Hi all,

This trial test involved resting a cross rod/boom/mass on the outer diamete=
r
rim mounting
support surfaces of two precision ball bearing assemblys. The ball bearings
assemblys were
5/8" in diameter, with a 1/4" bore/hole, and the width of the surface was
1/4". The finely
ground surface of such was getting close to a mirror finish, and was quite
"shiney" and reflective.
The bearings have a outer diameter shell of hardened steel; perhaps alittle
more brittle than
regular tool steels. Of course; like all bearing assemblys of this nature,
they contain round
ball bearings in the races therein.

The cross rod was the usual 1/4" diameter (~304 grade) stainless steel rod.
The surface
of which had only had 400 grit sandpaper smoothing, and is shiny but not
anywhere near,
to being a mirror reflective smooth rounded surface.

The cross rod simply rests atop the ball bearing assemblys (not inside), in
this vertical
hanging mass or S-G type pendulum test setup. The period of the mass
is 1.25seconds
and the weight is ~ 1.75 pounds. For this test, the ball bearings assemblys
were resting
atop two aluminum support structures, and anchored at the contact point
between the two,
with a glue.

The mass was offset 1/4" and allowed to oscillate freely, with no dampening
of the mass.
The time duration of the visual mass oscillations movement is a rough
indicator of the friction.

The first test was very encouraging for using these ball bearings assemblys
as the outer
two "rods" of the hinge, as the mass visually oscillated for 7 hours and 18
minutes, this
total time was the best I've seen in any test thus far. No oil was used to
lubricate the
contact points. If I can't visually see any oscillation from 2-3 feet
away...its "stopped"
as far as the timed oscillation test is concerned.

The second test used a drop of light oil at the contact junctions for
lubrication. That time
trial result was 7 hours and 3 minutes. Perhaps, if the seismometer is
operated in a
high humidity, or salt corrosive environment, it might be better to use jus=
t
alittle oil; to
avert any oxidation or rust effects. Stainless steel doesn't mean that it
can't rust; its just
more rust resistant than other steels.

Precision ball bearings assemblys come in a wide range of diameters, widths=
,
and bore
hole inside diameters. They are probably more commonly available than is th=
e
stainless
steel cross rod that I used here. Usually new assemblys can be quite
expensive. However
I note that E-Bay had some 20 items in various quanities that appeared very
cheap per
each item, and other larger assemblys were much more expensive. They likely
won't be
found in a common hardware store. Most bearings I've seen in hardware store=
s
recently
are crudely made units and won't begin to work here. It would be nice to us=
e
new ball
bearings assemblys as they are surface free of marks.

Old used precision ball bearings assemblys may have surface grime, or baked
on deposits,
but probably will work after cleaning. I would think a light hand
sanding/cleaning won't hurt
such, as they hardened steel to begin with. Salvaging bearings from old jun=
k
motors is
likely the most common "resource", but, they might be difficult to remove,
unless one uses
bearing puller tool mechanisms. Here, we don't care whether the bearing is
"shot", we use
the outer rim. The rim surfaces will never likely wear out, as the rod
simply rolls on its
surface.

I can't think of any reason why outer ball bearings assemblys wouldn't work
for other cross
rod hinges in any type of seismometer. They do allow for much greater
pressures, and mass
weights to be used.

Ball bearing assemblys with their center bore holes can be mounted rather
readily with
matching diameter bolts, on whatever type of orientation they could be used
for. One could
mount a washer slightly larger than the diameter of the ball bearing
assembly (but not
touching the cross rod), on the mounting bolt; which could be kind of a
safety stop. There
is likely a variety of mechanical ways to make assemblys with the two
rods/bearing surfaces
thereon.

The cross rod friction level can likely be reduced by sanding the rod in a
drill press or hand
drill with progressively finer grits of sandpaper, i.e., 400, 800, 1200,
etc., or using something
else smoother.

