> From: "Bryan&Regina Goss"
> Date: Tue, 12 Jun 2001 13:28:56 -0500 > > I have read that a ball bering was used in place of a knife edge >........http://www.1goss.com/seis.htm I read this also, so when I built my Lehman I used a ball bearing but I had trouble getting a smooth metal surface that it could rest against without making a dent. So I used a vertical piece of glass about the size of a microscope slide. It works very well as a low friction pivot. It would seem that the bearing would gradually work its way off the glass since there is nothing to center it, but this has not happened in months of operation. I suppose you could superglue a big washer to the glass to form a keeper for the bearing if you expect major motions near your unit. For my next Lehman I plan to build a shorter boom (now ~30") so the entire system can sit under an inexpensive 24" glass fish tank. I am tired of looking at the ugly cardboard box I use as an air motion shield now. Your plexiglass enclosure sure looks great, but expensive. I would also like to get rid of my oil damping because it is going to spill and cause a big mess one day. Right now I am working on a way of using a rare earth magnet assembly from a disk drive to do inexpensive and compact magnetic damping. These magnet assemblies are only a couple of $$. Maybe if the magnets are used in the paired assembly they do not have to be separated as far from the pickup coil as a horseshoe magnet does with it is used for magnetic damping. Dave The Inexpensive Seismometer Project http://www.infiltec.com/seismo/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>