[Halld-tracking-hw] CDC Straw-tube size

[Curtis A. Meyer]

Hi Everyone -

   in the current design layout, we used a straw tube with the following 
Spec's:

   OD = 1.5875 cm                                   --> Outer Radius = 
0.79375 cm
   ID   = 1.5621 cm   -->  0.615 inches

   We then added 75 micron radial keep-out zone to yield an OR of 0.80125cm
or a keep-out diameter of 1.6025cm.  For exactly centered straws, this 
would
yield a spacing of just about 150 micron from wall-to-wall. (I say just 
about
because we really need to worry about small differences between 80-sided 
polygons
and circles).

   Finally, 150 microns corresponds to 5.9 mil.

   The end-plate specification on the true position of a hole is 5 mil. 
For people
like me, this means that the center can be anywhere in a 5 mil diameter hole
centered on the true position, or in the most extreme case, the straw 
could be
shifted by 2.5 mil (63.5 micron) in any direction.

   This is inside the 75 micron that we allowed in the design. The 
question comes
down to:

Do we want to add a bit more padding based on this specification? If so, 
by how much?
I could see adding another 25 micron of padding here, which would shrink 
the OD
by 50 microns.

   Cheers -- Curtis


-- 
Prof. Curtis A. Meyer		Department of Physics
Phone:	(412) 268-2745		Carnegie Mellon University
Fax:	(412) 681-0648		Pittsburgh PA 15213-3890 
cmeyer at ernest.phys.cmu.edu		http://www.curtismeyer.com/