Hi all,

Yesterday, I tried the simplest hinge (the two outer rod support/contacts)
configuration
using the most commonly available material I could think of. Its simply
acouple of bolts
of a common 2.5" length, with 1/4" diameter, where only part of the length
(.750")
is threaded, and the rest of the length is of a round rod out to the hex
shaped bolt
head. The threaded end is inserted or screwed into a piece of square metal
rod.
This leaves the smooth round exposed rod and of course the bolt head
extended
outward with no bolt head support. I used a rusty rectangular block of stee=
l
that
already had two separated threaded holes, that matched the thread of the tw=
o
bolts
for this test. They were firmly screwed into the steel to where the thread
ends.
Another way of visualizing such, is to imagine a coat hangar on a wall with
its
base frame...but with only two extending rods/shafts thereon. The only bolt
surface
smoothing action I took was to mount the bolts in a drill press chuck, and
sand
the round bolt surfaces with a 400 grit strip of sandpaper for acouple
minutes each.

For this test, the two rod hinge is orientated so it was for a S-G; or a
hanging
pendulum. The actual crossed rod/hinge/boom/mass remained the same as in th=
e

past tests, with its 1/4" diameter stainless steel rod just laying across
the two
outer rods/bolts here. The test pendulum/mass offset here was reduced from
2"
to just a 1/4" offset and allowed to oscillate till it visually quit moving
as a test
of the friction/s involved. It visually oscillated 5 hours and 35 minutes,
which
was actually alot longer than I anticipated it would. This test result
suggests
that common bolt material can be adequately sufficient; and would of course
allow for replacing such with better material later, if one so wishes to do
so.

*** A good example of the "smooth" surface of a rod/s for a hinge, can be
noted in this example. I used acouple common grade steel .1375" diameter
rods, that "appeared" to be visually smooth, but with a likely coating of
zinc
or chrome plating thereon. I set the cross rod/boom/mass (.25" diameter rod=
)
thereon, and it oscillated less than 4 hours with a 1/4" mass deflection. I
then
smoothed them in a rotating drill press chuck for acouple minutes with a
strip
of 400 grit sandpaper. The same rods then were tested; and they then
allowed the cross rod to oscillate for 5 hours and 39 minutes. Finer grits
would
decrease the friction further. The sanding removed portions of the
zinc/chrome
coating/plateing on the rod...its color went to a more natural grayish/blac=
k
steel. Actually, the test was a double test; to see what two smaller
diameter
outer rods would do with a larger cross diameter rod...it didn't seem to
make
any noteworthy difference over using 1/4" diameter rods, as in the above
result.

The two bolt assembly could also be orientated to where its usefull for
other
seismometer hinges. For example, with the square metal rod flat on a
horizontal (to gravity) surface, and orientated to where the bolts are
coming
out a side; you have a S-G (vertical hanging pendulum) hinge. With the bolt=
s
pointing upward (or downward), and the longest square rod length is
horizontally placed against the imagined mast, you have a vertical hinge.
With
the square metal rod length upright, and the bolts coming out the side
view/s
(either left or right), you have a horizontal hinge. Most of what remains t=
o
do,
is to drill the square metal rod to where you can attach such to either the
mast
side, or the top of the mast for the seismometer type you want.

With a drill press, mounted drill press table vice, and with sawed off
square
rods, one could make quite a variety of lengths, or spaces inbetween the tw=
o
supported rods/bolts as desired. There is all kinds of more complicated way=
s
to make other similar two rod/bolt holding mechanisms around; but this has
to be the simplest. There is one limitation I'd consider, and that is to
only
use like 1/4" diameter rods/bolts or greater diameter, as the
weight/pressure
on them, may make lesser diameter bolts/rods bend or deflect abit, where
the ends (bolt heads) of such is not frame supported.

