Re: CDC end-plate tolerances

[Beni Zihlmann <zihlmann@jlab.org>]

Hi Curtis,
I hope I explain this right:
Slava uses 1.6025 cm OD for a straw and puts them into the drawing. Then
the rings of layer 2 overlapp with layer 1 by 44 micro meters. This is also
true for neighboring straws in layer 1. This means that the actual gap 
between
IDEAL straws with OD 1.5875 would be 106 micro meter and not 150 micro meter
between straws in layer 1 and straws between layer 1 and 2.

cheers,
Beni



> Hi Beni -
>
>      the OD of the straw (due to manufacturing) cannot be off more than
> the thickness of the tape on the outside (double wrapped). The way the 
> tubes are made, if the ID is right, the OD has to also be right --  it is just
> given by the material. With the straws that we looked at (about 80), the
> IDs were all very good. The OD's that we measuered were all good to about
> 25 microns and usually better (not 150 microns as indicated below).
>
>      We (Gary and I) feel that the 150 micron number is a fairly conservative 
> choice. Thus if we are only slightly smaller than 150 microns, I would consider 
> that to be fine. If however, we are much smaller (what do you see in layer's
> 1 and 3?), then I would be concerned. (Gary actually felt that 100 would be
> ok, but I held it at 150).
>
>   -- Curtis
> On Tue March 3 2009, Beni Zihlmann wrote:
>   
>> 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
>>
>>     
>
>
>
>