wrote:
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 'C-E-C' core has another advantage over the 'U' core
aside from reduced reluctance.

http://www.magnabend.com/advantages.html

Notice how the 'C' core features provide clamping force in the
left and right extreme sides of the pole piece.
Those four corners would have much less clamping force in a 'U
core configuration.

--Winston