Phil wrote

...toroids which *must* be quite labour intensive

Why?

** More steps are involved in winding a toroidal - plus their manufacture
uses a special "shuttle" winding machine that can do only one tranny at a
time.


That doesn't have much bearing on how labour-intensive they are. You could say
much the same about many products made entirely by automated machinery involving
no hand work.

There is an anomoly in the common perception of China, incidentally. On the one
hand, it is said that they depend on cheap labour, and on the other that they
are likely to baulk at the prospect of making toroids because they are too
difficult. However, obviously if those difficulties can be overcome by intensive
labour, then one might expect the Chinese to favour toroids.

Another common assumption, and one that Patrick has made several times, is that
winding a toroid requires a shuttle. Not true...fortunately, because then the
machine really would be complicated.

The hard parts about making a toroid are clamping the workpiece, and traversing
the core with the bobbin. The machinery is more complex and expensive, and both
the machinery and the process are less versatile. Hence automation can only be
justified by large production runs of the same transformer.

Custom-wound toroids don't seem to be commonly offered. If the only problem was
the need for intensive labour, then they would be the perfect candidate for
boutique production. Actually they are just hard to make, no matter how you make
them.

R-cores have so many practical advantages it is a surprise how few you see
being used.

Yes, and come to think of it, why haven't they *always* been used? What are the
problems? They seem to be common when cast or pressed cores are used, but
winding strip into anything other than a toroid is fundamentally problematic.
How are the strips kept squashed together in the straight runs, and how does the
core keep its shape during and after the winding of the strip? Presumably it
must be annealed after winding and clamping, or bonded somehow. There is also
the need for precision-cutting of strip to a shape peculiar to each core size,
without leaving a burr on the edge. I wonder if that is done before or after the
insulating coating? That's quite a lot of tricky processing dedicated to each
core size.


Maybe that is about to change.

My recently acquired ( Asian made) CRO has one for example.

http://www.filespoint.com/point/2689...00578.JPG.html


Is that a strip-wound core?

cheers, Ian