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Choosing a pier?

FLO

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FLO

FLO

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In a nutshell, it rang like a blumming bell, and I had to pack the girder recesses with concrete. I was using synchronous motors, and the frequency did transmit it's oscillations to the mount.

I remember hearing that a while ago, perhaps it was one of your posts. I think the conclusion was that a circular pipe was better than section.

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RobH

RobH

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Here's my pier Steve.

It has an aluminium plate that fits on top which was originally drilled out for an AP1200. I had a meade wedge at the time so redrilled for that, and later drilled it again for a CGE adapter.

Now I've got an AP1200, the original holes are used.

Levelling was done from the base, and I made a jig for the 16mm SS threaded rods to correctly position them into the concrete block. Unfortunately, one of them got somewhat out of line so it didn't fit.

This meant that I had to spend a day with a small hand file enlarging the 16mm holes in the 1 inch thick steel base...character building :)

The pier ended up with about 3 inches of rod under it, and this was prone to vibration (I couldn't get it any lower due to the dodgy rod).

I did try to get the pier down further by foolishly hitting the base with a lump hammer.....enclosed observatory, empty steel pier.....my head took a year to stop ringing :)

I've solved this problem by putting several 1 inch diameter homemade screw jacks under it and there is now no movement at all.

Cheers

Rob

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barkis

barkis

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Here's my pier Steve.

It has an aluminium plate that fits on top which was originally drilled out for an AP1200. I had a meade wedge at the time so redrilled for that, and later drilled it again for a CGE adapter.

Now I've got an AP1200, the original holes are used.

Levelling was done from the base, and I made a jig for the 16mm SS threaded rods to correctly position them into the concrete block. Unfortunately, one of them got somewhat out of line so it didn't fit.

This meant that I had to spend a day with a small hand file enlarging the 16mm holes in the 1 inch thick steel base...character building :)

The pier ended up with about 3 inches of rod under it, and this was prone to vibration (I couldn't get it any lower due to the dodgy rod).

I did try to get the pier down further by foolishly hitting the base with a lump hammer.....enclosed observatory, empty steel pier.....my head took a year to stop ringing ;)

I've solved this problem by putting several 1 inch diameter homemade screw jacks under it and there is now no movement at all.

Cheers

Rob

Did you intend to post an Image Rob?

Ron.B) Sorry mate, of course you have.:)

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FLO

FLO

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Thanks for the picture Rob :)

I can see why you say put the adjustment mechanism at the top! I think I'd rather it was bolted directly to the concrete rather than balanced on four threaded bars!

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RobH

RobH

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Absolutely Steve....I started with my big 14 inch Meade on top.

You wouldn't have thought that there would be any appreciable movement in 3 inches of 16mm rod, but that isn't the case at all :)

My pier was made by a chap who built one for himself, and also built mine, so I bought it like this. At the time, I had no experience at all, but learned as I went along.

Still, now it's properly braced, it works very nicely, although if I ever want to move it, and angle grinder will be the order of the day!

Cheers

Rob

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MartinB

MartinB

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An article here on steel piers Steve http://home.att.net/~dpersyk/Pier_Design.doc

If you go on any observatory board or forum you will find lots of heated debate about vibration and whether filling with sand makes any difference or not. From what I can gather, the high frequency vibrations that are damped with sand aren't the problem and that it much lower frequency stuff which can be an issue and this isn't addressed with sand. AE have their base slightly off flat so that tensioning the bolts applies a twist which they feel suppresses vibrations, I don't know whether this works or not or how much vibrations are an issue.

I've gone for a 6" Epsilon pier, they are also making me an EM200 adaptor. This should be an adequate diameter, I didn't want it too wide since I want to be able to get as far past the meridian as possible.

It seems that everyone has their own ideas but not much objective evidence to support them, other than the article above which only really addresses flex issues and dismisses vibration. All the pier manufacturers will cite the benefits of their engineering solutions.

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RobH

RobH

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I initially just filled mine with sand Martin, and it didn't do much to stop the HF vibrations, which is why I decided that I needed permanent contact between the damping material and the pier, and added the oil.

There is now no HF vibration at all.

Having been in audio for 30 years, and been involved in the construction of a few recording studios, I learned quite a lot about resonances and vibration...not much of it was theoretical, but a lot of practical stuff :)

Cheers

Rob

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FLO

FLO

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Thank-you for the article Martin :)

.... most steel piers with a plate on the bottom are slightly off flat, it's the welding. Fast thinking there though!

I used to be a welder (steel boat). When you weld, the metal expands then contracts towards the weld. Problem is it contracts more than it expands! It can be quite a headache! I remember having to weld a 6mm wall-thickness steel pipe to a 10mm steel plate which was then to be bolted to a flat surface (just like a pier). I actually tacked (small welds) the base-plate to the welding-table prior to welding in an attempt to reduce the distortion, then listened to the tacks breaking free of the table one-by-one as it cooled! I later learned that the solution was to use a thinner plate and slightly dish it using a press so that it pulled back into shape when it cooled.

Anyhow, that was a long-winded way of saying Arthur is right, the base of all welded piers will be slightly off-true.

Ron, I do like the idea of a wooden pier. Perhaps something made using ship-mast manufacturing methods would be good, with a steel-plate top and bottom... It would be expensive, but rather classy!

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RobH

RobH

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I experimented before I attached the scope Martin, and at first just listened very closely.

To check that I'd cured it completely, I stuck a small microphone onto the side of the pier and watched what happened when I tapped the pier, using a professional spectrum analysis program I have called SmaartPro, which is capable of very high resolution. This will show any noise/resonance from 16Hz to 21 KHz.

The addition of the oil killed off any vibrations completely, as I mentioned.

Cheers

Rob

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SteveL

SteveL

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Ron, I do like the idea of a wooden pier. Perhaps something made using ship-mast manufacturing methods would be good, with a steel-plate top and bottom... It would be expensive, but rather classy!

Can you find a mast from the local shipyards? Avast me hearties, prepare to be boarded ye land lubbers, etc etc

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Kai

Kai

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Avast me hearties, prepare to be boarded ye land lubbers, etc etc

Okay i think you've had enough now Steve , put those Jaffa cakes away till breakfast :)

Either that or Captain Pugwash had a really profound effect on you !!!

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FLO

FLO

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Rob, the sand/oil solution sounds like a winner :) It would also prevent the pier rusting from the inside. So I guess we can summarize by saying a large-diameter steel pipe welded to a large/thick base-plate is the most practical solution. That it should be bolted directly to the concrete and that any adjustment should be done at the top, not the bottom. Personally I suspect reinforcing webs are an unnecessary complication, unless perhaps at the base of the pier, even then I am not convinced of their effectiveness.

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barkis

barkis

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Okay i think you've had enough now Steve , put those Jaffa cakes away till breakfast :)

Either that or Captain Pugwash had a really profound effect on you !!!

Hehheh. Who was his adversary, I've forgot, but I think his ship was the Black Pig. Or was that Pugwash's vessel?;)

Jaffa Cakes alcoholic are they?:)

Ron.

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FLO

FLO

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Hang on Arthur, you might not be in the clear yet :)

How important is it that a pier be modular? Can a modular system be made as sturdy and effective as a regular pier?

And I am surprised nobody has mentioned price - these things aren't cheap!

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RobH

RobH

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And the other couple of characters, the significance of their names lost on us innocents in the '60s when the world was a simpler place? :)

No....family forum!

Steve, a thing I found was that when you fill a pier with sand and oil, make absolutely sure that the sand is completely dry, or the oil displaces the water and you get a layer of water that rusts the pier from the inside....as I found out :)

Cheers

Rob

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