The first two Internet sites are not accessible ----- Original Message -----=20 From: meredith lamb=20 To: psn-l@................. Sent: Saturday, August 11, 2007 7:49 PM Subject: Crossed rod pivot on 2 HD flat surface inner ring/holes Hi all, Heres a quite different but very interesting and potentially useful surplus item that could have best use in a hanging mass (horizontal), i.e., a "S-G"; or, as part of a pivot hinge for a vertical seismometer. A strong incentive is that the item is likely obtained just about everywhere world wide at little cost...except for the rolling pivot rod axis used. They can be found normally as obsolete, as factory rejects, removed from equipment or even with damaged flat surfaces from read heads. This subject is in regard to discrete Hard Drive (HD) disks (sputtered or electroplated; with a mirror like finish, and NOT the older iron oxide reddish orange color disks) as part of a seismometer pivot hinge. See "normal" hard drive pictures and misc., details at: http://www.storagereview.com/guide2000/ref/hdd/op/ index.html Specifically, its the inner inside circular but flat mounting hole/ring that is part of the pivot. The inner hole/ring on disks I've seen is about 0.980" in diameter. For a horizontal (S-G),=20 a straight rod rests on the separated disks inner ring surfaces; and on the straight pivot rod is a shaft coupler with two setscrews. One setscrew is used to afix to the straight axis pivot rod, and the other selected length sawed off head, screw, is used to attach a boom/mass. One could also use two=20 shaft couplers and space them with a bracket; to which a boom is attached; or any number of ways of mechanical attachment or improvements thereof.=20 For a vertical its much the same type of hinge layout with a spring...somewhat like the Georgia Tech vertical, (it replaces the flexure pivot/hinge), see: http://quake.eas.gatech.edu/Instruments/LPVERTO.htm or, any number of varietys of mechanical layout, including a traditional mast type vertical. The actual "desktop edge" horizontal test model was made out of common material, and was only made to initially test its usefulness. For this model, the straight rod is 1/4" diameter 304 grade stainless steel, which was wiped and briefly lightly sanded to get a clean surface. Its length straightness was only tested to roll straight down a flat incline surface for a=20 short distance; without deviating in its travel course. Most of the pivot/hinge support material is 3/4" thick MDF (Micro Density Fiberboard), which is only glued directly onth the HD disk with the brand "Titebond III Wood Glue". The glue itself is waterproof and is usually strong enough to where with any=20 wood, or MDF, will usually be well enough bonded to where the wood or fiber will end up being torn at a different location=20 than at the joint. Its not a "real" super glue, but good enough for the test purpose; and is fairly commonly available in the USA. The boom was roughly 14" in length of aluminum spacers and with a brass tube. The mass is brass and=20 weighs about 2.25 pounds. The two disks used were less than 0.0315" thick for the contact surface...perhaps ~ 0.020" wide at the rod contact area. See: http://www.geocities.com/meredithlamb/HDpivot.html The two disks and MDF parts were aligned/glued together on a surface plate for the bottom disk contact points and were upright squared for contact with acouple "1-2-3" (1" x 2" x 3") machinist blocks on the surface plate. Alignment is critical. One might be able to use plate glass as the "surface plate", and use a carpenders square with clamps or similar devices for doing the same alignment procedure. Initial oscillation duration time tests were quite simple...but obviously not lab quality. The mass was displaced 1/16", without dampening and a visual oscillation check was done over time. The time result was about 2 and 1/2 hours of oscillation...really exceptionally long for a somewhat rough setup: and was quite encouraging to say the least, for its amazing lack of much friction at all, a most critical part of any seismometer hinge/pivot. A recorded duration would be much better; but it would have to be done for each pivot made. Of course a table top model isn't a very good place to test such a model; as its subject to tilt from house hold movement activity. As a rough comparison, I've made/used acouple one thousandth inch thick X 1/4" wide brass flexure hinges on the same size mass in a hanging mass horizontal, and got about 30 minutes of free oscillation with a initial displacement of the mass of 1/4". The period of the described setup is about 1 second. However with a displacement sensor; the actual recorded seismic signal phases can indeed be very much longer. Its a often overlooked aspect of hanging mass or S-G seismometers with a sensitive sensor. Another positive aspect is that they=20 require alot less base setscrew adjustments over time than other types of horizontals...as the mass is absolutely a zeroing reference to the earths gravity. One