PSN-L Message - Subject: Re: New Seismo

dave.nelson@............... Subject: Re: New Seismo hi Chris Am really at the end of the rope here ... just total frustration... = spent all day=20 yesterday improving the period got down to 11 sec. set up a magnetic dampen= ing system with a strip of aluminium 1.5cm wide going in between the 2 magnets. The only thing that seems to achieve is dropping my period from 11 sec do= wn to=20 ~ 7 sec. It doesnt appear to do any actual dampening as the unit will jus= t go on=20 oscillating for ages and just slowly dying down on its own see...=20 http://www.sydneystormcity.com/screen%20dump.bmp Hi Dave, I can't see from your photo how the magnet is mounted to interact with = the Aluminium=20 blade, or what sort of magnet it is. Can you explain further, please ? What= thickness is=20 the aluminium sheet and is it soft Aluminium or hard Aluminium Alloy, pleas= e ? I use 1/16"=20 thick copper sheet, but you can use 1 mm thick sheet. Aluminium is weakly d= ia-magnetic.=20 The damper should NOT reduce the period ! This suggests that the magnet is = attracted to=20 something on the arm ? Look at the drawings of my damper system. IT WORKS JUST FINE !=20 See http://www.jclahr.com/science/psn/chapman/lehman/index.html=20 ****BTW I did take your bottom pivot advice. I have a flat steel plate on = the end of the=20 boom against the ball in the vertical Are the ball bearing AND the steel plate BOTH made of HARDENED Stainles= s Steel, please ? I use a medical Swann-Morton scalpel blade cut to a convenient length using= a Dremmel silicon=20 carbide cutting disk. Ordinary steel will rust and Austenitic stainless is = too soft --- if=20 you can file it, it is no good !=20 The reason that I am querying this, is that I can set the period of my L= ehman to 25 seconds=20 DEAD EASILY ! I have run it at a period of 60 seconds !=20 =20 ****maybe you can help further ? :) Does this help ? Let me know.=20 Regards,=20 Chris Chapman ****BTW I did take your bottom pivot advice. I have a flat steel plate on = the end of the=20 boom against the ball in the vertical Are the ball bearing AND the steel plate BOTH made of HARDENED Stainles= s Steel, please ? I use a medical Swann-Morton scalpel blade cut to a convenient length using= a Dremmel silicon=20 carbide cutting disk. Ordinary steel will rust and Austenitic stainless is = too soft --- if=20 you can file it, it is no good !=20 The reason that I am querying this, is that I can set the period of my L= ehman to 25 seconds=20 DEAD EASILY ! I have run it at a period of 60 seconds !=20 =20 ****maybe you can help further ? :) Does this help ? Let me know.=20 Regards,=20 Chris Chapman ****BTW I did take your bottom pivot advice. I have a flat steel plate on = the end of the=20 boom against the ball in the vertical Are the ball bearing AND the steel plate BOTH made of HARDENED Stainles= s Steel, please ? I use a medical Swann-Morton scalpel blade cut to a convenient length using= a Dremmel silicon=20 carbide cutting disk. Ordinary steel will rust and Austenitic stainless is = too soft --- if=20 you can file it, it is no good !=20 The reason that I am querying this, is that I can set the period of my L= ehman to 25 seconds=20 DEAD EASILY ! I have run it at a period of 60 seconds !=20 =20 ****maybe you can help further ? :) Does this help ? Let me know.=20 Regards,=20 Chris Chapman ****BTW I did take your bottom pivot advice. I have a flat steel plate on = the end of the=20 boom against the ball in the vertical Are the ball bearing AND the steel plate BOTH made of HARDENED Stainles= s Steel, please ? I use a medical Swann-Morton scalpel blade cut to a convenient length using= a Dremmel silicon=20 carbide cutting disk. Ordinary steel will rust and Austenitic stainless is = too soft --- if=20 you can file it, it is no good !=20 The reason that I am querying this, is that I can set the period of my L= ehman to 25 seconds=20 DEAD EASILY ! I have run it at a period of 60 seconds !=20 =20 ****maybe you can help further ? :) Does this help ? Let me know.=20 Regards,=20 Chris Chapman

= dave.nelson@........... om.au
Subject: Re: New Seismo

hi Chris Am really at the end of the rope here = .... just total frustration... spent all day yesterday improving the period got down to 11 sec. set up a magnetic dampen= ing system with a strip of aluminium 1.5cm wide going in between the 2 mag= nets. The only thing that seems to achieve is dropping my period from 11 s= ec down to ~ 7 sec. It doesnt appear to do any actual dampening as the uni= t will just go on

oscillating for ages and just slowly dying down on its own s= ee... http://www.sydneystormcity.com/screen%20dump.bmp Hi Dave,

I can't see from your photo how the magnet is m= ounted to interact with the Aluminium

blade, or what sort of magnet it is. Can you explain further, plea= se ? What thickness is

the aluminium sheet and is it soft Aluminium or hard Aluminium All= oy, please ? I use 1/16"

thick copper sheet, but you can use 1 mm thick sheet. Aluminium is= weakly dia-magnetic.

The damper should NOT reduce the period ! This suggests that the m= agnet is attracted to

something on the arm ?

Look at the drawings of my damper system. IT WO= RKS JUST FINE !

See http://www.jclahr.com/science/psn/chapman/lehm= an/index.html

= ****BTW I did take your bottom pivot advice. I have a flat steel plat= e on the end of the boom against the ball in the vertical

= Are the ball bearing AND the steel plate BOTH made o= f HARDENED Stainless Steel, please ?

= I use a medical Swann-Morton scalpel blade cut to a convenient len= gth using a Dremmel silicon

= carbide cutting disk. Ordinary steel will rust and Austenitic stainless= is too soft --- if

= you can file it, it is no good !

= The reason that I am querying this, is that I can set the = period of my Lehman to 25 seconds

= DEAD EASILY ! I have run it at a period of 60 seconds ! =

= ****maybe you can help further ? :)

= Does this help ? Let me know.

= Regards,

= Chris Chapman

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