On Sun, 06 Feb 2011 15:55:54 -0500, Joseph Gwinn
wrote:

Snip
I would be tempted to fabricate the magnetic circuit components by
bolting together four pieces of 1018 steel rectangles: one wide 0.5"
thick piece to form the bottom, two 0.5" thick pieces to form the
outsides, and one 1.0" thick piece to form the center, roughly following
the outline shown in the MagnaBend literature.

This will be a considerable savings on steel material, and on machining
effort.

Bolting-together would be accomplished using hex socket flat head
machine screws through the bottom piece screwed into drilled and tapped
holes in the steel center and side pieces.


Joe Gwinn.


Your fabricated construction should be fine. Although there are
two additional residual air gaps in the magnetic circuit these
are hard bolted gaps dropping to zero near every bolt and would
not add significantly to the series of four main residual gaps
that occur between the pole pieces and the work piece.

A further simplification would be to revert to the U
configuration. but with a single coil on the lower bar of the U
(or on the U leg remote from the bend line). This is slighly less
efficient than a coil on each leg because of the longer mean
turn length but this is more than compensated for by the ability
to locate the full sized pole piece where it matters most -
close to the bend line.

The width of the U is an interesting free variable. It makes
little difference to the total reluctance but a longer lower bar
both increases the available winding area and exerts the bending
force at a longer lever arm. On this basis - the longer the
better. For this application a gap in the U about equal to the
limb width looks like a reasonable choice.

There is no special compensating advantage in a longer limb
length so these should only be long enough to give sufficient
winding area.For the above U size, limbs long enough to give an
approximately square winding area would be appropriate.


Jim