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Dunceath Observatory - an Explora-Dome build

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#1 Jack Morris

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Posted 30 December 2013 - 11:46 AM

Now that the winter rains seem to have set in, maybe I will find time to report the saga of my recent design/build process. First, a little background: I returned to astronomy a little more than a year ago after a very long hiatus. I started with an Orion 10" Dob which I have thoroughly enjoyed. However, I became frustrated chasing Jupiter across the sky at high magnification so last winter's project was a home built EQ platform mounted on a JMI dolly for easy moves. That setup works well if I am careful to not tip it over! During the past year I picked up a used CG5-AGT and an ES 80ED (a grab and go which I love), followed by a good used C9.25. Unfortunately, I do not have a place where I can leave the CG5 and C9.25 set up overnight, there are too many trees in my yard, so my preferred observing site is in the horse pasture behind my house. But I don't trust the horses with my mount and scope, and I have decided I am getting getting too old for a nightly set up, align and take down. So I started investigating observatories. First, I investigated and actually partially designed an ROR, but here in SE Louisiana dew is a major problem so I decided to switch to a dome design instead. I won't bore you with the selection process - I ultimately selected the Explora-Dome.

The finished product in my avatar and previously posted in the observatory pictures thread, page 51. Today's picture is "The Office".

Note: The decision to proceed was helped by the fact that I am a retired, former world traveling engineer, now living in rural SE Louisiana (home) who needs an occasional design/build project to preserve his sanity! :lol:

Next chapter - site selection and preparation

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#2 Raginar

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Posted 30 December 2013 - 12:48 PM

Looks good! More pictures!

#3 RobertED

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Posted 30 December 2013 - 04:19 PM

It's awesome!!...even got a "Captain's Chair!!!".....

#4 csa/montana

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Posted 30 December 2013 - 06:21 PM

Really nice! I used the pegboard also, and the blue looks very similiar to mine; I love it! :waytogo:

#5 Jack Morris

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Posted 30 December 2013 - 08:35 PM

csa,

I may have gotten the idea from you. Plagiarism at its best. More on the color, much later.

More to come, probably tonight.

#6 csa/montana

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Posted 30 December 2013 - 08:58 PM

Not Plagiarism at all; rather I'm flattered if you did get the idea from me! :)

You've done a really nice job finishing it off; absolutely beautiful!

#7 Jack Morris

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Posted 30 December 2013 - 09:37 PM

I had set up the dob and the grab n go at various points in my yard, but none had a good view of the whole sky. My position of choice became the top of a gentle rise in the middle of the horse pasture where I had a view of the entire sky to an altitude of less than ten degrees all around. However, this was more than 100 yards from the nearest building with electricity. Ultimately, I decided I did not really need to see anything below an altitude of twenty degrees. I used my grab n go and a digital inclinonometer to find a location closer in that satisfied that requirement. I finally chose a spot where the limiting altitude was a pecan tree to the NE whose top branches reach seventeen degrees. This spot was only about 120' from a garden shed from which I could get electricity. From there I located true north and placed a stake about 500' north of the proposed position of the pier. More on that later.

I first cut the grass in the area down to the ground with a weed eater over an extended area. With the help of my son, an experienced carpenter, we proceeded. I planned to do the pier first, but when the J-bolts didn't arrive when expected we decided to start with the foundation for the 10'X10' building instead. We first cut the outer 2X8s to size and connected them with 4" deck screws. We squared this structure by equalizing the diagonals and braced with diagonal 2X4s. We put the square in place, shimmed it level and marked the locations of all the support posts. The site has only a slight slope from SW to NE. We then moved the square frame out of the way and proceeded to dig post holes. The corner posts are treated 4X6s and the intermediates are treated 4X4s, all from my scrap pile from previous projects. The corner posts are 3' in the ground and the intermediates are 30". Note that ground frost here could be measured in millimeters, if at all, and residential foundations are typically only 12" deep.

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#8 Jack Morris

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Posted 31 December 2013 - 03:51 AM

With the holes dug, we put the frame back in place, shimmed it to desired height, and carefully leveled. The posts were then screwed to the frame so that they extended down into the holes. The holes are a little extra deep to allow the concrete to completely surround the bottom of the posts. Quikrete was applied by the "mix in place" method: 1/2 gallon water, 1/2 sack of quikrete, tamp thoroughly to mix and get the air out, and repeat until the hole is full. One of the outside 2X8s was slightly bowed to the outside, so we pulled it back in line with ratchet straps before concreting its intermediate post. It was Friday afternoon so we let it sit for the weekend. On Monday we started installing floor joists on the west (back) side complete with joist hangers and angle brackets in the corners. The J bolts arrived so I scheduled a small concrete mixer for the next day. We placed the three sheets of 3/4" treated plywood flooring on the west side joists to use as a stand for the mixer next to the pier hole.

