Hi all In optical mounts, such as those for the mirrors in an ion laser, there are some refinements which may be of some use in this application. The laser application has similar or greater requirements for accuracy and stability. The principle difference is that the levelling is done between two pieces that are structural to the instrument, and that these two pieces are held in tight coupling to each other. At each of the three mounting points the two plates are held together by suitably strong springs, and pulled apart by the adjusting screws. In general one point is more or less fixed, while the other two points provide adjustment in the x and y dimensions. It would seem natural to put the fixed point under the mast of a lehman. An arrangement of this type would allow the bottom plate to the screwed firmly to whatever surface the instrument is meant to be measuring, and the rest of the instrument adjusted relative to this. a further refinement observable on laser mirror mounts are physical restraints preventing the moveable plate from being displaced by gross shocks. a screw with a waskher and a spacer under it's head through a clearance hole in the adjustable plate, screwed firmly into the base plate is common. The springs are usually mounted to bars set in grooves across holes in both plates. The bearing points are usually ball headed. The fixed point is commonly a ball bearing set over holes in each plate. A well engineered arrangement such as this provides excellent coupling between the instrument and the substrate, as well as fine and repeatable adjustments. and it should stay very firmly put in even a very large shake. I hope this is understandable and helpful. Happy New Year everyone Mark __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>