light displacement sensor is described at: http://jclahr.com/science/psn/chapman/photo_detect/index.html The specific hinge type is similar to a "crossed rod" hinge described by Chris Chapman on a past PSN email some time back. This is not a direct model of a crossed rod hinge as such; as the rod rolls on curved (relative to the direction of sensing) flat surfaces on the inner disk ring. It is possible that with enough mass weight the straight rod could actually be bending and rolling on the disks inner circle rounded chamfer. The curved rolling surface is most ideal for a "S-G", at least in its direction of oscillation (sensing direction), as its curved zeroing placement is more or less absolute once adjusted for...less any tilt from ground movement or the the normal causes experienced by any seismometer. A real problem with this type of hinge is that the rod axis can be displaced laterally to the ground reference accidentally. One idea might be to use opposing or same pole ring magnets mounted both on the rod and other frame mounted magnets in a opposing (North to North, or South to South pole) magnetic field to "fix" its tendency to wander over time. I've not tried such yet; but it sees like a fix, so too speak. The pivot rod would be ideally non-magnetic as also with any shaft couplers used. It is suggested that the spacing between any two disks be more than 3/4" if possible....especially on a vertical. The=20 wider the spacing the more stable it should become. I accidentally knocked the mass on its axis rod side (S-G), and it actually rocked back and forth with a 3/4" spacing for about half a minute. Such a hinge/pivot can actually have acouple varietys of mechanical setups. Outside of the description above, its quite possible to mount the disks on a square hollow boom, and have the straight rod affixed to two separate support masts...I would think it might then oscillate longer due to the diameter of the inside ring to the pivot straight rod. Going further in this possible approach; once could have a "Steel Works brand, 1" aluminum tube (square)", of a=20 chosen length, plug the bottom end, partially fill it with shotgun lead shot pellets (the mass), and afix any dampening copper or aluminum to the arrangement. The square tube would be oviously quite rigid which is desireable and more easier to add component on their flat surfaces. The "Steel Works" brand is found in most USA hardware or home improvement outlets like Home Depot or Lowes, at a reasonable price. These hard drive disks can obviously be found in defective computer hard drives, and if, one can tear them apart successfully. For another source, they be found fairly frequently at (getting rare) electronic surplus stores, in various sizes from ~1.5 to 3.5" in diameter. One needs two disks, or; its also possible to saw up one disk and use the two halves as part of the hinge. Their disk thickness can vary of course; I've seen 0.0315: and 0.050" thicknesses. The actual rod contact surface is less than the disk thickness with the machining chamfers done. Over the years, I've seen seen these items sell for between 10 and 25 cents each...a really cheap price for a part of a potentially really effective ground displacement sensing seismometer pivot/hinge. Unfortunately, I haven't been able to discern the actual plating material on the hard drives disks or their thicknesses. Most of the disks are a rigid aluminum alloy; with the=20 plating adding alittle stiffness. I think the hard metal=20 material could be a nickel metal plate, based solely from the greyish mirror finsish reflection color tint. The actual computer useage magnetic recording medium is probably measured in millionths of a inch thick; but I don't think this applys to the metal thickness on the aluminum disk itself. This is some thin copper plating inbetween the=20 aluminum and the possible nickel plating. If a reader has more knowledge of the plating layers, I would be interested to read of such. They are high precision machined pieces,=20 and as a whole are guite rigid for their thickness. I would suggest using either new drills or carbide drills to work any mounting holes, or other higher quality sharp tools.. as too much pressure with a worn drill can distort/bulge out the drilling area surface of the disk. Their is other possible seismometer uses for hard drive disks. They do have a thin copper plating that is accessible via careful sanding off of the top tough metal layer; which makes its possible for use as a capacitance plate sensor, using normal lead solder for lead wire attachment. One would need a 200 watt high heat soldering iron because of the aluminum heat sink mass cooling; but I've done that before successfully. Although small diameter, they be stacked for thickness and then used with various length metal spacers/standoffs=20 inbetween for use as a S-G (horizontal sensor) frame with having enough plates available. One could also use threaded rods and nuts as that would probably be a more convenient and more accurate