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Pier Leveling -- myth or must?

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#1 ReMax

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Posted 16 May 2013 - 11:33 PM

I'm in the process of fabricating a steel pier that will eventually host a G11 mount (with Gemini II) controlling an AT8RC. While researching the design I ran into conflicting opinions with respect to the leveling plate (atop the pier). One school of thought says the pier must provide an absolutely level base for the mount (hence the leveling plate), and the other says that a level base is not only unnecessary for telescope alignment, but merely adds another opportunity to introduce flex and vibration. However, the vast majority of commercial piers have leveling plates -- am I missing something here?

#2 Patrick

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Posted 16 May 2013 - 11:38 PM

Technically you don't need to have a GEM mount level, but I've found that it really helps especially when polar aligning. As far as flex goes, use big bolts. I have 1/2" bolts on my pier plates with no issues I can detect.

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#3 EddWen

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Posted 16 May 2013 - 11:51 PM

While it is correct that the plate need not be level to get a good polar alignment, it does make the alignment easier. There is less interaction between the changes made to the two axis.

With proper design there should not be a greater tendency to flex or vibrate.

#4 ReMax

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Posted 17 May 2013 - 12:08 AM

Thanks for the input. Fortunately, that's pretty much where my head was at. I have 1/2 bolts cut in, but wanted some "expert" advice before committing the welds. One nice part is that having leveling plate makes it far easier to bolt on a mount adapter...

#5 tomcody

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Posted 17 May 2013 - 08:26 AM

One thing to consider is ground settling, and the pier base tilting ( happened to me in central florida from hurricane rains, even with a four foot deep concrete base under the pier). if you have threaded rods connecting the base to the pier, you can easily re-level the pier at any time, just set it up like a street light pole base on the side of the road, they support the entire pole on threaded rods and it sits on nuts instead of the concrete.
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#6 korborh

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Posted 17 May 2013 - 09:14 PM

If it is a permanent setup then one time effort of polar aligning a less leveled base is not an issue.

#7 blueman

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Posted 17 May 2013 - 10:18 PM

Let's just say that level is never bad. But not level is no a serious problem. However, if you are putting together a pier, you should try to get it level in the begining.
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#8 ReMax

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Posted 17 May 2013 - 10:26 PM

Although I'm attaching the pier to a concrete base with threaded 1/2" rods, I'm a little nervous that lofting the base plate on nuts could create an opportunity for vertical resonance (i.e. bounce) across the pier base plate. I know that such vibrations are probably negligible, but I figure as long as I'm building a permanent mount, I might as well try to remove all sources of noise that I can think of.

#9 blueman

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Posted 18 May 2013 - 12:14 AM

I would not worry too much about that, I have seen plenty done that way and it seemed to work fine.
But you can always put washers under the nuts to the pier, so that you have more contact to the pier.
Blueman

Although I'm attaching the pier to a concrete base with threaded 1/2" rods, I'm a little nervous that lofting the base plate on nuts could create an opportunity for vertical resonance (i.e. bounce) across the pier base plate. I know that such vibrations are probably negligible, but I figure as long as I'm building a permanent mount, I might as well try to remove all sources of noise that I can think of.



#10 M13 Observer

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Posted 18 May 2013 - 12:02 PM

Although I'm attaching the pier to a concrete base with threaded 1/2" rods, I'm a little nervous that lofting the base plate on nuts could create an opportunity for vertical resonance (i.e. bounce) across the pier base plate. I know that such vibrations are probably negligible, but I figure as long as I'm building a permanent mount, I might as well try to remove all sources of noise that I can think of.


If the base plate you are speaking of is the one that attaches to the "studs" set in the concrete then get it all as level as possible at pour time and get the pier post as square as possible to the top and bottom plates. Then, when installing the pier post, in between the base plate and concrete, install a 3/4 to 1.5" (double up) outdoor rated plywood spacer with holes drilled to mach the "studs". Tighten down the base plate with nuts and lock washers and continue to tighten to adjust the level of the mounting plate on top of the pier post. The plywood acts as an excellent vibration dampener and by tightening the nuts as needed can be used to further adjust the level of the top plate if things shift slightly.

