Ringing piers

[pwalsh61]

In another topic I saw a link to (and watched) a video which, to be honest, seemed more like an advertisement than an objective assessment of the construction of piers. One of the topics to consider was the resonance of the pier, or how much vibration was likely to be imparted to the scope should something hit the pier. This set me thinking. In years gone by I dabbled in a bit of railway modelling and one of the books in my collection is "An Approack to Building Finescale Track" by Iain Rice.

Now, you might be wondering what this has to do with piers etc. Well, in the book, Iain tackles the problems of baseboard noise. His solution is to use techniques in the audio industry. If my memory serves me well, this involves "Acoustic decoupling" involving materials of different densities so, for example, you would have the timber baseframe, an MDF sub-frame, a layer of fairly dense foam (such as used in camping mats/garden kneelers) then another MDF subframe. The foam would absorb much of the vibrations caused by model stock trundling along.

Now, I'm not necessarily suggesting pier tops are made of foam, as that would be pretty daft. However, I was wondering if some form of dense foam could be used between mount and top of pier. The key thing, I think, is the use of a material of different density which can absorb vibrations caused by something striking the pier, perhaps introducing foam/neoprene "washers" on the bolts attaching head to pier so that there isn't a metal on metal link through which vibrations could travel.

Useful idea, or am I talking out the top of my head?

[Paulus17]

Does the pier get hit that often when imaging/viewing anyway??

[pwalsh61]

I would imagine not, but I can also see how annoying it might be if a sub is ruined as a result of vibrations - especially if there's a long, nulti-minute exposure involved. Given the state of the weather in recent months imagers need to take advantage of every photon their sensor collects

[Daniel-K]

my pier is filled with concrete " SOLID! " just paint it with glow in the dark paint and you wont bump into it

[fwm891]

The idea is to fill a hollow pier with sand, the sand absorbing the vibrations from the tube wall.

[Gina]

Does the pier get hit that often when imaging/viewing anyway??

Mine doesn't but I did do a test. I set the scope pointing at a bright star and watched it's image in EOS Utilities live view. Then I hit my concrete pier - not a wobble.

[ollypenrice]

After watching the video I'd venture to suggest that hot air around the pier would be more of a problem than resonating steel...

Olly

[pwalsh61]

Lol. Ahh but wouldn't that cause a temperature differential between different metals used? ;-)

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[Bizibilder]

To prevent resonance in a metal pier it is usual to fit what look like "bracing" to the outside of the pier - usually a few strips of steel welded up the pier often in a three or four vaned pattern. These (although some would have you believe otherwise) do not add much, if anything, to the "strength" of the pier but they do effectivly upset any resonances within the pier especially if they are not welded at any precise fraction of the piers height (ie not welded 1/2 or 1/3 etc of the way up the pier).

This is harmonic damping and the best analogy is a guitar string. Pluck it and you get one note, put down the 12th fret (1/2 way) and you get the first harmonic of the original note etc etc. The pier is just like the string, upset those harmonics and it ruins any resonances within the pier and effectivly dampens them out quickly. Filling the pier tube with sand or clay etc has the same helpful effect. Hope this helps.