PSN-L Email List Message

Subject: RE: Tungsten Pins
From: "Gary Lindgren" gel@.................
Date: Mon, 23 Jun 2008 11:25:41 -0700


Meredith,

Refresh my memory of the '3 crossed rod pivot' concept, what does this look
like.

Gary 

 

 

 

 

From: psn-l-request@.............. [mailto:psn-l-request@............... On
Behalf Of meredith lamb
Sent: Friday, June 20, 2008 9:14 PM
To: psn-l@..............
Subject: Re: Tungsten Pins

 

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 

 












Meredith,

Refresh my memory of the ‘3 crossed rod = pivot’ concept, what does this look like.

Gary

 

 

 

 

From:= psn-l-request@.............. [mailto:psn-l-request@............... On = Behalf Of meredith lamb
Sent: Friday, June 20, 2008 9:14 PM
To: psn-l@..............
Subject: Re: Tungsten Pins

 

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.co= m/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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