#11 ReMax

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Posted 18 May 2013 - 05:43 PM

The plywood damper is a clever idea. I'll try it. Thanks.

#12 Patrik Iver

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Posted 19 May 2013 - 01:26 PM

When I built my pier 9 years ago, I dug a pretty deep pit and filled it with close to 400 kg of concrete. Regardless, it shifted a bit one winter, which made me really glad I had the possibility level it using the levelling bolts.

For the load you will use your with, I don't think decently sized levelling bolts would be a source of instability. Mine are 12 mm (~1/2"), spaced in a ca 250 mm square (~10"), and kept as short as possible, i.e. the pier base as close to the concrete as possible.

#13 korborh

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Posted 19 May 2013 - 02:32 PM

Leveling it as best as you can when making the pier/foundation is a good idea. However it is not worth compromising the stability of the structure. Even if it shifts later, the mount can be aligned using Alt/AZ adjustments.

Just keep a flat base for the mount - no need to spend too much energy on leveling and create unstable structures with riser botls etc. for a permanent EQ mounts setup.

#14 gnowellsct

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Posted 19 May 2013 - 08:20 PM

Leveling not strictly necessary on a permanent set up.

If you are portable--I use an ATS pier which is portable, then leveling matters. It matters because it helps your subsequent polar alignment, because the altitude setting of the mount on tripod will be very close to the previous set up, minimizing the altitude adjustment.

On a G11 that doesn't really matter. The altitude adjustment is so ergonomically comfortable that it is at least as easy as leveling your pier.

With an AP mount 900/1200 it matters. It matters because the positioning of the altitude adjustment is very hard on the wrist. I didn't check out the AP 1100 and 1600 to see how wrist-friendly the altitude adjustment is.

For a permanent pier I would level as best I could just because it is a sign of good workmanship. But you don't have to worry if you're a quarter or a half a degree off. It might affect, at the martin, where your meridian flip is in relation to the real meridian.

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#15 blueman

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Posted 19 May 2013 - 09:45 PM

Really? My AP 900 is quite easy to adjust either DEC or RA. I could adjust it with one finger if I needed to do so.
Blueman

Leveling not strictly necessary on a permanent set up.

If you are portable--I use an ATS pier which is portable, then leveling matters. It matters because it helps your subsequent polar alignment, because the altitude setting of the mount on tripod will be very close to the previous set up, minimizing the altitude adjustment.

On a G11 that doesn't really matter. The altitude adjustment is so ergonomically comfortable that it is at least as easy as leveling your pier.

With an AP mount 900/1200 it matters. It matters because the positioning of the altitude adjustment is very hard on the wrist. I didn't check out the AP 1100 and 1600 to see how wrist-friendly the altitude adjustment is.

For a permanent pier I would level as best I could just because it is a sign of good workmanship. But you don't have to worry if you're a quarter or a half a degree off. It might affect, at the martin, where your meridian flip is in relation to the real meridian.

Greg N



#16 SkipW

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Posted 19 May 2013 - 10:37 PM

I don't think that's what gnowellsct was referring to. He said the elevation adjustment of the polar axis - adjustment for latitude - was non-ergonomic.

[edit] spelling.

#17 blueman

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Posted 19 May 2013 - 11:40 PM

I am saying that is not true, it is very easy to turn. It sets quickly and that is about all one can ask for isn't it?
Blueman

I don't think that's what gnowellsct was referring to. He said the elevation adjustment of the polar axis - adjustment for latitude - was non-ergonomic.

[edit] spelling.



#18 wasyoungonce

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Posted 19 May 2013 - 11:54 PM

I'm getting a pier made for me (for G11), all done except powder coating. Should have it soon.

As for levelling plate...not needed. Just an extra source of flexure & vibration IMHO.

#19 SkipW

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Posted 20 May 2013 - 07:01 PM

I am saying that is not true, it is very easy to turn. It sets quickly and that is about all one can ask for isn't it?
Blueman

Sure is.

Since gnowellsct was commenting on hard elevation adjustment and you replied with a comment about adjusting in RA and Dec with one finger, it sounded like you were addressing a different topic.

I don't have one of these mounts so I can't tell who's right, but I do wonder why your experiences are so different. Perhaps you both are and have different versions of the mount.






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