Jump to content


Photo

How deep for pier with cgem dx

  • Please log in to reply
6 replies to this topic

#1 kepler22

kepler22

    Sputnik

  • -----
  • Posts: 28
  • Joined: 31 Dec 2012

Posted 09 February 2013 - 11:03 AM

is two and a half feet deep enough for my pier its
not a big mount only a cgem dx and a six inch apo.

#2 MRNUTTY

MRNUTTY

    Surveyor 1

  • *****
  • Posts: 1859
  • Joined: 22 Nov 2011
  • Loc: Mendon, MA

Posted 09 February 2013 - 12:40 PM

I planted the base of my pier below the frost line of four feet. The dimensions were 3x3x3 with a 12" diameter concrete pier extending to about 2 feet above grade. My Omega II pier is mounted on that followed by my CGEM DX head. I haven't put it all together, but that's the extent of my plans for a DX.

#3 Scott in NC

Scott in NC

    80mm Refractor Fanatic

  • *****
  • Administrators
  • Posts: 15067
  • Joined: 05 Mar 2005
  • Loc: NC

Posted 09 February 2013 - 01:07 PM

is two and a half feet deep enough for my pier its
not a big mount only a cgem dx and a six inch apo.


The bottom of the pier should probably be below the frost line. Where do you live?

#4 roscoe

roscoe

    curmudgeon

  • *****
  • Posts: 3287
  • Joined: 04 Feb 2009
  • Loc: NW Mass, inches from VT

Posted 09 February 2013 - 01:19 PM

Kepler,
Much is determined by where you live, due to frost penetration (bottom should be at least 6" below max frost penetration), and some is determined by your subsoil (hard, rocky clay is way more stable than soft gravel) but in a low-frost area, a nole 3' deep and about 2' diameter, flat on the bottom, with the pier base poured right into the hole, and sonotube or chimney liner tiles above ground (or metal pipe bolted onto the base) will do you well.
Russ

#5 microstar

microstar

    Apollo

  • -----
  • Posts: 1219
  • Joined: 05 Jan 2008
  • Loc: Canada

Posted 09 February 2013 - 01:24 PM

I had to go down 6 ft to get below the frost line, then poured a 3' x 2' x 1.5' footing connected to a 6' x 12" dia sonotube, all reinforced with rebar. If you are into imaging you can't have too much pier.
...Keith

#6 rimcrazy

rimcrazy

    Mariner 2

  • -----
  • Posts: 280
  • Joined: 03 Mar 2012
  • Loc: Overgaard, AZ

Posted 09 February 2013 - 01:40 PM

Started with a 3'x3'x3' foundation and put a 2'x2' Sonotube to the surface of the floor. Original design was to be a ROR with a 4' pier. Changed the design to a dome so now the height of the mount from the ground is just under 10'. Had the foundation modified so now it is a 5'x5'x3' foundation. This doubled the weight from around 6000 lbs to over 12,000 lbs and more than doubled the surface area (9sq ft to 25 sq ft) More important it gave a 4' diameter smooth surface to put a custom steel pier that will be 9.5' tall. Current telescope is simply a 10" Meade LX200 but eventual plan is for a 20" PlaneWave. That setup will put around 450# 10' up in the air. Only way to be stable with that much weight is a large, heavy base. This is a remote controlled imaging observatory, not visual. That makes a big difference too. I'm just not a freeze my rear end off kind of observer. The bones are too old and my eyes are too lousy for that.

Most important as said above is get below your freeze line. Second, seriously, error on the too big side. I had to redo mine. Not too costly but it would have been much cheaper had I done it all up front. In the total scheme of things, concrete is cheap.

#7 Raginar

Raginar

    Fly Me to the Moon

  • *****
  • Posts: 6138
  • Joined: 19 Oct 2010
  • Loc: Rapid CIty, SD

Posted 10 February 2013 - 01:40 PM

My 6x6 pier had a CGEM on it... I went down 30" and it is solid. Not rock solid, but it works (wood, what do you want).






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics