[Halld-cal] 1st Article Update

[George Lolos]

As this week is coming to a close and the tenure of the student crew  
that worked on the construction of the 1st Article is also coming to  
an end, a brief update is in order.

As of today, 81 layers of lead and fibers have been built,  
corresponding to approximately 83 mm of matrix height.  Next week, the  
new crew of Co-op students will start so things will slow down a bit  
as they learn the techniques.

We have not seen any "serious" problems.   There's a slight (~1 mm)  
variation in height at different spots along the matrix and almost all  
of it comes from the first few layers, when the technique was still  
not learned.   We performed several diagnostic actions to determine  
its causes but nothing conclusive yet.  The fact that this variance  
remains constant and does not increase with built is a good omen.   
Maybe a fiber jumped its groove early on.  Once we machine the module  
and we can inspect the two end faces we can tell better.   In any  
case, we're within tolerances but we aim for perfection....

One thing that we have decided is that all Al base plates for the  
construction will be machined flat on the inner surface to assure an  
excellent base for the matrix and a reliable base for matrix height  
measurements.   Several other small improvements have been identified  
for the second press frame and they will be incorporated in the  
present one as well, where feasible.

So far, so good....

George