Take care, Meredith Lamb
Hi all,



Yesterday, I tried the simplest hinge (the two outer rod support/contacts) =
configuration

using the most commonly available material I could think of.  Its simp=
ly acouple of bolts

of a common 2.5" length, with 1/4" diameter, where only part of t=
he length (.750")

is threaded, and the rest of the length is of a round rod out to the hex sh=
aped bolt

head.  The threaded end is inserted or screwed into a piece of square =
metal rod. 

This leaves the smooth round exposed rod and of course the bolt head extend=
ed

outward with no bolt head support.  I used a rusty rectangular block o=
f steel that

already had two separated threaded holes, that matched the thread of the tw=
o bolts

for this test.  They were firmly screwed into the steel to where the t=
hread ends.

Another way of visualizing such, is to imagine a coat hangar on a wall with=
 its

base frame...but with only two extending rods/shafts thereon.  The onl=
y bolt surface

smoothing action I took was to mount the bolts in a drill press chuck, and =
sand

the round bolt surfaces with a 400 grit strip of sandpaper for acouple minu=
tes each.



For this test, the two rod hinge is orientated so it was for a S-G; or a ha=
nging

pendulum.  The actual crossed rod/hinge/boom/mass remained the same as=
 in the 

past tests, with its 1/4" diameter stainless steel rod just laying acr=
oss the two

outer rods/bolts here.  The test pendulum/mass offset here was reduced=
 from 2"

to just a 1/4" offset and allowed to oscillate till it visually quit m=
oving as a test

of the friction/s involved.  It visually oscillated 5 hours and 35 min=
utes, which

was actually alot longer than I anticipated it would.  This test resul=
t suggests

that common bolt material can be adequately sufficient; and would of course=


allow for replacing such with better material later, if one so wishes to do=
 so.



*** A good example of the "smooth" surface of a rod/s for a hinge=
, can be

noted in this example.  I used acouple common grade steel .1375" =
diameter

rods, that "appeared" to be visually smooth, but with a likely co=
ating of zinc

or chrome plating thereon.  I set the cross rod/boom/mass (.25" d=
iameter rod)

thereon, and it oscillated less than 4 hours with a 1/4" mass deflecti=
on.  I then

smoothed them in a rotating drill press chuck for acouple minutes with a st=
rip

of 400 grit sandpaper.  The same rods then were tested; and they then<=
br>
allowed the cross rod to oscillate for 5 hours and 39 minutes.  Finer =
grits would

decrease the friction further.  The sanding removed portions of the zi=
nc/chrome

coating/plateing on the rod...its color went to a more natural grayish/blac=
k

steel.  Actually, the test was a double test; to see what two smaller =
diameter

outer rods would do with a larger cross diameter rod...it didn't seem to ma=
ke

any noteworthy difference over using 1/4" diameter rods, as in the abo=
ve result.



The two bolt assembly could also be orientated to where its usefull for oth=
er

seismometer hinges.  For example, with the square metal rod flat on a =


horizontal (to gravity) surface, and orientated to where the bolts are comi=
ng

out a side; you have a S-G (vertical hanging pendulum) hinge.  With th=
e bolts

pointing upward (or downward), and the longest square rod length is

horizontally placed against the imagined mast, you have a vertical hinge.&n=
bsp; With

the square metal rod length upright, and the bolts coming out the side view=
/s

(either left or right), you have a horizontal hinge.  Most of what rem=
ains to do,

is to drill the square metal rod to where you can attach such to either the=
 mast

side, or the top of the mast for the seismometer type you want.



With a drill press, mounted drill press table vice, and with sawed off squa=
re

rods, one could make quite a variety of lengths, or spaces inbetween the tw=
o

supported rods/bolts as desired.  There is all kinds of more complicat=
ed ways

to make other similar two rod/bolt holding mechanisms around; but this has<=
br>
to be the simplest.  There is one limitation I'd consider, and that is=
 to only

use like 1/4" diameter rods/bolts or greater diameter, as the weight/p=
ressure

on them, may make lesser diameter bolts/rods bend or deflect abit, where
the ends (bolt heads) of such is not frame supported.



Take care, Meredith Lamb