PSN-L Email List Message

Subject: Re: Flexures, Hinges and Periods
From: ChrisAtUpw@.......
Date: Wed, 1 Aug 2007 22:56:10 EDT


In a message dated 2007/08/01, tchannel1@............ writes:

> My question is where should I set the period for the best overall results? 
> Or is it just a personal preference?

Hi Ted,

       The P and S waves come in from 10 Hz down for locals, down to 2 to 0.5 
Hz for teleseismic. The ocean microseisms, which you usually want to avoid, 
come in usually 4~7 seconds, but they may be up to ~12 secs. The Love and 
Rayleigh waves often come in at about 20 seconds, but they may be more than factors 
of 2 on either side. Download and read http://psn.quake.net/info/analysis.pdf 
?

> My second question has to do with testing the resistance or friction of 
> various hinges.
> I have seen razor blades, roller on roller, wires, figure 8 wires, foil and 
> so on.....Has anyone tested or qualified the different using one or more of 
> these methods?

       Yes. There are several notes on psn about this.

       Knife blades, razor blades and points tend to fail easily and are 
likely to give problems / not last long / severely restrict the period obtainable. 


       The ''knife edges'' used in chemical balances are actually 60 deg 
triangular rods with slightly rounded edges and are OK for loads up to 200 gm.

       The usual order for flexures / hinges is single wires, single foils, 
crossed wires and foils, ball on a plane, crossed cylinders and rolling wires 
or foils, in that order. This assumes that the load ratings are ~comparable. 
You need very rigid and massive mountings to test pendulum run down times, 
otherwise the mounting absorbs some of the motion energy. Note that lightly damped 
pendulum run down times do NOT follow the simple harmonic oscillator type of 
decay. There is more than a factor of 4 between the best and the worst. Balls, 
planes and cylinders should all be of hardened material, eg SS / WC ball 
bearings. When I say massive mountings, the NBS were getting 1 kg 2 second clock 
pendulums synchronising when mounted on a large concrete seismic plinth weighing 
several tens of tons. They eventually had to mount the pendulums at right 
angles to prevent this..... 

> I did a simple test, using various hinges, foil, wire, razor blades and 
> eyebolts.  I could and did see some difference in how long a pendulum would 
> swing free.  I just moved the pendulum 6" and let it go counted the cycles until 
> it stopped.
> Not very accurate, but I could see only about 20 percent different, between 
> what I would call good and better hinges.
> I am not suggesting this test tell the whole story.  So if there is a study 
> I would like to see it or hear about your own testing.  I was surprised there 
> was not a greater different on my test.

       I don't think that you can get eyebolts in a really hard corrosion 
resistant metal? You might be able to get EN56 SS washers? You can get type 416 
shoulder bolts from www.mcmaster.com. You can buy martensitic chrome steel rod 
and also tungsten carbide rod. Austenitic SS is generally too soft. You can 
stick a SS razor or knife blade to other metals as a counterface for SS / 
carbide ball bearings. Use two component acrylic adhesive. BIC pens use 1 mm 
tungsten carbide balls, but you are limited by the load that the counterface will 
take. You can buy flat WC triangular tool tips for lathes. You can buy WC needle 
rollers, but if you want SS, you have to cut, harden and polish them yourself. 
You can buy solid WC drills in various sizes and use the shank end. I haven't 
tried tool steel, but it should be OK and it is another 'alternative' in 
square and round rod forms. You will probably need to grind / lapp and polish it. 
These dry rolling contacts need to be both very hard and highly corrosion 
resistant, or they won't last long. They also need to be protected from dust and 
dirt eg. with concentric paper / plastic tubes. 

       Not all foil and wire flex materials ''are equal'', due to anelastic 
internal friction. Brass is poor. Bronze, phosphor bronze, some SS and Niobium 
are good. Carbon steel shim probably won't last long unless you pickle it and 
varnish / paint it, or Nickel plate it. You can buy Nickel plated piano wire 
(for Mandolins) from D'Addario down to 8 thou. As far as I know, the piano wire 
from Smallparts is NOT Ni plated, but do check?

       Hope that this gives you a rough idea of some practical 
considerations.

