PSN-L Email List Message

Subject: Re: Another horizontal boom/mast pivot to consider
From: "Frank Cooper" fxc@.......
Date: Fri, 22 Nov 2002 13:50:43 -0600


OK Cap as a member of the "these people" or the "they" ball bearing =
party, I'll bite,
I'll respond even though I think your purpose is to have a little fun =
and stir the pot a bit. Perhaps we take ourselves too seriously at times =
since "we" all enjoy and are all engaged in a very interesting HOBBY.  I =
have to differ with you on a couple of statements in your recent =
postings.  You say "John Lahr's completely frictionless Sprengnether =
type wire-under-tension pivot is much better than ball bearings and just =
as easy, if not easier to make, and it stays put rather than slithering =
around like ball bearings."

Have you ever used the ball bearing method?  I assume you must speak =
from long experience to back-up your slithering ball bearing =
pronouncement.  I have been using a ball bearing at the pivot point of =
my Lehman pendulum for years and it has not "slithered around" once.  =
But perhaps I should only "claim." Maybe you also have long experience =
in maintaining a 30 second period with a modified ball bearing Lehman.  =
However, that must not be the case since you say "I don't see how they =
could possibly get month's-long stability at 30-40 second periods as has =
been claimed in recent postings."  My only suggestion is to try it --- =
you might like it and become "one of these people."=20

And you say "My guess is what these people actually have are =
strong-motion detectors rather than the Lehmans they think they have."  =
You speak from the abyss --- you evidently do not check the posting of =
teleseismic events by "these people.". "They" speak louder than your =
words.  Perhaps even louder than "they think they have."

Regards to all and a Merry Christmas!

Frank Cooper, Friendswood, Texas, USA

Seismology web site at  http://pages.prodigy.net/fxc/







----- Original Message -----=20
  From: CapAAVSO@..........
  To: psn-l@.................
  Sent: Friday, November 22, 2002 10:34 AM
  Subject: Re: Another horizontal boom/mast pivot to consider


  In a message dated 11/21/02 8:01:16 AM GMT Standard Time, =
meredithlamb@............. writes:



    With all the discussion on a horizontal boom/mast pivot, it
    might be alot simpler to use/make another type mentioned in
    the past emails.  Its based on the Sprengnether horizontals
    general design and has been "revised" for use by John Lahr
    on his horizontal; but it essentially is the same type pivot.
    .............I think its one of the best pivot innovations I know =
of,
    and most ingenious of John to come up with the variation.
    Theres probably about zero long term problems with this
    conpared to other pivot designs.  Its frictionless as
    John describes in his text.


  Hi Meridith

  You don't have to be an engineer to realize friction in the lower =
pivot of a Lehman will decrease its sensitivity. Lehman I'm sure was =
aware of that but he was designing a simple instrument for amateurs that =
was good enough to get started. The point-in-a -dimple bottom pivot will =
always have some stick-slip friction which will interfere with its =
sensitivity to small earthquake movements. if you replace the point with =
a ball its rolling friction is less but nevertheless there will still be =
small residual stick-slip friction. John Lahr's completely frictionless =
Sprengnether type wire-under-tension pivot is much better than ball =
bearings and just as easy, if not easier to make, and it stays put =
rather than slithering around like ball bearings. I use John Lahr's =
system with 0.008" music wire, obtainable from any music store, and it =
shows the finest detail in the microseisms if I turn up the gain. =
However, and this is important, even with frictionless pivots my Lehman =
is unstable over time unless I set its period for about 10-15 seconds. I =
doubt anyone can do much better with ball bearing pivots unless they are =
on bed rock and even then I don't see how they could possibly get =
month's-long stability at 30-40 second periods as has been claimed in =
recent postings. My guess is what these people actually have are =
strong-motion detectors rather than the Lehmans they think they have.