Take care, Meredith Lamb
Hi all,



This trial test involved resting a cross rod/boom/mass on the outer diamete=
r rim mounting 

support surfaces of two precision ball bearing assemblys.  The ball be=
arings assemblys were

5/8" in diameter, with a 1/4" bore/hole, and the width of the sur=
face was 1/4".  The finely 

ground surface of such was getting close to a mirror finish, and was quite =
"shiney" and reflective.

The bearings have a outer diameter shell of hardened steel; perhaps alittle=
 more brittle than

regular tool steels.  Of course; like all bearing assemblys of this na=
ture, they contain round

ball bearings in the races therein.



The cross rod was the usual 1/4" diameter (~304 grade) stainless steel=
 rod.  The surface

of which had only had 400 grit sandpaper smoothing, and is shiny but not an=
ywhere near,

to being a mirror reflective smooth rounded surface.



The cross rod simply rests atop the ball bearing assemblys (not inside), in=
 this vertical

hanging mass or S-G type pendulum test setup.  The period of the mass =
is 1.25 seconds

and the weight is ~ 1.75 pounds.  For this test, the ball bearings ass=
emblys were resting

atop two aluminum support structures, and anchored at the contact point bet=
ween the two,

with a glue.



The mass was offset 1/4" and allowed to oscillate freely, with no damp=
ening of the mass.

The time duration of the visual mass oscillations movement is a rough indic=
ator of the friction.



The first test was very encouraging for using these ball bearings assemblys=
 as the outer

two "rods" of the hinge, as the mass visually oscillated for  7 hours and 18 minutes, this

total time was the best I've seen in any test thus far.  No oil was us=
ed to lubricate the 

contact points.  If I can't visually see any oscillation from 2-3 feet=
 away...its "stopped"

as far as the timed oscillation test is concerned.



The second test used a drop of light oil at the contact junctions for lubri=
cation.  That time

trial result was 7 hours and 3 minutes.  Perhaps, if the seismometer i=
s operated in a

high humidity, or salt corrosive environment, it might be better to use jus=
t alittle oil; to

avert any oxidation or rust effects.  Stainless steel doesn't mean tha=
t it can't rust; its just

more rust resistant than other steels.



Precision ball bearings assemblys come in a wide range of diameters, widths=
, and bore

hole inside diameters.  They are probably more commonly available than=
 is the stainless

steel cross rod that I used here.  Usually new assemblys can be quite =
expensive.  However

I note that E-Bay had some 20 items in various quanities that appeared very=
 cheap per

each item, and other larger assemblys were much more expensive.  They =
likely won't be

found in a common hardware store.  Most bearings I've seen in hardware=
 stores recently

are crudely made units and won't begin to work here.  It would be nice=
 to use new ball

bearings assemblys as they are surface free of marks.  



Old used precision ball bearings  assemblys may have surface grime, or bake=
d on deposits,

but probably will work after cleaning.  I would think a light hand san=
ding/cleaning won't hurt

such, as they hardened steel to begin with.  Salvaging bearings from o=
ld junk motors is

likely the most common "resource", but, they might be difficult t=
o remove, unless one uses

bearing puller tool mechanisms.  Here, we don't care whether the beari=
ng is "shot", we use

the outer rim.  The rim surfaces will never likely wear out, as the ro=
d simply rolls on its

surface.



I can't think of any reason why outer ball bearings assemblys wouldn't work=
 for other cross

rod hinges in any type of seismometer.  They do allow for much greater=
 pressures, and mass

weights to be used.



Ball bearing assemblys with their center bore holes can be mounted rather r=
eadily with

matching diameter bolts, on whatever type of orientation they could be used=
 for.  One could

mount a washer slightly larger than the diameter of the ball bearing assemb=
ly (but not

touching the cross rod), on the mounting bolt; which could be kind of a saf=
ety stop.  There

is likely a variety of mechanical ways to make assemblys with the two rods/=
bearing surfaces

thereon.



The cross rod friction level can likely be reduced by sanding the rod in a =
drill press or hand

drill with progressively finer grits of sandpaper, i.e., 400, 800, 1200, et=
c., or using something

else smoother.



Take care, Meredith Lamb