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Observatory Build Underway


malc-c

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Just got to think what to do with the 2-3 cubic yards of earth that has now formed a mountain in the middle of the lawn ! - I know.. my 17yrs old son has just asked me for a sub until his allowance comes in... There are 50 rubble sacks in the shed... I've got just the job for him :D:p

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You know when you're too deep in astronomy when you see a picture like this and think 'I could remove that digger arm and mount a big dobsonian on that!"

I've been looking for the USB port on it so I can plug it into Stellarium to control it :D:p

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Well, a few hours later the footings are dug, along with a hole for the mount base.

diggerE.jpg

Been pricing up ballast and cement and hope to order this for delivery by next weekend. I have also managed to strike a deal with my son to get the huge pile of earth bagged up ready for dumping at the local council tip. He wants his moped fixed so I've agreed to foot the bill if he helps by clearing the spoil and laboring for me when it comes to pouring the footings for the walls. - Works out about the same cost of hiring a skip but then I would still have to get a couple of cubic yards of earth some 40 yards from the back garden to the road (nearest access point) to dump it in the skip, so that seem a result.

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That makes quick and easy work of it :p Took me a week to dig a hole for the pier :D

Nice to see progress though :( Well done :o

Edited by Gina
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Footings!! You could almost build a house on them! You will have one sturdy obsy!

That's the idea :D

The idea is that the footings will provide a level base to build a dwarf wall that will be one or two courses above ground at the lowest point. Then with the shuttering for the mount base in place, and a few of those re-enforcing panels in place, the slab will be poured - thus ending up with a perfectly level brick skirted base, 16' x 8' on which to bolt the flooring framework. - well that's what the guy next door suggested and he does ground works for a living for the past 30 years !

I'm still undesided on the mount... part of me wants to go the same route as Gina, with a concrete pier, the other suggest a traditional tube with flanges that is bolted to the foundation. The latter would allow me to work out the height of the pier once I have the walls in place so I can get a better idea of clearances...

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Yes, I'm doing it the other way round - decided how high I want the mount, building the pier to suit then building the walls to match that. Steel piers are too expensive. The scope height and position are paramount IMO.

Edited by Gina
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Well it's been a busy week. The first thing I dd was get my levels set for the footings, thanks to Steve's laser leveler it was a breeze to insert lengths of old pipe as markers. Then it was a call to Jewson's to order 2 bulk sacks of ballast and 16 bags of cement. Then a call to HSS and booked a mixer for the weekend... It's amazing how quick you can spend £200 !!

The ballast and cement arrived on Friday morning, and thanks to my son and his friends moved the cement to the safety of the shed just in case it rained, and then they shoveled the ballast out of the bags and barrowed it to the rear garden.

8.00 am this morning I made a start

footings2.jpg

Fortunately the weather held off with only just the odd spot, and I mean spot of rain whilst we continued with the mixing and laying of the concrete. My Son and his friend turned up and helped with the loading of the mixer, which helped no end.

By 2pm it was obvious that we were going to be short on ballast. A quick trip to Wickes and we returned home with 10 bags which was just enough to finish off the final leveling of the back trench.

So approx 7hrs after starting, we had mixed 2 tonne of ballast with 14 bags of cement, and I still need to do the pier base ! But that will have to wait until next week as we have other plans for tomorrow.

footings1.jpg

Next step, mark out and make the shutters for the pier base, then order another bulk bag of ballast, 10 bags of cement, bulk bag of sharp sand and around 300 bricks. Hopefully by the time the bank holiday is here in two week time I'll be able to start building the suspended floor.

Edited by malc-c
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Looking good and pretty much how I would do it as well. As for the pier my personal preference would be for a steel pier over concrete. That way if you move house you can take it with you. Plus it gives me something else to design for my hypothetical obsy.

