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/brb.cfm) 
_http://www.smallparts.com/products/descriptions/BSP.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
 



   






In a message dated 07/06/2008, gel@................. writes:
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3D"Times New Roman" color=3D#=
000000=20
  size=3D3>Small Parts Inc. stocks carbide, synthetic ruby (red) and sapphir=
e=20
  (clear) balls that could probably replace (and very likely enhance the piv=
ot)=20
  of your steel ball bearings in your seismometer pivots.  

The=20
  corundum sizes range from 1/64" up to 1/8" @ $3.45 up to $4.00 each. =
 You=20
  can buy in
quanity somewhat cheaper.  The sphericity (roundness)=20
  listed is 0.000025".

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

The=20
  tungsten carbide balls range from 1/16" up to 1/2" @ $3.25 up to $16.80=20
  each.  They
have metric sizes also.  The sphericity listed is=
=20
  0.0006"...quite abit less round than the corundum.
=


Hi Meredith,
 
    Hardness is no the only criterion. You also=20
need high shear and compressive strengths to prevent chipping around th=
e=20
contact point. 1/8" OD ball is a bit small in my opinion for a ~2 kg axial l=
oad,=20
common on Lehmans. I would be happier with 3/8" ~ 1/2" OD. The surface needs=
 to=20
be highly polished. I doubt if a sphericity of 0.0006" is at all limiting.
 
    You also need hard polished flats for the beari=
ng=20
to roll on. What is available, please?
 
    With a 22" arm, I get a period >30 seconds q=
uite=20
easily with a 1/2" SS bearing ball and a SS flat cut from a scalpel blade gl=
ued=20
to the end of the Al arm.
 
    Regards,
 
    Chris Chapman