PSN-L Email List Message

Subject: Re: Tungsten Pins
From: "meredith lamb" paleoartifact@.........
Date: Fri, 20 Jun 2008 22:14:26 -0600


Hi Chris and all,

I think I can now mentally see the very likelyhood of increased friction
with two rods and a ball over that of the
true 3 crossed rods pivot.  Being as the ball is set tightly in a straight
linear "groove" (inbetween the two rods), and
the horizontal pendulum/boom/pivot ball swings in a slight up-down arc there
would logically be some ball
arching response rotational rubbing friction of the ball on the two
rods trying to accomodate this motion of the
boom/mass.

Of course; if there was a straight linear motion of the pivot/boom/mass in
strict alignment with the two rods
and the ball pivot, the ball would simply rotate in a happier more
frictionless harmony.

Judging from all this rotaton arching nature of the traditonal Lehman; I
think it would logically be much better to
switch too, or use, the 3 crossed rod pivot.  By itself the 3 crossed rod
pivot is indeed a excellent choice for
a pivot with its ultra-low frictional loss.  This is only my choice; but
I've not tried them all.

Of course there is other pivots used in a Lehman which the builder has a
choice of using.  Conjecture on the
"best" of these will likely go on a long time.  Perhaps to ease this gap; it
could be possible to have the PSN
members simply do a undampened time duration of their announced variety of
seismometer pivot, by say a set amount
of offset (~ like 1/16" one side of the mass), and simply denote the amount
of time till the oscillations obviously
disappear on the traces from the normal background noise...this is simply a
indication of friction in the pivot.  Over time,
the "best" pivot variety would likely become more obvious.

I've mentioned it before; but I'll mention it again...The Sprengnether
"offset wire" pivot they used back in the 1950's,
for their horizontal seismometers has been rather a "lost" use pivot.
It falls in the torsion aspect as the music wire
slightly bends with boom/mass rotation.  Theres NO rods, steel/carbide balls
or mirror surface etc., required.  Probably
the best visual basic understanding demonstration of it is in John Lahrs
website; specifically for the solid ring and
wire shown.  If build rigidly, they can literally last "forever".
Personally I've never seen one break.  The science of
these isn't set in stone; so individual experimentation comes into
play....which can be fun to do.

http://www.jclahr.com/science/psn/gate.html
http://www.jclahr.com/science/psn/cor_psn.html

Take care, Meredith Lamb


On Wed, Jun 18, 2008 at 6:39 PM,  wrote:

>        I would like to see a run down pendulum test on this to check it.



>        Regards,
>
>        Chris
Hi Chris and all,
 
I think I can now mentally see the very likelyhood of increased friction with two rods and a ball over that of the
true 3 crossed rods pivot.  Being as the ball is set tightly in a straight linear "groove" (inbetween the two rods), and
the horizontal pendulum/boom/pivot ball swings in a slight up-down arc there would logically be some ball
arching response rotational rubbing friction of the ball on the two rods trying to accomodate this motion of the
boom/mass.
 
Of course; if there was a straight linear motion of the pivot/boom/mass in strict alignment with the two rods
and the ball pivot, the ball would simply rotate in a happier more frictionless harmony.
 
Judging from all this rotaton arching nature of the traditonal Lehman; I think it would logically be much better to
switch too, or use, the 3 crossed rod pivot.  By itself the 3 crossed rod pivot is indeed a excellent choice for
a pivot with its ultra-low frictional loss.  This is only my choice; but I've not tried them all.
 
Of course there is other pivots used in a Lehman which the builder has a choice of using.  Conjecture on the
"best" of these will likely go on a long time.  Perhaps to ease this gap; it could be possible to have the PSN
members simply do a undampened time duration of their announced variety of seismometer pivot, by say a set amount
of offset (~ like 1/16" one side of the mass), and simply denote the amount of time till the oscillations obviously
disappear on the traces from the normal background noise...this is simply a indication of friction in the pivot.  Over time,
the "best" pivot variety would likely become more obvious.
 
I've mentioned it before; but I'll mention it again...The Sprengnether "offset wire" pivot they used back in the 1950's,
for their horizontal seismometers has been rather a "lost" use pivot.  It falls in the torsion aspect as the music wire
slightly bends with boom/mass rotation.  Theres NO rods, steel/carbide balls or mirror surface etc., required.  Probably
the best visual basic understanding demonstration of it is in John Lahrs website; specifically for the solid ring and
wire shown.  If build rigidly, they can literally last "forever".   Personally I've never seen one break.  The science of
these isn't set in stone; so individual experimentation comes into play....which can be fun to do.
 
http://www.jclahr.com/science/psn/gate.html
http://www.jclahr.com/science/psn/cor_psn.html 
 
Take care, Meredith Lamb

 
On Wed, Jun 18, 2008 at 6:39 PM, <ChrisAtUpw@.......> wrote:
       I would like to see a run down pendulum test on this to check it. 
 
       Regards,

       Chris


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