On Fri, 04 Feb 2011 13:44:05 -0800, Winston
wrote:

wrote:

(...)

If you're building from scatch there is no point in usiing
silicon steel laminations. These are only needed to reduce eddy
current loss when using AC excitation.

With pure DC or rectified AC exicitation this is unnecessary -
solid soft iron or mild steel is just as good.

I was thinking in terms of relative permeability.
Steel at ca. 100 isn't quite as nice as silicon steel
at ca. 4000.

http://en.wikipedia.org/wiki/Magnetic_permeability#Values_for_some_common_mater ials


The simplest arrangement is to mill a long slot all the way along
one side of a rectangular bar of mild steel to leave an long U
section.

It can be excited by a single winding round the bottom of the U
or, slightly more efficiently (shorter mean turn length) by a
pair of windings - one on each vertical limb.

I like the double sets of pole pieces as shown in the Magnabend ad.
Lots of flux near the 'bending point' is good. Two concentrations
of flux tends to resist part yaw, too.


--Winston


The permeability figures quoted in your reference are for
quenched 0.9% carbon steel. This is not a mild steel but a high
carbon steel - file hard when quenched.

Mild steel is typically 0.1% carbon and magnetically pretty
similar to soft iron.

Jim