In a message dated 6/14/01 12:26:40 AM GMT Daylight Time, DSaum@............ writes: << 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. >> A low friction pivot is still a friction pivot!!! A friction-free pivot has been described consisting of a ring going around the lower pivot post with a spring wire under tension in back of the post. The spring stores energy and gives it back to provide a completely friction-free pivot. This is the ideal solution but requires machine-shop work you can't do at home on the kitchen table. I got around this problem by replacing the steel ring with a square wooden frame made from small pieces of poplar wood you can buy at the "Home Depot" home improvement stores or elsewhere. Use flathead wood screws to hold the wooden frame together. I made adjustable clamps for the spring wire from 3/8-inch square steel rod. With a hack saw cut two pieces 1 1/2-inch long and two pieces 1-inch long. Drill the ends of the long pieces to mount them with flathead wood screws on a wooden center pivot post and the square frame. The short pieces are the clamps and are mounted on the long pieces with two 10-32 socket-head cap screws that clamp them down on the spring wire. Loosen them slightly to make adjustments in the length of the spring wire to center and level the Boom on the now friction-free pivot point. The square steel rod, 10-32 socket-head screws and the 10-32 tap and tap drill plus a handle for the tap, are all found at Home Depot or other hardware stores. The music wire for the spring can be a steel guitar string from a music store. Use cutting oil on the tap and be gentle, backing out often to break the chips, so as not to jam the tap and break it. The big advantage of my spring wire clamps is they don't kink the wire as a set screw would do. Kinks would prevent precision adjustment. Have fun, Cap __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>