Hi Chris,    The sensor is coming along nicely. =20
Q.   The coil is done, is it a good idea to coat the coil with glue or =
something like that just to keep the wires from getting damaged, or is =
it best just to leave it?
Q.  As the wires leave the coil and travel down the shaft to the lower =
pivot, what is the best way to make the transition off the shaft to the =
base?  I have seen coiled wires to form a spring, to reduce drag on the =
movement of the shaft.  I have seen large loops and small coils.  I =
don't know if they should be hanging down or left and right.  You must =
have tried several different methods?

Thanks, Ted



----- Original Message -----=20
  From: ChrisAtUpw@..........
  To: psn-l@.................
  Sent: Thursday, October 05, 2006 8:59 PM
  Subject: Re: Building a lehman seismometer


  In a message dated 2006/10/05, tchannel@.............. writes:


       I am in the process of building a sensor bases on your prototype, =
and great drawings. I have most of the parts located, again with your =
help and others on the mailing list. I will send pictures as I go along, =
if you like, and if you tell me how to send them.


  Hi Ted,

         gif or jpg images would do fine to my EMail address.


    I regards to the angle between the bottom and top hinge, a fraction =
of a degree, how do you measure for that? Or do you adjust and measure =
the period, instead?


         I don't measure it, I calculate it. Then I make the structure =
so that there is a small amount of adjustment. The axis is defined by =
the centre of the ball and the edge of the top wire clamp. You vary the =
slope of the long horizontal baseplate to set the period accurately, =
using the end adjustment screw, but you keep the arm parallel to the =
baseplate.=20


    Chris, I see on your drawing you did not need to brace the vertical =
arm of your device. Looks very strong.  How did you attach that vertical =
to the cross member?


         In my case the bottom of the vertical was milled flat and then =
the centre sections were milled out ~15 thou so that there were four =
longitudinal narrow strips about 1/16" wide x 3/4" long at the corners. =
Then two bolts were put through the cross bar, the long base and =
threaded into the vertical at the front and back ends. If you don't mill =
out / file out the centre sections, the clamp force will be at the =
centre, not at the edges where you want it and it will rock just enough =
to give trouble. An alternative is to use a flat end and 3 or 4 shim =
strips.
         You can also make three point suspensions, or you can glue the =
vertical to the long base with two part modified acrylic glue. This is =
strong and tough, unlike epoxy which is brittle. However you have to be =
very quick as it has a gel time of about a couple of minutes in a warm =
room.=20
         An alternative construction might be to use a 3" dia tube for =
the vertical? This can be held on either with a central vertical =
threaded rod and a top plate, or by mounting a 3/4" circular rod =
horizontally through two holes in the vertical tube, drilling and =
tapping this and putting a vertical bolt up through the baseplate. You =
would make three contact strip suspension flats at 120 deg.
         You can use an SS ball on a carbide flat lower hinge or crossed =
cylinders. You can buy 1/8" solid tungsten carbide drills from =
www.Smallparts.com or www.Digikey.com and cut the shanks to length with =
a carbide disk. Glue one to the head of an SS bolt and the other to the =
end of the arm with two part modified acrylic glue. I usually file a =
shallow V first to locate the shank mechanically. Mount the vertical rod =
or the ball on vertical support and the horizontal rod or the flat on =
the arm, NOT the other way around! 8 thou Nickel plated piano wire is =
available for mandolin strings at a music shop. See www.daddario.com
      Another method of construction which you might wish to consider? =
In this I used Al alloy U channel, 3" wide x 1" high and three =
triangular 3/16" to 1/4" thick corner plates at the end T / L joint. The =
vertical is attached to the long horizontal base with two 5" corner =
plates and four SS bolts per plate. I use two plain SS washers and a =
spring washer per bolt to prevent it digging into the softer Al. The =
open U is on the inside of the 90 deg joint. The cross bar is attached =
to the outside of the vertical with four bolts and a 7" triangle. It =
seems to work OK and makes quite a neat job. I bought it cut / chopped =
to size, from a local metals supermarket. You maybe able to get 2" x 1" =
U channel from building supplies / DIY. I tend to make things more =
massive than absolutely necessary. The secret of the rigidity is mostly =
in the three large triangular joint plates.=20
      I tend to use 18" to 24" long tubular arms. 22" gives a 1.5 sec =
basic pendulum which you can extend by x20 to 30 sec. 3 ft is a bit =
bulky, but it gives maybe 40 sec or more? You can get compression =
fittings for most tube. I use 1/2" SS water pipe and brass water =
fittings, 15mm OD, but the tube may not be widely available? It is light =
but rigid and non magnetic. Hard drawn Cu or brass are alternatives. You =
can also buy general purpose brass compression 'engineering' fittings =
for a wide range of standard pipe sizes, but these may only be available =
through a few more specialist suppliers and they tend to be more =
expensive than water fittings. Check on the availabilty of thin wall =
welded SS water pipe?=20

      Regards,

      Chris Chapman   =20







Hi Chris,    The sensor =
is coming=20
along nicely.  
Q.   The coil is done, is it =
a good idea=20
to coat the coil with glue or something like that just to keep the wires =
from=20
getting damaged, or is it best just to leave it?
Q.  As the wires leave the coil =
and travel=20
down the shaft to the lower pivot, what is the best way to make the =
transition=20
off the shaft to the base?  I have seen coiled wires to form a =
spring, to=20
reduce drag on the movement of the shaft.  I have seen large loops =
and=20
small coils.  I don't know if they should be hanging down or left =
and=20
right.  You must have tried several different methods?
 
