wrote:
On Thu, 03 Feb 2011 17:54:24 -0800, Winston
wrote:

(...)

I can envision both possibilities:
The attraction to the clamping bar would be improved
because the resulting field distortion would tend to
push the lines of flux outwards from each electromagnet.

The attraction to the clamping bar would be hindered
because of magnetic 'phase cancellation' between the
magnets.

I'm tending towards the latter opinion.


--Winston


Yes they would try to repel each other and this is desirable.

If the second south pole was not present, some of the available
flux would be radiated uselessly sideways. The presence of the
second south pole forces this flux back into the wanted
direction.

(...)

So, the first - prize answer doesn't involve MOTs.
(Unless one is building a *very* narrow bender, of course.)

*Ideally speaking* in terms of raw performance, one
would fabricate a stackup of silicon 'transformer iron'
laminations in the form of a single, very thick 'C-E-C' core,
then secure a single rectangular winding in the gap.

Look, for example at the magnetic pole pieces in the
Real Thing: http://www.magnabend.com/advantages.html

Then one would pot the windings and surface-grind the
face of this electromagnet to hinder swarf from
short-circuiting the magnetic path.

By Jove, I think I've got it!

--Winston -- Prolly less expensive to just buy one.