wrote:
On Mon, 18 Apr 2011 06:28:24 -0700, Winston
wrote:

wrote:
On Sun, 17 Apr 2011 13:33:11 -0700, Winston
wrote:

Bob Engelhardt wrote:

The "Build Your Own Magnabend" section is available and it's very
interesting.

Alan reveals some very interesting stuff here that I suspected but
did not know for su

* The 'E' core is more efficient than the 'U' core.

* Clamping force for the 'E' core falls off significantly on the ends
because of the narrowed middle pole.

* Regular door hinges are a practical substitute for the complicated
biaxial set used on the commercial model.

Thanks again, Bob!

--Winston

Good stuff and very useful but I'm a bit worried by the simple
statement that the E core is more efficient.

A lot depends on both the assumptions made and the detail
design. The E core design may not necessarily the most efficient.
However the differences are not large enough to be important in
home brew projects.

Alan Unless you have very good milling facilities then I suggest
Alan that you go for a U-type magnet body. Although this design
Alan is not quite as efficient as an E-type body...

Given the inverse - cube character of magnetic attraction vs.
distance, it seems axiomatic that the two additional gaps
of the U core design should result in higher magnetic
reluctance than that of the E core, all else being equal.

Alan could be wrong on that point, I figured that he is in a
position to know, however....

--Winston

Just a few comments on magnetic attraction.

There is a comprehensive discussion in
http://en.wikipedia.org/wiki/Magnet

A brief summary may be useful.

I should have said "given the nonlinear relationship of
magnetic attraction vs. distance ...."
I see the situation more clearly now; thanks, Jim.

FWIW, I suspect that the flux density inside our solenoid
(cross-section radius *inside* the core) falls as the fourth
power of the distance from the windings, yes?

--Winston