  Best regards,
  Cap








OK Cap as a member of the "these people" or the = "they"=20 ball bearing party, I'll bite,
I'll respond even though I think your purpose = is to have=20 a little fun and stir the pot a bit. Perhaps we take ourselves too=20 seriously at times since "we" all enjoy and are all engaged in = a very interesting HOBBY.  I have to differ with you on a = couple of=20 statements in your recent postings.  You say "John Lahr's = completely=20 frictionless Sprengnether type wire-under-tension pivot is much better = than ball=20 bearings and just as easy, if not easier to make, and it stays put = rather than=20 slithering around like ball bearings."
 
Have you ever used the ball bearing method?  I = assume you=20 must speak from long experience to back-up your slithering ball = bearing=20 pronouncement.  I have been using a ball bearing at the pivot point = of my=20 Lehman pendulum for years and it has not "slithered around" = once.  But=20 perhaps I should only "claim." Maybe you also have long experience in=20 maintaining a 30 second period with a modified ball bearing = Lehman. =20 However, that must not be the case since you say "I don't see how they = could=20 possibly get month's-long stability at 30-40 second periods as has been = claimed=20 in recent postings."  My only suggestion is to try it --- you might = like it=20 and become "one of these people."
 
And you say "My guess is what these people actually = have are=20 strong-motion detectors rather than the Lehmans they think they = have."  You=20 speak from the abyss --- you evidently do not check the posting of = teleseismic=20 events by "these people.". "They" speak louder than your words.  = Perhaps=20 even louder than "they think they have."
 
Regards to all and a Merry Christmas!
 
Frank Cooper, Friendswood, Texas, USA
 
Seismology web site at  http://pages.prodigy.net/fxc/<= BR>
 
 
 
 
 
----- Original Message -----
From:=20 CapAAVSO@.......=20
To: psn-l@..............
Sent: Friday, November 22, 2002 = 10:34=20 AM
Subject: Re: Another horizontal = boom/mast=20 pivot to consider

In a message dated 11/21/02 8:01:16 AM GMT = Standard Time,=20 meredithlamb@.............= =20 writes:


With all the discussion on a horizontal boom/mast pivot, = it
might be alot simpler to use/make another type mentioned = in
the=20 past emails.  Its based on the Sprengnether = horizontals
general=20 design and has been "revised" for use by John Lahr
on his = horizontal; but=20 it essentially is the same type pivot.
.............I think its = one of=20 the best pivot innovations I know of,
and most ingenious of John = to come=20 up with the variation.
Theres probably about zero long term = problems with=20 this
conpared to other pivot designs.  Its frictionless = as
John=20 describes in his text.

Hi Meridith

You = don't have=20 to be an engineer to realize friction in the lower pivot of a Lehman = will=20 decrease its sensitivity. Lehman I'm sure was aware of that but he was = designing a simple instrument for amateurs that was good enough to get = started. The point-in-a -dimple bottom pivot will always have some = stick-slip=20 friction which will interfere with its sensitivity to small earthquake = movements. if you replace the point with a ball its rolling friction = is less=20 but nevertheless there will still be small residual stick-slip = friction. John=20 Lahr's completely frictionless Sprengnether type wire-under-tension = pivot is=20 much better than ball bearings and just as easy, if not easier to = make, and it=20 stays put rather than slithering around like ball bearings. I use John = Lahr's=20 system with 0.008" music wire, obtainable from any music store, and it = shows=20 the finest detail in the microseisms if I turn up the gain. However, = and this=20 is important, even with frictionless pivots my Lehman is unstable over = time=20 unless I set its period for about 10-15 seconds. I doubt anyone can do = much=20 better with ball bearing pivots unless they are on bed rock and even = then I=20 don't see how they could possibly get month's-long stability at 30-40 = second=20 periods as has been claimed in recent postings. My guess is what these = people=20 actually have are strong-motion detectors rather than the Lehmans they = think=20 they have.

Best=20 regards,
Cap

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