PSN-L Email List Message

Subject: Re: Lehman
From: CapAAVSO@.......
Date: Thu, 14 Jun 2001 10:01:42 EDT

In a message dated 6/14/01 12:26:40 AM GMT Daylight Time, DSaum@............ 

<< 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,

Public Seismic Network Mailing List (PSN-L)

[ Top ] [ Back ] [ Home Page ]

Larry Cochrane <cochrane@..............>