alternating magnetic polarities n s n s for simplicity of illustration as described in reference to fig1 the respective alternating magnetic polarities of the soft magnet blocks are the result of the alternating n s magnetic polarities through the thicknesses of the permanent magnet plates 28 when four soft magnet block chuck layers 40 42 are placed on top of each other such that overlying underlying soft magnet blocks are of opposite n s magnetic polarity as indicated in fig2 a the resulting magnetic flux lines are close circuited among the magnetically soft iron blocks so that the chuck as a whole layers 40 42 is completely balanced and neutralized magnetically the close circuited magnetic flux line pattern 44 is illustrated below chuck layers 40 42 as part of fig2 a in this orientation of chuck layers 40 42 the assembled chuck is now in the u201c magnetically inactive u201d state and it will not exert significant attractive force on an external ferromagnetic object however if top chuck layer 40 is rotated 90 u00b0 such that overlying underlying soft magnet blocks are of the same polarities n u2014 n and s u2014 s of the two layers are now aligned as illustrated in fig2 b the magnetic circuits of clutch layers 40 42 are incomplete and remain open the magnetic flux pattern 46 of the rotated chuck layer assembly is illustrated in fig2 b the magnetic chuck comprising chuck layers 40 42 is in the u201c magnetically active u201d state and will need to attach an external object to complete the flux loop because of the particular arrangement of the permanent magnet plates 28.