5 replies to this topic

[urbanMark]

I have an aluminum portable pier (10" dia, 0.090" wall thickness) and I'm considering spraying expanding foam inside the tube to deaden vibrations. Has anyone tried this? Other ideas for damping the tube without adding significant weight?

 

BTW - the vibration isn't horrible, but it could be better.

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[pyrasanth]

I would be cautious with this approach. If it does not work then your probably out of options as it would be very difficult to remove the foam & try something else. Personally I would not do this. Sand has always worked well as a dampening medium and it can be removed if the need arises. I don't think you will get better within the scope of a media that can be replaced.

 

If you want to try this then a better approach would be to see if you can reach the inside of the tube and insert a hollow column and fill that with foam- you then stand a chance of removal of the whole column if things don't work out.

Edited by pyrasanth, 06 July 2025 - 04:24 AM.

[afd33]

I would be cautious with this approach. If it does not work then your probably out of options as it would be very difficult to remove the foam & try something else. Personally I would not do this. Sand has always worked well as a dampening medium and it can be removed if the need arises. I don't think you will get better within the scope of a media that can be replaced.

If you want to try this then a better approach would be to see if you can reach the inside of the tube and insert a hollow column and fill that with foam- you then stand a chance of removal of the whole column if things don't work out.

The problem with sand is it makes his portable pier much less portable.

[macdonjh]

Neither sand nor foam will reduce the amplitude of the vibrations, only change the frequency of those vibrations.  The frequency does not matter.  The goal of your foundation is to limit the deflection of your pier, either due to external forces or vibration, to less than the image scale of your imaging gear.  See what you can do to couple your portable pier more solidly to the ground: set up on concrete, add sandbags to the legs/ on top of the leveling screws, don't walk around your gear when capturing, set up where there isn't truck or railroad traffic, etc. 

[Eddgie]

It appears to me that the telescope feet are on the ground. If it is not, skip to the end.

 

If you have ever noticed the ground vibrating when a heavy truck goes by, this tells you that the ground is not at all "solid." The ground is a mix of materials and pore spaces filled with air and water. It is "Spongy" and small contact patches may not be well supported. 

 

As a test, try setting the scope up on a concrete driveway or sidewalk and see if there is any improvement. If there is, then you may  want to consider putting down a concrete pad, or pour some concrete posts into the soil.

 

The end:  Consider some struts made of angle iron or some cable stays. 

Edited by Eddgie, 06 July 2025 - 12:31 PM.

[urbanMark]

Thanks everyone!

 

The ground is compacted decomposed granite in the pic above, and jumping or walking in the area has no impact on viewing. What I noticed was manual slewing to center an object caused a shake when the slew stops. Tapping near the top of the pier causes a similar shake (more so than my heavy duty tripod, but the tripod is not ideal with a long refractor). Obviously a concrete filled pier would be the gold standard here, but that's not portable. I'm just wondering if there is anything I can do improve this setup while remaining portable. 

 

BTW - tapping near the bottom of the pier does nothing, so I don't think sandbags on the legs would have any impact. The issue appears to be vibration of the main tube, which is unfortunately only 0.090" thick. 

 

I should add, I'm planning to mount larger scopes and even some dual scope setups, so while the above may sound like "nit picking", I want to avoid the problem getting worse with larger setups.

 

I did see a post where someone said they filled their hollow metal pier with expanding foam and it helped, but I can't find it now. Expanding foam is a mess to clean out, so I want to make darn sure it's going to do what I want before going down that path. 

 

Thanks!

Mark