In a message dated 22/10/05, KROBERTS23@............... writes:

>  Some of the home built vertical pendulums  use shims as a 
> hinge. I want to use shims as hinges for the horizontal pendulum. The shim 
> idea is to reduce friction and maximize the torque applied to the base/frame 
> by earth motion.  Although I have not been able to describe the design on 
> paper, I have been able to draw the plans. One (of many) problems: will the 
> shim material be strong enough to support the pendulum?  geoffry<><

Hi there Geoffrey,

       You try to use about 2 thou thick foil. Beryllium Copper, phosphor 
bronze, hard bronze and stainless steel are all satisfactory. Brass may be less 
satisfactory. Pure copper and Aluminum are not strong enough.
       Two types of foil hinge may be used, usually both in tension. The 
'Cardan' hinge is just vertical strips of foil clamped between two plates each 
side, maybe 1/16" to 1/8" apart. The crossed foil hinge joins the cut away 
corners of two square rods, see http://www.bryantlabs.net/seismo.html or 
http://www.eas.slu.edu/People/STMorrissey/index.html click on 'photos and report'. These 
particular hinges are for vertical seismometers, but the same principles apply 
to horizontal types.
        The 60 degree 'knife edges' used on chemical balances actually had a 
rounded edge - they were not actually 'sharp' - and they worked fine for light 
loads. Trying to use either a point in a cup or a metal cutting blade on a 
flat give huge contact forces and are likely to limit the performance of a 
seismometer, later if not immediatly.
       Have a look at http://www.jclahr.com/science/psn/cor_psn.html for a 
Lehman with single wire suspensions. 
       Regards,

       Chris Chapman
In a message=20=
dated 22/10/05, KROBERTS23@............... writes:



 Some of the home built ver=
tical pendulums  use shims as a=20

hinge. I want to use shims as hinges for the horizontal pendulum. The sh=
im=20

idea is to reduce friction and maximize the torque applied to the base/f=
rame=20

by earth motion.  Although I have not been able to describe the des=
ign on=20

paper, I have been able to draw the plans. One (of many) problems: will=20=
the=20

shim material be strong enough to support the pendulum?  geoffry<=
;><



Hi there Geoffrey,



       You try to use about 2 thou thick f=
oil. Beryllium Copper, phosphor bronze, hard bronze and stainless steel are=20=
all satisfactory. Brass may be less satisfactory. Pure copper and Aluminum a=
re not strong enough.

       Two types of foil hinge may be used=
, usually both in tension. The 'Cardan' hinge is just vertical strips of foi=
l clamped between two plates each side, maybe 1/16" to 1/8" apart. The cross=
ed foil hinge joins the cut away corners of two square rods, see http://www.=
bryantlabs.net/seismo.html or http://www.eas.slu.edu/People/STMorrissey/inde=
x.html click on 'photos and report'. These particular hinges are for vertica=
l seismometers, but the same principles apply to horizontal types.

        The 60 degree 'knife edges' u=
sed on chemical balances actually had a rounded edge - they were not actuall=
y 'sharp' - and they worked fine for light loads. Trying to use either a poi=
nt in a cup or a metal cutting blade on a flat give huge contact forces and=20=
are likely to limit the performance of a seismometer, later if not immediatl=
y.

       Have a look at http://www.jclahr.co=
m/science/psn/cor_psn.html for a Lehman with single wire suspensions.=20

       Regards,



       Chris Chapman