Astrokev's ROR - The Build

[Astrokev]

After a few false starts, the Build has finally started!

I posted a few designs and questions in a topic last year -  Astrokev's Observatory Build - Take 2

In summary, my observatory will be a roll-off roof design, with a small warm-room, very similar to YesYes's build of a few years ago, and also inspired by Gina and Malc-c, amongst others. I've constructed a 3D design in SketchUp (isn't SketchUp wonderful?).

Progress so far -

Ground cleared. The wooden frame in the image measures 3500 x 2300 mm. I made this to help me visualise the size of the obsy, and to help me find the best place to site it. The garden fence runs N-S, with the existing shed due North. The view West will therefore be pretty hopeless, but the view N, S, and E is not too bad. Once I'd chosen the site, I levelled the frame and used this as a guide to mark out the edges with pegs and nylon line. This proved a pain to both line it up along the top edges of the frame whilst also keeping it taught! Once done, I dropped the frame to the ground and slid it out, leaving the orange line marking the periphery.

Next job is to dig footings in the corners and in the middle of the long walls and make concrete blocks to support the base, using shuttering. Not sure how deep to make these yet - I'm thinking around 150 mm deep and maybe 4-500 wide/long.

I've marked out the position and size of the hole for the pier as I drafted it in SketchUp (~500 mm cube). As shown, the pier will be a concrete filled air-con tube (280 mm diameter. The tube needs cutting down before I sink it in the concrete). Now that I've actually marked it out on the ground, I'm not sure the concrete block is big enough. What do folks think?  The air-con tube is quite hefty and I'm worried that this will act as a good lever which might move the concrete block in the ground. Should I make the block bigger?

In case you're wondering, the ladders etc are an effort to keep my dog out of the site until I can get the base finished. Having spent ages trying to get the orange line in the right place, I don't want the dog tripping over it in the dark and ruining my hard work!

I hope you'll follow this topic, as I feel sure I'll be needing lots of help and inspiration along the way...!

Thanks for looking - Kevin

 

 

[michael8554]

Hi Kevin,

To simplify things, attach a length of angle iron to each corner of the frame  and drop this into rubble filled holes in the ground. Level the frame, raise if necessary,  and drop postcrete into the holes.

The size of the pier cube below ground is a source of endless discussion. Your pier diameter is substantial but I'd guess your 500mm cube is, as you suspect, not optimal. Some googling is recommended.

Michael

[Dr_Ju_ju]

Hi Kevin,

I also used air-con ducting, the 280mm diameter you are using, together with some 150mm duct, placed centrally inside the larger & all filled with concrete.

Using a ground auger, I sank both tubes into the into the ground, leaving approx 700mm above ground, onto which I've then mounted control power supply, PC's etc...

 

[Astrokev]

Hi Julian

Thanks for your reply. Can I ask how far you sank the tube into the ground, and did you embed it in a concrete block and, if so, how big this was?  I'd love to see a picture if you have one?

Why did you put a 150mm tube inside the 280mm one?  I'm thinking of putting a length of drainpipe down the centre of my duct tube, to run cables, rather than have them trailing everywhere.

There is a concrete path crossing the point where I need to put the pier block. If I put the main base footings in first, I'm worried that breaking up the path (which is only 4-5 inches thick) may cause ground vibration, so I've decided to break up the path before I do the main obsy footings - see image. I've decided to make the hole bigger than the 500mm square I'd originally planned (the wooden batons mark the position of the original 500mm). Still not sure how big to make it, although I'm thinking depth of the concrete block is probably more important than width, as this will help prevent movement of the pier due to torque.

Kev

 

Edited July 4, 2017 by Astrokev

[Dr_Ju_ju]

Hi Kevin,

I'll post some pics later when I get home (there are some in another thread, but I can't find them at the mo), but the hole was 1.5 meters into the ground (2 meter duct).

I drilled some holes into the side and pushed some re-bar through to anchor it in place while I filled in, and around, the duct..

The reason for the additional duct was to ensure that there was no possibility of the OTA\weights etc. hitting the pier....

 

Edited July 4, 2017 by Dr_Ju_ju
Added Pictures, as promised

[Adam J]

I dug a hole about 75cm x 75cm x 60cm (I hit the local water table at only 60cm below surface level). I can grantee you that the pier is not going to go anywhere with that sized hole.  The pier itself i was made using a square form consisting of four pieces of ply wood screwed together and is 1m x 25cm x 25cm with 3 x reinforcement bars running through it and into the base. Its as solid as a rock and possibly overkill. 

[michaelmorris]

2 hours ago, Adam J said:

Its as solid as a rock and possibly overkill. 

No such thing as overkill when it comes to telescope piers. 

