[PeterM]

This is a very interesting thread. Thanks to all of you for the informative posts.
In my case I am doing multiple short movement, scripted slews to many galaxies for 25 second exposures with an alt az mounted 12inch LX200, I allow an 8 second damping time once I arrive at the object. I was using a 850mm high homemade pier of 165mm od with no gussets and dampening seemed quite ok. I have recently bought a Pegasus Pier as replacement (basically bought on looks, construction quality AND that it has the gussets). I can't give a report yet as only went in on the weekend and skies are crap, but will do as a comparison to what I had, don't know what value that will be given my needs over say those doing longer exposures.
After reading carefully the above I am not sure if we are comparing apples with apples here when it comes to steel piers, that is a section of pipe with plates welded top and bottom versus one with gussets (as I originally had).
Rally notes that the deflection on a pier example of 1000mm high /165 od /6.5mm wall as about say 1 arc sec (2.5kg lateral load) and notes this is without gussets (again, pretty much what I had).
As an example all the Pegasus piers I have seen (and most others I have seen) are gusseted (4 top and bottom, extending to about 50mm across the bottom 12mm plate and about 140mm high and about 6mm thick) with substantial welding, so in order to compare apples with apples does anyone know what affect does this have on lessening deflection as compared to a pier with no gussets? ie does it effectively act as an increase in the tube diameter (footprint at ground where the major issue is) and how would this be taken into account in measuring deflection?

PS where's Mark Bolton when you need him, he teaches this stuff.

Thanks

PeterM.