adjusted leveling spacing in relation to the base plate used. There is probably many more good uses. Take care, Meredith Lamb =20 =20The first two Internet sites are not=20 accessible----- Original Message -----From:=20 meredith lambSent: Saturday, August 11, 2007 = 7:49=20 PMSubject: Crossed rod pivot on 2 = HD flat=20 surface inner ring/holesHi all,Heres a quite different but very interesting and = potentiallyuseful surplus item that could have best use in a hangingmass (horizontal), i.e., a "S-G"; or, as part of a pivothinge for a vertical seismometer. A strong incentive = isthat the item is likely obtained just about everywhere = worldwide at little cost...except for the rolling pivot rod axis = used.They can be found normally as obsolete, as factory rejects,removed from equipment or even with damaged flat surfacesfrom read heads.This subject is in regard to discrete Hard Drive (HD) disks(sputtered or electroplated; with a mirror like finish, andNOT the older iron oxide reddish orange color disks) as = partof a seismometer pivot hinge. See "normal" hard drive=20 picturesand misc., details at:Specifically, its the inner inside circular but flat = mountinghole/ring that is part of the pivot. The inner hole/ring on = disksI've seen is about 0.980" in diameter. For a horizontal = (S-G),=20a straight rod rests on the separated disks inner ring = surfaces;and on the straight pivot rod is a shaft coupler with twosetscrews. One setscrew is used to afix to the straight = axispivot rod, and the other selected length sawed off head, = screw,is used to attach a boom/mass. One could also use = twoshaft couplers and space them with a bracket; to which a = boomis attached; or any number of ways of mechanical attachmentor improvements thereof.For a vertical its much the same type of hinge layout with = aspring...somewhat like the Georgia Tech vertical, (it = replacesthe flexure pivot/hinge), see:or, any number of varietys of mechanical layout, including = atraditional mast type vertical.The actual "desktop edge" horizontal test model was made = outof common material, and was only made to initially test itsusefulness. For this model, the straight rod is 1/4" = diameter304 grade stainless steel, which was wiped and briefly = lightlysanded to get a clean surface. Its length straightness = wasonly tested to roll straight down a flat incline surface for=20 ashort distance; without deviating in its travel course. = Most=20 ofthe pivot/hinge support material is 3/4" thick MDF (MicroDensity Fiberboard), which is only glued directly onth the = HDdisk with the brand "Titebond III Wood Glue". The glue = itselfis waterproof and is usually strong enough to where with = anywood, or MDF, will usually be well enough bonded to = wherethe wood or fiber will end up being torn at a different=20 locationthan at the joint. Its not a "real" super glue, but good=20 enoughfor the test purpose; and is fairly commonly available in = theUSA. The boom was roughly 14" in length of aluminumspacers and with a brass tube. The mass is brass = andweighs about 2.25 pounds. The two disks used = were lessthan 0.0315" thick for the contact surface...perhaps ~ = 0.020"wide at the rod contact area. See:The two disks and MDF parts were aligned/glued together ona surface plate for the bottom disk contact points and wereupright squared for contact with acouple "1-2-3" (1" x 2" x = 3")machinist blocks on the surface plate. Alignment is = critical.One might be able to use plate glass as the "surface = plate",and use a carpenders square with clamps or similar = devicesfor doing the same alignment procedure.Initial oscillation duration time tests were quite = simple...butobviously not lab quality. The mass was displaced = 1/16",without dampening and a visual oscillation check was doneover time. The time result was about 2 and 1/2 hours = ofoscillation...really exceptionally long for a somewhat = roughsetup: and was quite encouraging to say the least, for itsamazing lack of much friction at all, a most critical part = ofany seismometer hinge/pivot. A recorded duration would = bemuch better; but it would have to be done for=20 each pivot made.Of course a table top model isn't a very good place to testsuch a model; as its subject to tilt from house hold = movementactivity. As a rough comparison, I've made/used acouple = onethousandth inch thick X 1/4" wide brass flexure hinges on = thesame size mass in a hanging mass horizontal, and got about30 minutes of free oscillation with a initial displacement = ofthe mass of 1/4".The period of the described setup is about 1 second. = Howeverwith a displacement sensor; the actual recorded seismicsignal phases can indeed be very much longer. Its a = oftenoverlooked aspect of hanging mass or S-G seismometerswith a sensitive sensor. Another positive aspect is that=20 theyrequire alot less base setscrew adjustments over time thanother types of horizontals...as the mass is absolutely azeroing reference to the earths gravity. One light=20 displacementsensor is described at:The