
maintain the shape of the mandrel. GOSS is hard and elastic, hardly plastic at
all, and winding a shape with straight sides is impossible even for a few turns.

Even if you clamped the core and tack welded the ends of the strip, then when
you took it off the mandrel it would spring into an oval shape, with some
awkward wriggling round the welds.

That's why I suggested that the final process must be clamping, and bonding the
strip along its whole length. This could be done either by impregnation, or by
using coated strip, with the former being much easier if the results are good
enough.

I wonder if a notched mandrel is used? Otherwise it must be difficult to get
successive layers of wider strip to sit true on thinner ones. If so, then two
half-mandrels are required (or possibly four quarters), perhaps held apart so
that the straight sections of core are left free for the tack welding. Once
wound, the mandrels could be moved together to free the core, which would spring
into whatever shape it fancies.

Finally, I suggest, it is impregnated and then pressed to hold it in shape until
the adhesive filler goes off.

Is the cross-section round, BTW? It doesn't look round in the pictures.

cheers, Ian


Well Ian, I measured the R40 core and found that the diameter of the
core is 2.75". The dimensions are .873" x .830" and give me an area
value of 94.8% of that of a perfect circle, so I would say that you
could consider it to be circular in nature.

Consider that the very long strip of core material has to have a width
of .195" which progresses to .812" when at half length then the with
progressively narrows back to .195" on the last layer. That is some
piece of computer operated equipment that does that. I would like
to see their equipment.

If we assume the thickness of the material to be .006" GOSS, there
would be about 138 layer. The strip of steel would be 1013" long.

For those who might fight with my lack of exact math, It is hard
to get precise dimensions because of the bobin wound coil.

Jerry

Jerry wrote

Well Ian, I measured the R40 core and found that the diameter of the
core is 2.75". The dimensions are .873" x .830" and give me an area
value of 94.8% of that of a perfect circle, so I would say that you
could consider it to be circular in nature.

Consider that the very long strip of core material has to have a width
of .195" which progresses to .812" when at half length then the with
progressively narrows back to .195" on the last layer. That is some
piece of computer operated equipment that does that. I would like
to see their equipment.

If we assume the thickness of the material to be .006" GOSS, there
would be about 138 layer. The strip of steel would be 1013" long.

For those who might fight with my lack of exact math, It is hard
to get precise dimensions because of the bobin wound coil.

Thanks.

I tried to find their US patents, unsuccessfully as far as the
winding-round-a-rectangular-mandrel is concerned.

I did find two patents for how to wind the copper onto a torroid that were
interesting, and confirm that the hard parts are clamping the workpiece and
traversing the core with the spool.

I also found several patents concerning the winding of GOSS strip into toroids
of circular cross-section. Mandrels with semi-circular trenches are proposed,
and winding and grinding (gulp!) the strip at the same time. IIRC the R-core
site says the strip is slit, not ground.

A rectangular mandrel would snatch and slop, so I guess that forces separation
of the processes of shaping the strip and winding it. OTOH, a round
cross-section toroid has only one of the advantages of an R-co the core can
completely fill the copper winding with no gaps. It's still hard to wind the
copper.

I also came across several schemes for winding the core around the copper coils.
Quite a feat.

cheers, Ian