       Regards,

       Chris Chapman   
In a me=
ssage dated 2007/08/01, tchannel1@............ writes:

My question is where should I s= et the period for the best overall results? Or is it just a personal prefere= nce?


Hi Ted,

       The P and S waves come in from 10 Hz do= wn for locals, down to 2 to 0.5 Hz for teleseismic. The ocean microseisms, w= hich you usually want to avoid, come in usually 4~7 seconds, but they may be= up to ~12 secs. The Love and Rayleigh waves often come in at about 20 secon= ds, but they may be more than factors of 2 on either side. Download and read= http://psn.quake.net/info/analysis.pdf ?


My second question has to do w= ith testing the resistance or friction of various hinges.
I have seen razor blades, roller on roller, wires, figure 8 wires, foil and= so on.....Has anyone tested or qualified the different using one or more of= these methods?


       Yes. There are several notes on psn ab= out this.

       Knife blades, razor blades and points t= end to fail easily and are likely to give problems / not last long / severel= y restrict the period obtainable.

       The ''knife edges'' used in chemical ba= lances are actually 60 deg triangular rods with slightly rounded edges and a= re OK for loads up to 200 gm.

       The usual order for flexures / hinges i= s single wires, single foils, crossed wires and foils, ball on a plane, cros= sed cylinders and rolling wires or foils, in that order. This assumes that t= he load ratings are ~comparable. You need very rigid and massive mountings t= o test pendulum run down times, otherwise the mounting absorbs some of the m= otion energy. Note that lightly damped pendulum run down times do NOT follow= the simple harmonic oscillator type of decay. There is more than a factor o= f 4 between the best and the worst. Balls, planes and cylinders should all b= e of hardened material, eg SS / WC ball bearings. When I say massive mountin= gs, the NBS were getting 1 kg 2 second clock pendulums synchronising when mo= unted on a large concrete seismic plinth weighing several tens of tons. They= eventually had to mount the pendulums at right angles to prevent this.....=20=


I did a simple test, using var= ious hinges, foil, wire, razor blades and eyebolts.  I could and did se= e some difference in how long a pendulum would swing free.  I just move= d the pendulum 6" and let it go counted the cycles until it stopped.<= FONT COLOR=3D"#000000" BACK=3D"#ffffff" style=3D"BACKGROUND-COLOR: #ffffff"= SIZE=3D3 PTSIZE=3D12 FAMILY=3D"SANSSERIF" FACE=3D"Arial" LANG=3D"0">
Not very accurate, but I could see only about 20 percent different, between= what I would call good and better hinges.
I am not suggesting this test tell the whole story.  So if there is a=20= study I would like to see it or hear about your own testing.  I was sur= prised there was not a greater different on my test.


       I don't think that you can get eyebolts= in a really hard corrosion resistant metal? You might be able to get= EN56 SS washers? You can get type 416 shoulder bolts from www.mcmaster.com.= You can buy martensitic chrome steel rod and also tungsten carbide rod. Aus= tenitic SS is generally too soft. You can stick a SS razor or knife blade to= other metals as a counterface for SS / carbide ball bearings. Use two compo= nent acrylic adhesive. BIC pens use 1 mm tungsten carbide balls, but you are= limited by the load that the counterface will take. You can buy flat WC tri= angular tool tips for lathes. You can buy WC needle rollers, but if you want= SS, you have to cut, harden and polish them yourself. You can buy solid WC=20= drills in various sizes and use the shank end. I haven't tried tool steel, b= ut it should be OK and it is another 'alternative' in square and round rod f= orms. You will probably need to grind / lapp and polish it. These dry rollin= g contacts need to be both very hard and highly corrosion resistant, or they= won't last long. They also need to be protected from dust and dirt eg. with= concentric paper / plastic tubes.

       Not all foil and wire flex materials ''= are equal'', due to anelastic internal friction. Brass is poor. Bronze, phos= phor bronze, some SS and Niobium are good. Carbon steel shim probably won't=20= last long unless you pickle it and varnish / paint it, or Nickel plate it. Y= ou can buy Nickel plated piano wire (for Mandolins) from D'Addario down to 8= thou. As far as I know, the piano wire from Smallparts is NOT Ni plated, bu= t do check?

       Hope that this gives you a rough idea o= f some practical considerations.

       Regards,

       Chris Chapman

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