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nuckolls.bob(at)aeroelect
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 Posted: Fri Oct 28, 2011 8:39 am Post subject: microphone and headset jack insulating washers |
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At 10:48 AM 10/28/2011, you wrote:
| Quote: |
I just drilled a 3/8" hole for my headset jack in my aluminum panel
of my aluminum airframe. The threaded barrel fits through just fine.
I then grabbed the pair of insulating washers I'd gotten from B and
C. The shoulder washer has an ID of ~3/8", so it slips over the jack
just fine. Then I realized that to insulate the jack from the
airframe, the hole looks like it needs to be 1/2" for the shoulder
part of the washer to fit through the hole.
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Yep . . . that's how they work.
| Quote: | I thought I'd read that only a 3/8" hole is required. But if that's
the case, there's no room for a washer and the outside of the jack
would touch the metal, grounding it to the airframe.
I also read that some folks have not bothered with isolating washers
and there hasn't been any problems with ground loops.
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Your choice. The risks are low but not zero. Good
craftsmanship calls for the washers but tens of
thousands of Cessnas were built with the jacks
grounded to the airframe. Of course, nobody has
documented how many of those airplanes suffered
some form of ground loop noise that was either
inaudible over cabin noise or simply accepted
by the owner operator as "the way things are".
You can leave them off and conduct your own
experiment.
| Quote: | So if I'm going to use the insulating washers I'll have to see if
I've now got enough room for 1/2" holes and drill to that size.
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Are your clearances that tight? The O.D. on the
washers is something like 3/4". If you can use
the washers without trimming their edges for
clearance, then you probably have edge margins
for a 1/2" hole . . .
Bob . . .
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messydeer
Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA
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