Thanks, Ted
 
 
 
----- Original Message ----- 

  From:=20
  ChrisAtUpw@....... 
  
To: psn-l@.............. 
  
Sent: Thursday, October 05, =
2006 8:59=20
  PM
  
Subject: Re: Building a lehman=20
  seismometer
  

In a=20
  message dated 2006/10/05, tchannel@..............=20
  writes:


     I am in the process of building a sensor =
bases on=20
    your prototype, and great drawings. I have most of the parts =
located, again=20
    with your help and others on the mailing list. I will send pictures =
as I go=20
    along, if you like, and if you tell me how to send them.

Hi=20
  Ted,

       gif or jpg images =
would do=20
  fine to my EMail address.


  I regards to the angle between the bottom and top hinge, =
a=20
    fraction of a degree, how do you measure for that? Or do you adjust =
and=20
    measure the period, instead?

       I don't=20
  measure it, I calculate it. Then I make the structure so that there is =
a small=20
  amount of adjustment. The axis is defined by the centre of the ball =
and the=20
  edge of the top wire clamp. You vary the slope of the long horizontal=20
  baseplate to set the period accurately, using the end adjustment =
screw, but=20
  you keep the arm parallel to the baseplate. 


  Chris, I see on your drawing you did not need to brace =
the=20
    vertical arm of your device. Looks very strong.  How did you =
attach=20
    that vertical to the cross member?

       In my=20
  case the bottom of the vertical was milled flat and then the centre =
sections=20
  were milled out ~15 thou so that there were four longitudinal narrow =
strips=20
  about 1/16" wide x 3/4" long at the corners. Then two bolts were put =
through=20
  the cross bar, the long base and threaded into the vertical at the =
front and=20
  back ends. If you don't mill out / file out the centre sections, the =
clamp=20
  force will be at the centre, not at the edges where you want it and it =
will=20
  rock just enough to give trouble. An alternative is to use a flat end =
and 3 or=20
  4 shim strips.
       You can also =
make three=20
  point suspensions, or you can glue the vertical to the long base with =
two part=20
  modified acrylic glue. This is strong and tough, unlike epoxy which is =

  brittle. However you have to be very quick as it has a gel time of =
about a=20
  couple of minutes in a warm room. =

       An=20
  alternative construction might be to use a 3" dia tube for the =
vertical? This=20
  can be held on either with a central vertical threaded rod and a top =
plate, or=20
  by mounting a 3/4" circular rod horizontally through two holes in the =
vertical=20
  tube, drilling and tapping this and putting a vertical bolt up through =
the=20
  baseplate. You would make three contact strip suspension flats at 120=20
  deg.
       You can use an SS ball on =
a=20
  carbide flat lower hinge or crossed cylinders. You can buy 1/8" solid =
tungsten=20
  carbide drills from www.Smallparts.com or www.Digikey.com and cut the =
shanks=20
  to length with a carbide disk. Glue one to the head of an SS bolt and =
the=20
  other to the end of the arm with two part modified acrylic glue. I =
usually=20
  file a shallow V first to locate the shank mechanically. Mount the =
vertical=20
  rod or the ball on vertical support and the horizontal rod or the flat =
on the=20
  arm, NOT the other way around! 8 thou Nickel plated piano wire is =
available=20
  for mandolin strings at a music shop. See =
www.daddario.com
    =
Another method of =
construction=20
  which you might wish to consider? In this I used Al alloy U channel, =
3" wide x=20
  1" high and three triangular 3/16" to 1/4" thick corner plates at the =
end T /=20
  L joint. The vertical is attached to the long horizontal base with two =
5"=20
  corner plates and four SS bolts per plate. I use two plain SS washers =
and a=20
  spring washer per bolt to prevent it digging into the softer Al. The =
open U is=20
  on the inside of the 90 deg joint. The cross bar is attached to the =
outside of=20
  the vertical with four bolts and a 7" triangle. It seems to work OK =
and makes=20
  quite a neat job. I bought it cut / chopped to size, from a local =
metals=20
  supermarket. You maybe able to get 2" x 1" U channel from building =
supplies /=20
  DIY. I tend to make things more massive than absolutely necessary. The =
secret=20
  of the rigidity is mostly in the three large triangular joint plates.=20
  
    I tend to use 18" to 24" long tubular arms. 22" =
gives a=20
  1.5 sec basic pendulum which you can extend by x20 to 30 sec. 3 ft is =
a bit=20
  bulky, but it gives maybe 40 sec or more? You can get compression =
fittings for=20
  most tube. I use 1/2" SS water pipe and brass water fittings, 15mm OD, =
but the=20
  tube may not be widely available? It is light but rigid and non =
magnetic. Hard=20
  drawn Cu or brass are alternatives. You can also buy general purpose =
brass=20
  compression 'engineering' fittings for a wide range of standard pipe =
sizes,=20
  but these may only be available through a few more specialist =
suppliers and=20
  they tend to be more expensive than water fittings. Check on the =
availabilty=20
  of thin wall welded SS water pipe? 

    =
Regards,

    Chris=20
  Chapman    =