specific hinge type is similar to a "crossed rod" hingedescribed by Chris Chapman on a past PSN email some timeback. This is not a direct model of a crossed rod = hinge as=20 such;as the rod rolls on curved (relative to the direction of = sensing)flat surfaces on the inner disk ring. It is possible that=20 withenough mass weight the straight rod could actually be = bendingand rolling on the disks inner circle rounded chamfer. = Thecurved rolling surface is most ideal for a "S-G", at least in = itsdirection of oscillation (sensing direction), as its curved = zeroingplacement is more or less absolute once adjusted for...lessany tilt from ground movement or the the normal causesexperienced by any seismometer.A real problem with this type of hinge is that the rod axis = canbe displaced laterally to the ground reference = accidentally. =20 Oneidea might be to use opposing or same pole ring magnetsmounted both on the rod and other frame mounted magnets ina opposing (North to North, or South to South pole) = magneticfield to "fix" its tendency to wander over time. I've not=20 triedsuch yet; but it sees like a fix, so too speak. The pivot = rodwould be ideally non-magnetic as also with any shaft = couplersused.It is suggested that the spacing between any two disks bemore than 3/4" if possible....especially on a vertical. =20 Thewider the spacing the more stable it should become. Iaccidentally knocked the mass on its axis rod side (S-G), = andit actually rocked back and forth with a 3/4" spacing for = abouthalf a minute.Such a hinge/pivot can actually have acouple varietys = ofmechanical setups. Outside of the description above, = itsquite possible to mount the disks on a square hollow boom,and have the straight rod affixed to two separate supportmasts...I would think it might then oscillate longer due tothe diameter of the inside ring to the pivot straight rod.Going further in this possible approach; once could have a"Steel Works brand, 1" aluminum tube (square)", of achosen length, plug the bottom end, partially fill it withshotgun lead shot pellets (the mass), and afix anydampening copper or aluminum to the arrangement. Thesquare tube would be oviously quite rigid which is = desireableand more easier to add component on their flat surfaces. = The"Steel Works" brand is found in most USA hardware or homeimprovement outlets like Home Depot or Lowes, at areasonable price.These hard drive disks can obviously be found in defectivecomputer hard drives, and if, one can tear them apartsuccessfully. For another source, they be found = fairlyfrequently at (getting rare) electronic surplus stores, invarious sizes from ~1.5 to 3.5" in diameter. One = needstwo disks, or; its also possible to saw up one disk and usethe two halves as part of the hinge. Their disk = thicknesscan vary of course; I've seen 0.0315: and 0.050" = thicknesses.The actual rod contact surface is less than the disk = thicknesswith the machining chamfers done. Over the years, I've = seenseen these items sell for between 10 and 25 cents each...areally cheap price for a part of a potentially really = effectiveground displacement sensing seismometer pivot/hinge.Unfortunately, I haven't been able to discern the actualplating material on the hard drives disks or their = thicknesses.Most of the disks are a rigid aluminum alloy; with theplating adding alittle stiffness. I think the hard metal =material could be a nickel metal plate, based solely fromthe greyish mirror finsish reflection color tint. The = actualcomputer useage magnetic recording medium is probablymeasured in millionths of a inch thick; but I don't thinkthis applys to the metal thickness on the aluminum diskitself. This is some thin copper plating inbetween = thealuminum and the possible nickel plating. If a reader = hasmore knowledge of the plating layers, I would be interestedto read of such. They are high precision machined=20 pieces,and as a whole are guite rigid for their thickness. I = wouldsuggest using either new drills or carbide drills to workany mounting holes, or other higher quality sharp tools..as too much pressure with a worn drill can distort/bulge = outthe drilling area surface of the disk.Their is other possible seismometer uses for hard drive = disks.They do have a thin copper plating that is accessible viacareful sanding off of the top tough metal layer; which = makesits possible for use as a capacitance plate sensor, usingnormal lead solder for lead wire attachment. One would = needa 200 watt high heat soldering iron because of the aluminumheat sink mass cooling; but I've done that before = successfully.Although small diameter, they be stacked for thickness andthen used with various length metal spacers/standoffsinbetween for use as a S-G (horizontal sensor) frame withhaving enough plates available. One could also usethreaded rods and nuts as that would probably be a moreconvenient and more accurate adjusted leveling spacing inrelation to the base plate used. There is probably = manymore good uses.Take care, Meredith Lamb