AstroGab

Astrophotographers hangout. Invite friends and notice chat bar on bottom.

I need advice on what i should do to make a pier. how deep should i make a 24 x 24 x ??? hole for a 12" tube? I want to make it with concrete.also Can anyone lend some pointers? I will be using a cpc 1100 on a wedge with the orion short tube piggy backed for a guide scope.will i need a plate made? Please help if any of you have done this let me know. Thanks!!

Views: 1604

Reply to This

Replies to This Discussion

At least four feet I'd say, but make sure you don't just drill a hole. It's surprising how small vibrations from someone like walking near it can influence the tracking of a long focal length on a pier. Make sure it's in soil and not touching solid surfaces, and make sure it's not just a pole but have some sort of anchor to it, so it's much more stable. You doing it striaght into a flat backyard or is there other factors?

in the ground then build a deck around it but not touching the concrete.

I'm about to rebuild mine actually, taking the deck out and redigging a more stable setup, digging deeper and squaring the corners, making it 24 inch diameter as well.

I installed my C-11 on a pier last year. Dug well below the frost line, I'm at 48" deep and made the bottom of the hole much larger than the top. If I could have gotton a cement truck where I have it I would have but borrowed an electric mixer instead. A have just about 1500 lbs of concrete in that hole.
Made a form out of plywood for my anchor bolts (4) -7/8" dia at 18" of embedment. The layout of those bolts matched the pier I had built by a local welder - 12" dia pipe by 54" tall. 3/4" thick plates top and bottom with a secondary top plate for final leveling adjustments.
I then built an elevated platform all the way around it to step up to the viewing height.
I read an aritcle about using larger diameter pipe verses smaller and what it said made sense to me. So far - she's rock solid and been through two winters and hasn't budged a fraction of an inch.

Russ

Thanks Russ!!

Glad this came up, I'm starting my hole tomorrow. I've got the 8" plate system ordered from this guy
http://www.pierplates.com/
I'm still in between going w/a 10" or a 12" concrete pier. I'm mounting a CGEM on it and the scopes are med. in weight (111 refrac, C8) any thoughts out there? I'm in same boat as Russ, frost dictates 4' depth and I'm not going to scrimp on the footing and plenty of rebar. Then a roll away shed. Getting psyched for the spring project! Marc

Basti I didn't know you were getting a pier, that's unreal!

Tonight is the perfect example why I want a permanent setup, I took out all my gear and the H pressure that was suppose to give me a clear sky moved off shore. So I took everything back in, now that was fun lol. This is a great thread, lots of useful info being posted. Thanks, Marc

When I did my pier, my case is 42"x 42"x 48" deep. As I filled it I placed rebar, rocks and broken block of basement block. I used 16"x16"x8" chimney block as my pier, the first block is 1/2 way cemented into the base to give it a firm connection. One thing I would not do is have your pier plate up in the air on the 3 or 4 bolts. The reason is then all your weight is placed on those 3-4 points which have a small footprint compared to the concrete pier. I was talking with Anthony from ADM and he told me that the bolts then become your weakest points. I put my pier plate right on the chimney block that way I have the support of the whole pier. Just some food for thought.

Bob

Bob - that's a good point but's it's also why you put non shrinking grout under the bottom plate.

When you think about it - almost every steel building is built on an anchor bolt system. Every ground level column is on those anchor bolts - leveled and then grouted.

Unless you're going 25 feet in the air and hanging several tons off of it the "weakest point" will be more than enough support.

The important thing is to make sure your bottom plate (base plate) is thick enough to avoid flexure. The thicker that plate the less "wiggle" you'll have.

The problem I see with tossing "junk" in the footing is it weakens it structurally. After all that hard work of digging and building a footing it would suck to have that thing break apart over time.

All this is just my honest opinion and based off of 20 years in the contruction industry as well as currently working for Schuff Steel and is by no means ment to offend anyone.

I feel that 4 foot deep is a little overkill. or am i wrong on this? would a 24" x 24" x 24" deep be a good enough base and strong enough to hold it?

For a small refractor or SCT - that might be fine. It depends on your ground type. If the ground is generally soft and moist then you'll want to go deeper or wider. You'd be surprised how much your scope at the top of the pier will move if your footing tilts 1/8".

If your ground is rocky and firm AND your frost line is shallow - you should be fine with a smaller footing. Just keep in mind that if your footing is too small it could transmit every vibration right up the pipe. Even footsteps.

If you want to image - you want stability. How much frustration would you save by spending another $100 or $200 on concrete?

RSS

© 2019   Created by Charles Dunlop.   Powered by

Badges  |  Report an Issue  |  Terms of Service