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