[Halld-tracking-hw] Carbn Fiber Parts
Tim Whitlatch
whitey at jlab.org
Mon Jul 19 07:49:44 EDT 2010
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/
>
>
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