[Halld-tracking-hw] Carbn Fiber Parts
Curtis A. Meyer
cmeyer at ernest.phys.cmu.edu
Fri Jul 16 17:03:07 EDT 2010
I believe that 2:30 would work for us - curtis
On 7/16/10 4:56 PM, Tim Whitlatch wrote:
> Hello All,
>
> Now that we have got all the issues out, I propose we have a video
> conference Monday 2pm to discuss our next moves. Does that work for
> all interested parties?
> Enjoy the weekend!
> Thanks,
>
> Tim
>
> Curtis A. Meyer wrote:
>> Hi Everyone -
>>
>> yes, we are all planning to measure the position of the crimp pin
>> after stringing to get
>> the best possible accuracy. I am not contesting that. However, making
>> sure that that things
>> are as close as possible to where they should be should be our
>> starting point.
>>
>> When we were setting all the specifications on the parts and
>> hole, CMU wanted things
>> at the 1/2 mil level, but we had to back off due to cost. That said,
>> we had somewhat
>> reasonable expectation that we would fall somewhere near the middle
>> of the specs
>> with a distribution (like the Al parts) versus what we have with the
>> Carbon fiber where
>> we have parts just out side the specifications on the low side.
>>
>> When I take a donut and a feedthru, put them through the endplate
>> and feel the substantial
>> wiggle that is present. I a concerned to the point where I loose
>> sleep (seriously) over the
>> thought of continuing with these parts.
>>
>> As per the gas tightness, I believe that our small number of
>> controlled tests on a bench
>> appear to have sealed the donut to the feedthrough, but looking into
>> the straw at the glue
>> joint, there is some glue oozed into the straw. This is indicative of
>> what we saw when
>> we had gas leaks. We can also glue the feedthru to the endplate
>> sample, it is difficult to
>> check gas tightness, but we can look. However, even with that done, I
>> am worried about
>> guaranteeing all the seals holding in production.
>>
>> Our procedure, while controlled very well with the pneumatic
>> gluing and the entry and
>> exhaust ports is very good, but if we have wiggle in the parts during
>> installation, we have
>> trouble controlling things and I am very concerned about developing
>> gas leaks during the
>> experiment. I am not willing to say that we can do it with what we have.
>>
>> Tim's comment on the straws fitting is a good one. I also
>> recalled a tighter spacing
>> than the 9mil he recalls. That makes this much less of a problem.
>>
>> Curtis
>> On 7/16/10 2:49 PM, Tim Whitlatch wrote:
>>> Hi All,
>>>
>>> I will state what appears to be the 4 concerns and address each in
>>> order and offer a solution.
>>>
>>> 1) Uncertainty in the Position of wire.
>>>
>>> If all allowable tolerances are added up including the location of
>>> end plate holes, the uncertainty of wire position can be as much as
>>> .002+.002+.0025+.001+.003+.0025 = .013 inches.The uncertainty in the
>>> stereo wire positions can be as much as .014 inches. This includes
>>> all maximum clearance between mating parts and end plate hole locations
>>>
>>> *Possible solution*: As discussed last summer, the plan is to use
>>> either photogrammetry or a portable coordinate measurement machine
>>> to determine the as built locations of each crimp pin. This can
>>> probably get us to within knowing the actual location within
>>> about.003 inches.
>>>
>>> 2) Concern with gas seepage at joints.
>>>
>>> >From the average numbers supplied by CMU this morning;
>>> Clearance Fit between donut and straw is within .0027 with pin gage
>>> in place inches (.0032 without)* (drawings allow .004 inches)
>>> Clearance Fit between donut and feedthru is .0028 inches (drawings
>>> allow .004)
>>> Clearance Fit between feedthru and endplate is .0026 inches
>>> (drawings allow .0025)
>>>
>>> *Looks like the donut gets squeezed by .5 mil without pin gage while
>>> measuring
>>>
>>> >From above we note that the actual clearances are equal (within
>>> .0001 inches) or less than what was allowed by the drawings.
>>>
>>> *Possible solution:* It is important that we test the components in
>>> hand using the practice carbon end plate supplied by Meyer tool.
>>> Glue and leak check. This will tell us whether we have a problem or not.
>>>
>>> 3) Concern that the last straw will not be able to be installed due
>>> to lack of space.
>>>
>>> If allowable tolerances are added up for possible straw tube
>>> location discrepancies, we get .002+.002+.0025 = .0065 inches. For
>>> stereo holes this goes up to .0075. The minimum nominal clearance
>>> between any 2 straws is .009 inches (assuming maximum possible straw
>>> tube OD of .622 inches). Therefore, this has already been taken into
>>> consideration and does not pose a problem.
>>>
>>> *Possible Solution: *The last 3 straws in any row can be fit checked
>>> prior to gluing them in order to avoid any remote possibility that
>>> the last does not fit.
>>>
>>> 4) Crimp pin fit too tight
>>>
>>> *Solution:* Have vendor correct this.