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This is the construction for the floor / walls

Basically a suspended floor using decking joists, supporting 18mm ply flooring. When drilled and screwed should provide a strong structure. I'm not yet certain if I will but the flooring upto the studwork, or take the floor to the edge of the brick and place the studwork on top.. .

post-23388-13387760489_thumb.jpg

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I would personally build the studwork off your brick walls rather than off the floor.

I would feel more comfortable knowing that my sole plate was fixed to the brick directly.

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looks nice and solid...but if that blue line is a DPC it's a little close to the ground. Typically you would take 2 courses above the ground using engineering or other frost resistance spec before a DPC.

Also a treated batten to act as a sole plate (on topof the bricks) would be better to hang the joists off...this distributes the load a little better and is easier to fix into...as you're building a timber frame on top this will also give a better footing to the frame to fix your noggins and studs to. If each of these goes into brick you'll have a bit of a nightmare.... hitting holes (or frogs if you've gone old school with the spec.)

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looks nice and solid...but if that blue line is a DPC it's a little close to the ground. Typically you would take 2 courses above the ground using engineering or other frost resistance spec before a DPC.

Note taken ;) - thanks

Also a treated batten to act as a sole plate (on topof the bricks) would be better to hang the joists off...this distributes the load a little better and is easier to fix into...as you're building a timber frame on top this will also give a better footing to the frame to fix your noggins and studs to. If each of these goes into brick you'll have a bit of a nightmare.... hitting holes (or frogs if you've gone old school with the spec.)

The sketch isn't that clear. Basically the studwork hopefully will do that job - something like the attached, or are you suggesting I still need a soleplate ?

post-23388-133877604895_thumb.jpg

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Looking at that sketch I might be tempted to put the joist hanger on top of the sole plate.

Normally a wall plate will be used to bear any kind of joists either by a joist hanger or directly. The wall plate (or sole plate in this case) will be bolted down to your block work allowing the the load to be distributed more evenly.

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Normally a wall plate will be used to bear any kind of joists either by a joist hanger or directly. The wall plate (or sole plate in this case) will be bolted down to your block work allowing the the load to be distributed more evenly.

Something like the attached ?

post-23388-133877604908_thumb.jpg

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Ok, how does the attached look?

Option 1 is the traditional wall plate utilising a joist hanger.

Option 2 is where there is no joist hanger and the joists are sat ontop of the wall plates

Option 3 is where a wall plate is bolted onto the face of block or brickwork and then a joist hanger is used.

There are also other options but these are the most common. Personally I would use either option 1 or 2. Option 2 is good as long as the resultant floor levels are not put too high i.e. requiring steps to get into the obsy and or increasing the overall height.

Hope that help?

Joist Hanger Options.pdf

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OK I've been over and over the design again and again. The observatory will run approx East / West so the side walls will be to the North and South. I'm trying to work out the maximum height the walls can so that I get a decent viewing of the East / South / SW horizons. The option I am favoring is to raise the floor so that the angle from the mount to the top of the wall is very small, but this then has the disadvantages of very low headroom in the observatory, and for visual, means that there will be little protection against the wind. If I opt for a full height (say 1.8m) wall, then the scope would need to be on a high pilar and steps would be needed to see anything directly above.

The attached is based on measurements taken from the 200P on the tripod with the legs set to minimum - 1.3m is the minimum height with the scope parked with the OTA horizontal

Any ideas or suggestions ?

post-23388-133877605504_thumb.jpg

Edited by malc-c
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Exactly the dilemma I've got!

I think I'm beginning to home in on a design for my shed. But the wall height and scope height are still straining my brain!

I'd like my pier lower but for headroom I don't want the walls too low but low enough to be able to aim the scope close to the horizon.

The design I like best is "Harry's Astro Shed" http://www.harrysastroshed.com/shed.html

I'm thinking of basing my design on that.

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The only thing to watch in that sort of design is water ingress at the join of the two halves.

I Don't think that there is any real win-win option, you gain on the swings but lose on the roundabouts ! - good headroom / poor horizons.

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