Posts Made By: Jeff Young

Well, I did manage to get same-day service on the rocks. They arrived just after lunch.

Despite assurances that 1.2 meters was 3 tons, I've got serious doubts that all that mass fits in that there hole.... :S

I hired a nice little petrol wacker to compact the hardcore.

(I used to think "wacker" was slang for "compactor" or something, but dang if it didn't say "Wacker" right on the front of it. )

Thought I'd make a second request. :S

Anyone have a digital camera and 2 minutes to spare? (Oh, and a Pan 41 to take the picture of, I suppose )

Thanks,
-- Jeff.

Here in Ireland, we call the plywood forms used for pouring concrete "shuttering". I always thought shutters went on either side of a window, but live and learn.

I used stakes to hold the shuttering -- while it worked out OK in the end, they were a real pain to get in where I wanted them and to get them tight. Looking back, I think some 15" pieces of 1/2" rebar would have done much better (the stakes tend to go off course as you're hammering them in). I was also staking into the topsoil just outside the circle I had dug, so the soil wanted to push into the hardcore filling the hole. Longer rebar could have gone straight down through the hardcore and into the dirt below it.

Lesson #2: don't cut your steel with an angle grinder over the plastic. The sparks burn little holes right through. I had to re-sheet part of it.

(If you look really closely, you can also see where the crows pecked out the top 1/2" of styrofoam isolation. :S )

Anyway, here it is, ready to go:

A mate and I spent about 4 hours mixing concrete, and another couple of hours leveling and then polishing the surface. Considering neither of us had ever done this before, it all went quite smoothly, and the results appear quite good.

This first shot shows a bit of fairly dry concrete under the steel to keep it up off the plastic.

While a few dimensions have changed slightly, the original plan sketch still gives a reasonable idea of the goal:

First there were rebar rings, now plywood....

Here's a picture of 34 plywood arcs rough-cut with a jigsaw. Standing against them is a hand-planed template which will be used with a trim-cutter in a router to finish-cut all the rest.

Then they all get glued and screwed together to form double-layer top and bottom plates for the observatory walls.

I finally got a few quotes on the steel pier. There's a lot of variability in the costs due to different shops having off-cuts on hand or having to order in 6m lengths of pipe, but that can't explain all the difference. (I'll have to write the rest down to rip-off Ireland.) Anyway, the quotes (with deltas from specification noted):

* €2200 stainless steel (4mm instead of 9 - 15mm wall thickness)

* €1090 galvanized

* €585 galvanized (8.5" instead of 10" pipe)

* €395 galvanized (16mm instead of 20mm base plate)

So much for stainless not being too much more

This thread's getting a wee bit long, so I'll continue with the observatory framing here:
http://www.astromart.com/forums/viewpost.asp?forum_post_id=365122

-- Jeff

Progress has stalled a bit. Last week I got to the point where some of my sketchy plans needed all the details worked out, but they weren't coming easy.

The first was how to fit a flat door into a cylinder. I had thought that the radius would be sufficient that it really wouldn't matter, but the center of a 32" door turns out to be some 4" in from the edge of the pad. Not much of a weathering detail (although I could put a rounded drip board on the bottom). Since my house was built by the same man (and architect) as Armagh Observatory, I went there for inspiration. And lo and behold, if there isn't a building added in the 1880's for the Grubb 10" refractor (lower right in picture) that looks remarkably similar to what I'm building. But it gets better: it also has a very nice detail of a rounded-roof vestibule for the door!

I've pretty much worked out how to fit that into my plans (although in my case the vestibule will only be a few inches deep -- just enough to give profile to the curved roof and a flat surface on the cylinder for the door).

Next up was how to suspend a floor composed of parallel joists inside a cylindrical studded wall. This required building a bit of a platform in my old kitchen (the floor wasn't level enough to just use it), and then doing a bunch of test-fits to see what was going to work. After several days (!) of moving things around and scratching my head, I think I've also figured that part out.

So hopefully, things will start to progress again...
8)