CDC end-plate tolerances

[Beni Zihlmann <zihlmann@jlab.org>]

Hi Curtis,
I had another talk with Slava and Tim.
Slave implemented your numbers. He finds that for
layer 1 and 3 the gap between the straws in the layer is smaller than 
150 micro meters
also the gap between layer 1 and layer 2 straws and layer 3 and layer4 
straws in
the closed packed configuration are slightly smaller than 150micro meter.
the same is also true for layers 25 to 28.
other layers like 6/7, 18/19 and 22/23 the gap is just 150 microns plus 
some small value.
Slava makes the following point. This 150 micro meter accommodates the 
tolerance of
the outer diameter of  the straw. However, in addition to this we also 
have a tolerance of about 50 micro
meter from the machining of the end plate and then one could add another 
25 micro meter
assembling tolerance. so in total about 225 micro meter tolerance. This 
should be the nominal
gap between two straws in a layer and also between two layers at z=0.
Sorry this is my mistake I missed that point in the last meeting.
Slava can easily move the radius of the layers such that the 225 micro 
meter tolerance is
fulfilled everywhere and it still will fit into the CDC volume.
On the other hand there are some questions like what is the actual 
tolerance of the outer diameter
of the straws? is it 150 micro meter or is it maybe smaller or bigger?
One could even think of absorbing the machining and assembling 
tolerances into a 0.1mm smaller
outer diameter in the specifications of the straw going from 1.5875 cm 
to 1.5775 cm.
So we probably need to see what Tim will get from talking to potential 
manufacturers what
they can deliver. Maybe you can take some 20 tubes if you still have 
enough and measure the diameter
to get a feeling for what the tolerances might be. Also what is the 
tolerance on the bending?

cheers,
Beni

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Benedikt Zihlmann
TJNAF
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fax: 757 269 6331                zihlmann@jlab.org
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