Hi Chris,

Good point on the small size corrundum balls and possible damaging heavy
mass on Lehmans...you're likely right there.
Most horizontal seismos I've seen on various web photos don't appear to have
much mass weight....perhaps
they could work OK for masses of less than ~ 1 pound.

I think the Sprengnether horizontal offset wire pivot approach for heavy
mass Lehmans is superior in every way to use.
and one doesn't have any of the technical problems with balls and contacts
fuss.  (Hey...its Saturday night live...ha)

The ball bearings email is just a note on such....as far as a asked for
flats reference for such, I think
you references in past emails has most likely covered it all.

I think I might try the smoother surface corrundum balls on a light mass S-G
hanging mass, sometime in the future; to
just check them out.  I've tried various size used/new ball bearings in a
table top S-G tests in the past,
and wasn't at all encouraged by their repetitive "sticking" results for less
than (1/16") ~ 2 pound mass offsets.

S-G's are the horizontal future.  (Its still Saturday night live...ha).

Take care, Meredith




On Sat, Jun 7, 2008 at 2:02 PM,  wrote:

>  In a message dated 07/06/2008, gel@................. writes:
>
> Small Parts Inc. stocks carbide, synthetic ruby (red) and sapphire (clear)
> balls that could probably replace (and very likely enhance the pivot) of
> your steel ball bearings in your seismometer pivots.
>
> The corundum sizes range from 1/64" up to 1/8" @ $3.45 up to $4.00 each.
> You can buy in
> quanity somewhat cheaper.  The sphericity (roundness) listed is 0.000025".
>
> http://www.smallparts.com/products/descriptions/brb.cfm
> http://www.smallparts.com/products/descriptions/BSP.cfm
>
> The tungsten carbide balls range from 1/16" up to 1/2" @ $3.25 up to $16.80
> each.  They
> have metric sizes also.  The sphericity listed is 0.0006"...quite abit less
> round than the corundum.
>
>  Hi Meredith,
>
>     Hardness is no the only criterion. You also need high shear and
> compressive strengths to prevent chipping around the contact point. 1/8" OD
> ball is a bit small in my opinion for a ~2 kg axial load, common on Lehmans.
> I would be happier with 3/8" ~ 1/2" OD. The surface needs to be highly
> polished. I doubt if a sphericity of 0.0006" is at all limiting.
>
>     You also need hard polished flats for the bearing to roll on. What is
> available, please?
>
>     With a 22" arm, I get a period >30 seconds quite easily with a 1/2" SS
> bearing ball and a SS flat cut from a scalpel blade glued to the end of the
> Al arm.
>
>     Regards,
>
>     Chris Chapman
>
>
Hi Chris,

Good point on the small size corrundum balls and possible damaging heavy mass on Lehmans...you're likely right there.
Most horizontal seismos I've seen on various web photos don't appear to have much mass weight....perhaps

they could work OK for masses of less than ~ 1 pound. 

I think the Sprengnether horizontal offset wire pivot approach for heavy mass Lehmans is superior in every way to use.
and one doesn't have any of the technical problems with balls and contacts fuss.   (Hey...its Saturday night live...ha)


The ball bearings email is just a note on such....as far as a asked for flats reference for such, I think
you references in past emails has most likely covered it all.

I think I might try the smoother surface corrundum balls on a light mass S-G hanging mass, sometime in the future; to

just check them out.  I've tried various size used/new ball bearings in a table top S-G tests in the past,
and wasn't at all encouraged by their repetitive "sticking" results for less than (1/16") ~ 2 pound mass offsets.


S-G's are the horizontal future.  (Its still Saturday night live...ha).

Take care, Meredith

       

 
On Sat, Jun 7, 2008 at 2:02 PM,  <ChrisAtUpw@.......> wrote:







In a message dated 07/06/2008, gel@................. writes:
Small Parts Inc. stocks carbide, synthetic ruby (red) and sapphire 
  (clear) balls that could probably replace (and very likely enhance the pivot) 
  of your steel ball bearings in your seismometer pivots.  

The 
  corundum sizes range from 1/64" up to 1/8" @ $3.45 up to $4.00 each.  You 
  can buy in
quanity somewhat cheaper.  The sphericity (roundness) 
  listed is 0.000025".

http://www.smallparts.com/products/descriptions/brb.cfm

http://www.smallparts.com/products/descriptions/BSP.cfm

The 
  tungsten carbide balls range from 1/16" up to 1/2" @ $3.25 up to $16.80 
  each.  They
have metric sizes also.  The sphericity listed is 
  0.0006"...quite abit less round than the corundum.


Hi Meredith,
 
    Hardness is no the only criterion. You also 
need high shear and compressive strengths to prevent chipping around the 
contact point. 1/8" OD ball is a bit small in my opinion for a ~2 kg axial load, 
common on Lehmans. I would be happier with 3/8" ~ 1/2" OD. The surface needs to 
be highly polished. I doubt if a sphericity of 0.0006" is at all limiting.
 
    You also need hard polished flats for the bearing 
to roll on. What is available, please?
 
    With a 22" arm, I get a period >30 seconds quite 
easily with a 1/2" SS bearing ball and a SS flat cut from a scalpel blade glued 
to the end of the Al arm.
 
    Regards,
 
    Chris Chapman