[Astrokev]

4 hours ago, michaelmorris said:

No such thing as overkill when it comes to telescope piers. 

You're right there! My worry is that you do what you think will be good enough (WxDxH) but, if the pier then moves after you've finished, it's nigh on impossible to rectify !

Thanks Julian for the picture and further explanation. Your pier looks fantastic. It's interesting you comment about the risk of the OTA hitting the 280mm pier - I've been similarly anxious about this. I managed to pick up both 280mm and 150mm lengths of ducting from my last employer for free and they've been sitting in the corner of the shed for the last 6 years waiting for me to start this build project!

I've done lots of drawings and SketchUp mock-ups to try and convince myself the OTA will not foul the pier. I think it will be OK, but as stated above, it would be really difficult to correct if I'm proven wrong. Based on your own design, I may revisit using the 150mm tube aswell as the 280. And there was me thinking I'd finalised the design!

Thanks to all for your thoughts and comments.

Kev

[Astrokev]

Today I started to make the shuttering for the foundation blocks. Size is 550 x 550mm. I plan to make the blocks ~ 200mm deep, with the top edge around 120mm above ground level (the ground is a bit uneven, so the height will vary a bit), so I've had to dig a few centimetres into the ground. I hope this will help provide a firm foothold and prevent lateral movement if they are accidentally knocked.

Weather rather hot, so the parasol provided a little protection from the sun!

 

Edited July 6, 2017 by Astrokev

[Jannis]

On 4.7.2017 at 15:42, Dr_Ju_ju said:

The reason for the additional duct was to ensure that there was no possibility of the OTA\weights etc. hitting the pier....

I just learned this the hard way with my setup. I can't do much about it now though, i just hope it will be fine for the most part, and i'll have to keep an eye on the scope  when slewing or tracking for a long time.

I like your work so far!

[Astrokev]

Shuttering for the 4 corner foundation blocks are finished. Today I start to mix some concrete!

I need to give some more thought to my pier. I'm once again nervous that my 280mm air con tube will be too wide at the top and may foul my scope as it turns past the zenith. I think I've got a few weeks before I'll be ready to install the pier tube, so a bit of time to think this through with a bit of modelling!

 

[Bizibilder]

Looks like this is going to be a good build!

May I suggest that, if those four corner blocks are your "master" blocks, that you take some considerable time to get them dead level in every direction as well as dead level with each other.  Also that you firmly secure them to the ground with something like 3x2 timber driven in about a foot or so - you will be surprised just how heavy a block of wet concrete is and how much of a "mind of its own" it has!

Time spent at this stage is time well spent as it will make the rest of your build far simpler and save considerable time in the long run, knowing the base is set precisely.

[Astrokev]

Thanks Bizibilder - I hope so!

Thanks for your advice about securing the forms for the blocks. Definitely a good idea. After taking the last picture above, I did actually do this, as best as I could. The 2 forms on the grass were secured as you suggested (you can just see the timber posts on the upper left form). Here is a close up of the lower left form which shows the securing posts more clearly. These were screwed to the form after hammering them into the ground.

The 2 forms nearest the fence are sitting on a heavy-duty concrete path, so hammering posts into the ground wasn't possible. For these, I've used bricks to support each side, as shown in the second picture. Hopefully this will be secure enough.

I tried my best to get each form level, and level with each other. This proved more difficult than I expected. The orange line I'd used had sagged slightly over the last week, so I couldn't rely on this, so had to resort to using the only straight piece of long timber I could find (most of the timber used to make my base template had warped quite badly in the 90 degree heat last week!). It was all a bit Heath-Robinson, but hopefully the blocks will be aligned with each other and level enough - I guess I'll have to wait till the concrete is set to find out!

Kev

 

Edited July 15, 2017 by Astrokev

[Astrokev]

Didn't make as much progress as I hoped today, only managing to complete the concrete for one of the blocks nearest the fence (nearest the shed). With hindsight, this is probably a good thing - I think I'd prefer to see how this one turns out, regarding the concrete mix I've used (1 cement : 3 ballast), and the quality of the top surface after it's gone off, before I commit to doing the others. I actually think I made one of the mixes slightly too wet, so will try a slightly drier mix next time. I'm going to try and do a second block tomorrow.

I pushed a length of metal strapping into the wet mix to attach to the joists that will rest on the blocks. I'm only planning on using 1 strap on each block, I think that should be OK, since all the joists will be secured to each other.

Here's a few pics of the progress so far. Dead chuffed I've actually started the build proper

 

Edited July 15, 2017 by Astrokev

[Jannis]

Looking really nice so far!

As far as your 280mm pier, i would make it thinner at the top. I learned it the hard way after just testing the HEQ5 mount and Explorer 200 scope on my 250mm pier yesterday. I thought 250mm would work fine all the way up, but i regret that now. It still works, but i can't leave it unattended. 

