Telescope Reviews: Doubts with a pier, (planning my observatory!!)

The reason I went with the 10" was because the bolt circle under the 4" pipe flange I was using as a pattern was way too close to the edges of the 8" sonotube I started with. This meant I would have less than 1" of concrete on the outsides of the bolts because the form was so close to the same size.

Realistically, I'm sure this would have been fine because we're talking concrete merely holding a telescope, I'm not trying to install a crane or tie a ship to it.

Still, I just didn't like the looks of it. So I took the 8" back and exchanged it for the 10", a couple bucks difference and big peace of mind.

I think using your single bolt approach the 8" will probably be fine since it will be centered in the pier. On the other hand, I'd consider going to 10" for the extra damping.

The price difference in tubing isn't much and it's only another sack or two of concrete. Here in the US 4'x10" Sonotube is about $9 and 80 lbs of "Sackcrete" ready mix is about $2.80 a bag. I used 11 bags for the pier for my 6" and 15 bags for the shorter but fatter pier for the 12".

I intentionally overdid the bolt circle/flange size and bolt size on the pier for the 12" because I intend to seek, find, and purchase one of the old 2" shaft "Observatory Class" Cave GEMs and I wanted to make sure I had enough underneath it. There is no way I can afford a modern mount capable of handling a 12" newt, but I think I can swing a classic old school monster.

I have done three piers now in three months. It's so easy it's a bit addictive, especially when you experience how stable they are. They're lined up in the yard and it's really great to have multiple instruments you can just walk between without tripping over tripods and stuff. The wife is getting concerned.

Number one was an experimental deal just to see how it went, I'd never used concrete for anything. I read up on it a bit and it's real simple and works as advertised. It's all in the setup. Don't add too much water, except on the top pour where you're setting the bolts, you will want it a tiny bit sloppier so it sets around your bolts closely with no voids and is easy to 'float' by tapping the form a little.

The first one was for my ETX60, and was simply a hole a few shovel blades across and 2' deep, with 6' of 4" PVC pipe put in it centered on a steel "t" post ( you see these used for field fencing). Once the hole was full I started filling the pipe. Came out fine for such a small scope. I suppose 6" pipe would have been better, but I was just messing around.

Then I got ambitious .

The footing for the 10" pier/6" scope is about 2' in diameter and 2' deep, with a 20" tall, 10" diameter pier and 4 5/8" J bolts. If you go to the Classics forum and look for my thread on the MTS-SN6, I have pics of the pier.

The footer for the 16" pier/ 12" scope is 3' diameter and 3' deep, and features a 16" pier about 10" tall with 4 x 3/4" bolts.

I couldn't get 16" sonotube off the shelf, so I went to the housekeeping area of the store and picked up a plastic wastebasket of the size I wanted, cut it to length and used that as the concrete form.

You'll find that once you do this and get past the doubts, it's just plain simple and fun to do piers, and it's fast. How cheap it is of course depends on supplies in your country. Remember to scavenge up a bit of chicken wire or some scraps of field fencing to put in the footer to keep it together over time, and a few T posts or more fencing for the column itself. there are ample pics of this on the web and here on the site. Don't over think it, it's as basic as it looks.

You're going to find once you're done that it was a snap, and the benefits you reap are so great you'll be thinking about the next one.

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"Ignorant people think it's the noise which fighting cats make that is so aggravating, but it ain't so; it's the sickening grammar they use." Mark Twain

Edited by MtnGoat (07/31/08 01:22 PM)