The picture shows the rebar cage in the pier hole - next edition

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#9 Jack Morris

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Posted 31 December 2013 - 04:07 AM

Pier Design
What I have at present is a C9.25 on a CG5 mount, but I didn't want the observatory to be limited to that configuration. Therefore, the pier is designed for a CGE Pro mount. Why the CGE Pro? First, I easily found dimensions on the Celestron web site, and I didn't have much luck with most others. Second, the CGE Pro with its "electronics pier" is unusually tall for its class. So I figured if I designed for it, I probably would be able to accommodate anything else that I might get in the future. The pier height is such that, with the CGE Pro, any scope I might mount on it would be able to see over the shutter threshold to within twenty degrees of the horizon.

The pier footing is a couple of inches short of three feet deep. The base, up several inches, is three feet in diameter. From there, it tapers at about thirty degrees up to about ten inches below the surface, where it is 12-3/4" in diameter. From there, it is a uniform cylinder to the top where the 3/4" SS anchor bolts extend up another 4". There are six pieces of 1/2" rebar near the bottom of the hole arranged in a six point star pattern around the base of a central six foot high rebar cage which extends upward to within an inch of the top of the concrete. This rebar cage is wrapped in 6"X6" reenforcing wire to within one foot of the top. The entire pier is cast from 5000 psi Quikrete. The pier was formed by digging a 12" diameter hole almost three feet deep with a post hole digger, then using post hole digger and sharpshooter, the hole was tapered from ten inches below the surface at thirty degrees until it was 36" in diameter at the bottom. This was fairly easy to do in early November, if we tried it now the hole would fill with water and cave in :lol:. The hole was carefully trimmed at the top to fit a 4' piece of 12" Quiktube which is 12-1/2" ID, 12-3/4" OD. Concrete was mixed, three bags at a time, poured and tamped until it was just below where the Quiktube was to start. Pouring directly into the hole from elevated platform was easy. The Quiktube was a snug fit in the hole and adjusted to the proper height and leveled. Pouring continued, but now with a shovel from the top of the tube. Fortunately this went faster than the base. There was much tamping and tapping with a mallet to settle the concrete as the tube filled. When the concrete was up to where the bottom of the J bolts would be the template bearing the J bolts was inserted in the end of the tube.

Next edition -

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#10 Jack Morris

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Posted 31 December 2013 - 04:47 AM

A template for the location of the J bolts was made from a 1-1/2" piece of plywood from my scrap pile (sink cut out from a counter top project). The layout was a 12-1/2" diameter circle for the outside, a 6" circle for an inner cut out. Three radials very carefully marked out 120 degrees apart and a 10" circle to locate the three anchor bolts. The anchor bolt holes were drilled using a forstner bit for precision, and the inner and outer circles were cut with a sabre saw, slightly oversize in the case of the outer circle. The outside diameter was then carefully sanded on my table saw until it would just fit snugly inside the Quiktube. Two finishing nails were driven in slightly at the ends of what would be the N-S radials. These would be used for sighting on my previously mentioned true north marker. The anchor bolts were then bolted into the template with just enough thread for the top most nut and washer, and with the "foot" turned toward the center.

When the concrete was up to the bottom of the "feet" of the anchor bolts in the Quiktube, the template was inserted and carefully aligned to true north. Concrete was then added through the central hole to within 4" of the ends of the bolts. I had worried about being able to get the anchor bolts all the way in to the concrete and being able to align if the tube was filled first. The central hole solved that problem.

Note the finishing nails in the picture.

After the pier had been allowed to set up for a few days, the Quiktube was removed, and the pier was finished with an 1/8" coating of mortar applied by hand and with a masonry brush. This filled the few voids around the outside and gives the pier a nice sand finish.

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#11 gillmj24

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Posted 31 December 2013 - 09:39 AM

It's amazing how much more room gives you than just an 8 foot cylinder.

I have POD walls and bays and it is still cramped but that's all I could fit on my deck.

#12 Midnight Dan

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Posted 31 December 2013 - 10:48 AM

Hi Jack:

Nice observatory! I'm interested to see the rest of the photos!

I built mine in a horse pasture too. Put a fence around it to keep the nosey beasts away:

(Click on images if you want to see a larger version)
Posted Image

Posted Image

Since I was also about 100 yards from electricity, I went with solar power:
Posted Image

-Dan

#13 Jack Morris

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Posted 31 December 2013 - 05:47 PM

Hi Dan,

I don't have a fence, so I have to keep the door closed. This old Welch Pony (more than 30 years) would come inside if given a chance :roflmao:!

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#14 Midnight Dan

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Posted 31 December 2013 - 06:40 PM

I'm surprised they don't chew on the deck wood! Of course, in Louisiana, you have a lot longer growing season than we in the frigid north and the animals can keep better occupied with "real" food. :grin:

-Dan

#15 mikey cee

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Posted 31 December 2013 - 06:49 PM

As a former layout expert in framing it's nice to notice the correct riser height on the first tread! :roflmao:Mike

#16 Fish

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Posted 31 December 2013 - 07:11 PM

Dan,

Nice to see someone else had the same idea as I. I placed an Exploradome on a 10' X 10' building with 6' walls. With that height I can walk to the inside walls without bending down; you wouldn't believe how much more usable space that gives!

I use all cameras so the extra height of the mount above the floor is of no concern. It does add more complexity - remote mount control, remote focus, slaved dome rotation, etc.