[Astrokev]

A few pictures of today's progress.

The sun parasol doubled up as a huge umbrella today, which was very useful when the heavens opened for about an hour this afternoon. Managed to keep the area I was working on reasonably dry, but I got soaked moving the mixing tray and other bits out of the rain!

Finished the second foundation block - this is the corner which will eventually be the scope room (bit of imagination needed here!). Two down, four still to do (I haven't made forms for the 5th and 6th blocks yet - I will re-use two of the corner forms once these are dry). The 5th and 6th blocks will go midway along the long edge of the obsy).

Mixing concrete has reminded me that I'm not as young as I used to be . I'm definitely going to have to borrow a mixer, or get a pre-mixed load delivered, for the pier block.

 

[Astrokev]

After a week of pretty good weather, why do the heavens always open on the weekend?

Between gaps in the showers, I managed to finish off the concrete work for the remaining 2 corner footings. #3 looks a bit of a mess as it started pouring down yesterday just when I was mixing the last load of concrete. I just had time to throw several empty ballast bags over the block to keep the rain off as it dried, which left imprints in the surface. I've checked today and the surface is smooth enough though. Today I did #4, which went OK.

So, here's the exciting pictures of footing #3 and #4 from today, and a wider view of the whole site - looks a bit of a bomb site at the moment!

Next job is to remove the forms and re-use 2 of them for the final 2 footing blocks, which will be in the middle of the long walls. This will probably be next weekend.

How long should I leave the forms in place before removal? Is one week enough ?

[Bizibilder]

Looking good - A week should be more than enough for ensuring they are fully "set".

[smudgeball]

I struck my formwork after a week.

I kept the outer damp with hose spray and cover prior to this.

It was fine when the frame came away.

Mine was for a pier footing so deeper than yours but it came out ok and I'm happy with the result.

Neil

[Astrokev]

Today I removed the forms from the corner foundation blocks , and then measured the four sides, and the diagonals, to see how accurate the dimensions turned out.

 

The 2 long walls were 9mm out. One was spot on at my target 3500mm, the other 3509mm

The 2 short walls were 6mm out. One was spot on at my target 2300mm, the other 2294mm

The diagonals surprised me, being only 2mm out! (4190mm and 4188mm).

Overall I'm pretty pleased with the accuracy , which shouldn't cause me any problems, as I can overhang the floor joists by the 9mm and 6mm to make the base nice and square.

 

Edited July 29, 2017 by Astrokev

[Astrokev]

Next job is to make the foundation blocks in the middle of the two long walls to give extra support to the floor joists and spread the weight of the obsy a little more.

I used the orange marking line to try and get the form aligned (I reused one of the forms I'd used for the corner blocks), levelled the form with my trusty spirit level, then fixed the form in position with 4 pegs hammered into the ground. Of course, having got the first block ready, the heavens opened and it didn't stop raining for the rest of the afternoon. Rain stopped play (again)

 

Edited July 29, 2017 by Astrokev

[Bizibilder]

That's good going for keeping things "square" - well done.  When you do the two additional blocks make sure that they come out equal or lower in height than the others - definitely not higher or you will discover that you have re-invented the see-saw!!    Packing the central block if required will be far easier.  Onwards and upwards 

[Astrokev]

Thanks Roger.  Sensible idea about the middle block - I finished concreting this today and certainly tried to do that . I guess I'll have to wait till I buy the joists to see how well I did.

Here's an image of the finished block.  I decided not to put metal strapping in this block. I think having the ends of the joist fixed only to the corner blocks should be sufficient. Rain forecast for later this afternoon, so polythene sheet at the ready!

Five down, one to go! Getting a bit tired of concrete to be honest and can't wait till I start on the woodwork.  I'm going to have to get a mixer for the pier block; I think it'd kill me mixing that amount by hand!  I need to decide whether to hire, buy second-hand off flea-bay, or try and find someone to lend me one.

 

 

Edited July 30, 2017 by Astrokev

[Astrokev]

Footing block #5 finished .

Torrential rain this afternoon so decided not to start on the last block - maybe tomorrow.

 

[Astrokev]

No picture tonight (getting a bit dark out there) but the good news is I've finished pouring all 6 footing blocks.

Looking forward to the weekend when I can unveil the last one.

Next step is digging out the hole for the pier block. This will be too large to mix concrete by hand, so will have to use a mixer. My son reckons there's a chap in the village who may be able to lend me his, so fingers crossed.

I also need to give some thought to how I'm going to support the air con duct tube in the right spot and at the correct height. Looking forward to this bit, as I'll be able to start cutting some wood!

Edited August 7, 2017 by Astrokev