Jan and Ron,
I will not be at the meeting tomorrow but would like to mak this brief
report.
 
At wpmtg117, we discussed the possibility of increasing the endplate
thickness beyond 100mm. I have run the FEA for thicknesses
30,50,75,100,125,150 and 175. The short stoy is that there is little
advantage to increasing the thickness beyond 100mm.
 
In the range from 30 to 75mm thickness, the deflection varies closely to
a power (t**-1.5), slightly different from my expectation of (t**-2). At
100mm, the deflection already deviated from following the power; the
deflection at 100mm is more than expected from (t**-1.5). The
improvement from 125mm to 150mm is quite small.
 
The the root cause of the breakdown of the (t**-1.5) variation can be
seen in my presentation, wpmtg117, 20101111, page 4, bottom figure. The
elements of the back-plate do not remain straight in rows 1 and 8; they
are buckling between the spaceframe-separator-plates. This only get
worse at larger thickness. At 175mm thickness, although the FEA solution
looked to be following the trend, the FEA complained that the solution
might be garbage.
 
The increase in thickness comes with an increase in material because
the  spaceframe-separator-plates are getting longer. Alternatively, the
extra material can go into the back-plate. Increasing the backplate
thickness from 3mm to 4mm provides a decrease in deflection similar to
increasing the thickness to 150mm. This is preliminary and not optimized.
 
Dan