>>>
>>> Cheers,
>>>
>>> Tim
>>>
>>> Curtis A. Meyer wrote:
>>>> Hi Beni
>>>>
>>>> run-out refers to the build up off all the errors as the parts are
>>>> put together.
>>>> Since they are all in the same direction, we get a build up rather than
>>>> a randomization.
>>>> I am not referring to glue seeping out, that does not happen. I'll try
>>>> to restat what we
>>>> feel the critical issue for us are that concern us a great deal with the
>>>> parts as they stand.
>>>>
>>>> The wire position relative to the endplate is indeed controlled by three
>>>> fits:
>>>>
>>>> 1) Feedthru into the endplate that we know is a sloppy fit right
>>>> now. It was comfortable
>>>> with these parts back in May, but they were shrunk by about 1.5
>>>> mils.
>>>> 2) The pin-holder into the feed-thru which is probably ok, although
>>>> is ok because
>>>> the two ridges on the side make it snug.
>>>> 3) The pin into the pin holder, which currently does not fit, so
>>>> this has to be changed.
>>>>
>>>> We think that this leads to 3-5 mil (75 to 125 micron) uncertainty
>>>> in the position.
>>>>
>>>> The second issue we are concerned about is the gas seal at the
>>>> downstream endplate.
>>>> This is where gas is fed into the straws, and if it simply leaks into
>>>> the large volume around
>>>> the straws here, we will not be able to guarantee what the gas is in the
>>>> straws themselves.
>>>> We know from our pretty serious looks at this with our prototypes that
>>>> the fit of the donut
>>>> into the straw and the feedthru into the donut are the major problem
>>>> areas and we had to
>>>> have things better than what we have with the current parts. Thus my
>>>> suggestion for the
>>>> 1 to 1.5 mil change in size. We also have a potential leak point where
>>>> the feed through
>>>> goes through the endplate. This is a loose fit now. This gluing is done
>>>> by "slathering" glue
>>>> on the feedthru, pushing it through the endplate into the donut,
>>>> cleaning up the glue around the
>>>> base at the endplate, then injecting glue into the port into the
>>>> feedthru-donut seal. Thus, I am
>>>> concerned about the seal from the endplate into the gas volume around
>>>> the straws as well.
>>>>
>>>> Finally, the layers with close pack are reasonably tight with the
>>>> straw positions. We left
>>>> about 5 mil between straws. Where this hits us is when we go around a
>>>> layer and then try
>>>> to fit the "last straw" in. If things have slid due to all the run-outs
>>>> plus the errors in the hole
>>>> positions themselves, then it may be impossible to load the last straw
>>>> in some layers without
>>>> damaging the chamber. I am not certain what our strategy to deal with
>>>> this would be other than
>>>> to plug the holes, don't insert the straw, and try to use the close-pack
>>>> layers to make the straw-to-straw
>>>> glue joints.
>>>>
>>>> We have been talking about alot since Tuesday and our conclusion
>>>> here is that we feel with these
>>>> three factors the risk is bigger than we are willing to accept.
>>>>
>>>> Curtis
>>>>
>>>> Hi Curtis,
>>>> I am a little confused here. What do you mean by run-out? Is this the
>>>> glue that
>>>> potentially can seep out? I also do not see where this 5 mil number for
>>>> the wire
>>>> location is coming from. I am totally confused. First you glue the donut
>>>> into the
>>>> straw and let it cure. So having the donuts undersized by 0.6mil in
>>>> diamter will lead
>>>> to a variation of not more that 0.3 mil in the location of the center
>>>> of the donut
>>>> that defines the location of the wire at this point. Then you put the
>>>> straw into the
>>>> frame and glue the feed through into it. At this point an 0.3mil toot
>>>> small feedthru
>>>> will cause a shift of 0.15mil in the central positon which defines the
>>>> wire location.
>>>> So now I am at max about 0.45 mil off center for the wire location or
>>>> the crimp
>>>> pin holder if you wish. I do not see how you could get to 5 mil.
>>>> Secondly this run-out if I understand correctly that this is glue
>>>> seeping out somewhere.
>>>> To try to mitigate such a problem by tighter tolerances is the wrong
>>>> approach. If this
>>>> is really a problem then the viscosity of the glue has to be changed. In
>>>> addition you do
>>>> not glue in only one straw at a time but many. One question here: When
>>>> you glue in
>>>> the straws into the frame is the frame vertically or horizontally. If it
>>>> is vertically this
>>>> isue of seeping glue to neighbouring straws is very unlikely. If
>>>> horizontally then start
>>>> from the bottom and work up on both sides of the ring then any seeping
>>>> will flow down
>>>> and only affect already installed straws.
>>>> Before doing any more modification I highly recommend to do some test
>>>> glueing with
>>>> straws and the carbon fire spare plate you used to test the reaming. If
>>>> all fits why try
>>>> to improve on something that works. We should try to optimize also on
>>>> the cost/benefit
>>>> ratio.
>>>>
>>>> cheers,
>>>> Beni
>>>>
>>>>
>>>>
>>
>>
>> --
>> 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/
>>
>>
--
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/
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