Chirs Chapman,

 Thanks for the link to the ball bearings, I have them on the way.
I am going to do a total rebuild. I have in hand ½ square aluminium, will this be ok for the boom. If it is not I will buy the ½ nominal stainless steel water pipe you sugested.
I also ordered 12*18*¼ inch aluminum plate for the base.
If I use a boom length of 30 inches where should I put the weight I will try to attach the support wire the way you sugested as well. It will take me some time but I want the best seismograph I can build.
Thanks for all your help it will be used I have printed the emails out to refer to during construction.
Bryan S Goss
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