[Halld-tracking-hw] Carbn Fiber Parts
Curtis A. Meyer
cmeyer at ernest.phys.cmu.edu
Mon Jul 19 07:59:56 EDT 2010
Hi Tim -
I believe that we should have the meeting at 2:30 -- curtis
On 7/19/10 7:49 AM, Tim Whitlatch wrote:
> Hi Curtis,
>
> We have a 3pm Hall D mtg. Would it be worth 1/2 hour anyway?
>
> Tim
>
> Curtis A. Meyer wrote:
>> 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/
>>
>>
--
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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