Mine's been up 5 years now. It's a constant work-in-progress but the best thing I ever did for enjoying the hobby. I'm sure you will think so as well.

Regards, Marc

#17 csa/montana

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Posted 31 December 2013 - 08:48 PM

Hi Dan,

I don't have a fence, so I have to keep the door closed. This old Welch Pony (more than 30 years) would come inside if given a chance :roflmao:!


He's just making sure you do things correctly! :lol:

#18 Jack Morris

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Posted 01 January 2014 - 05:35 AM

Hi Carol,
SHE is very gentle, a great training pony for our grad daughters (who now have children of their own), but with typical pony stubbornness. She is impossible to run off, so we had VERY, VERY close supervision at times :foreheadslap:.

#19 Jack Morris

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Posted 01 January 2014 - 06:20 AM

The hole in the template was actually 8" diameter.

While on the subject of the pier, I will jump ahead a little and talk about the extension for the CG5. The CGE Pro is about 14.5" taller than the CG5, so I obviously had to have an extension. First, I purchased Dan Harmon's excellent CG5-AGT adapter (pierplates.com). I also got the 3/4" anchor bolts from Dan. This adapter has 4" "legs", so it is about 5" taller than Dan's CGE Pro adapter. That meant I needed another 9.5 inches (roughly). I designed a steel pier extension with 1/2" base plate 12" in diameter, with a 6" center hole (for access to the mounting screws for the CG5 adapter). The extension is 8" tubing (8.0" OD), 8-1/2" long, with a 1/2" thick by 8" diameter top plate. Of course, the top plate has holes for mounting the CG5 adapter. As an afterthought I designed an EP holder, machined from 1/8" steel plate, with 9 each 1-1/4" and 2" holes evenly spaced. This EP holder is mounted (trapped) between the extension and the CG5 adapter, and held by the same screws. The steel work was done by a local machinist who has done repair work for me in the past. It is finished with Rustoleum "hammer finish" black paint.

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#20 Jack Morris

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Posted 01 January 2014 - 07:57 AM

I prepared a complete drawing of the entire structure using CAD, including three elevations and three plans. Here is a portion of the drawing showing the floor plan, including sub structure and 3/4" plywood layout. Everything here is pressure treated, and all joints are connected with deck screws as well as galvanized steel joist hangers or angle brackets.

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#21 Jack Morris

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Posted 01 January 2014 - 08:04 AM

I won't bore you with a blow by blow of wall construction. Everything is conventional except all connections are with deck screws, the studs are 48" long and there is a single top plate. Here is the "East" elevation, actually the building faces 120 degrees.

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#22 Jack Morris

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Posted 01 January 2014 - 11:19 AM

I had downloaded and studied the instructions for building a 10X10 wood building from the Explora-Dome web site. Up to this point everything is pretty much according to the instructions, except that I somewhat simplified the floor structure to allow using three complete sheets of plywood, with minimum cutting, leaving just the center 2'X2' area around the pier. I would later buy a quarter sheet from Home Depot and use half of it to complete the floor.

With the roof/dome support structure I started to deviate. The Explora-Dome instructions call for 2X10s for the main cross members, doubled in the case of the full length ones (for snow loading), and side braces cut from 2X10s. First, we don't know what snow is down here (not quite true, but close). Second, I think 2X10s are over kill for the support of a 180# dome. The roof of my home has 2X6 rafters on 16" centers, and the spans are well over 10'. It has survived multiple hurricanes with NO damage. I did use 2X10s for the two full length cross members, but undercut them in the middle portion to essentially 2X6 dimensions. The two short (86") cross members were ripped to 5-11/16" (to match the main members) from a couple of scrap 2X8s that I had. The side braces are angled 2X6s, and I did add one extra on each side (5 instead of 4, each side). Every joint in the roof/dome support structure is reinforced by a galvanized steel angle bracket installed with three 1-1/4" screws in each member. This gives me about 3-1/2" more head room under the roof which is significant.

Here is the plan drawing with cutting details, refer to the last post for an elevation view.

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#23 Jack Morris

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Posted 01 January 2014 - 11:45 AM

High quality "R panel" painted steel, from the local Mueller outlet, was installed running from the bottom of the outside "2/3s" down to the just below the plywood flooring. Closed cell inside seal strips, also from Mueller, were installed around the bottom, and outside seal strips were installed later before installing the roof panels. This is a good, tight system if done carefully.

I followed the Explora-Dome instructions to bend the siding around the corners of the building. I WOULD NOT DO IT AGAIN!!! It would be much easier, and neater, to cut the siding at the corner and purchase (from Mueller) and install matching 2"X2" angle over the corners.

We were very remiss in not documenting the wood building process, but here is a picture of the complete structure waiting for arrival of the dome and roof panels (and rain, which came in spades).

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#24 Starman27

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Posted 01 January 2014 - 12:00 PM

Jack,
Looks like a great build. Thanks for sharing the plans and images.

#25 MHamburg

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Posted 01 January 2014 - 12:12 PM

Jack,
Good luck and keep us updated with more pics.
Michael






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