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Thanks Wim. I can't claim much credit for the design I'm afraid. I've pinched loads of ideas off other builders over the last few years. Most of the design is based on the build YesYes did a few years back. Kev

So, didn't get as much done this weekend as I'd hoped for. Travis Perkins were able to sell me some lovely rebar yesterday. After finishing all my chores today I managed to find an hour this afternoon to start to fix the rebar in place. Here's a SketchUp drawing of the plan for the rebar - basically, 3 lengths driven into the surrounding ground from the block, then 3 longer lengths forming a tall pyramid to strengthen the pier tube. The air-con tube I'm going to use will rest on 500mm horizontal rebar attached to the legs of the pyramid. The brown pieces in the drawing are the wooden frame around the hole to which I'll screw a top sheet of ply to stop the concrete spilling over from the weight of the concrete in the pier. In the image I'd only managed to attach 1 of these support pieces before the rains came (again - I'm beginning to wish I'd built the obsy in the winter when the weather should be better ). Will attach the remaining 2 horizontal supports next chance I get. Then I need to make a wooden frame to support the tube laterally to ensure it's vertical. Once filled with concrete, the tube will be pretty heavy, so need to make sure the wooden frame is up to the job!

Thanks Adam. If the finished obsy looks half like the SketchUp drawing I'll be happy! I'm sure something will crop up that requires some re-design, but so far so good :-) No idea how long it will be before it's finished. I'm tending to do a bit each weekend, working around chores, family commitments and work. So long as I make some progress each week I'll be happy. would be good to get it finished before winter though!

Haven't posted a picture in a while, so here's a screen grab of my SketchUp design (minus cladding of course). Hopefully the finished build will look pretty close to this My SketchUp model has all the main elements of the build on 13 different layers, with everything dimensioned. This has proved really useful so far in serving as the blue-prints to take all my measurements from.

Indeed. Frost isn't really a major risk. I live quite close to a river so, although the garden doesn't flood, the water table is probably quite high. I'm not sure there's much I can do about this. I don't want to move, and re-routing the river is probably outside my budget ;-) I've taken on-board the various comments and think hammering rebar into the ground in the hole before filling with concrete should be effective at reducing the risk of the pier moving if I accidently bump into it in the dark (in addition to putting rebar in the pier, as suggested). The image I have in my mind is like a radial root system of a small tree or bush. Having had to dig-up several of these over the years reminds me how solidly the trunk is held in place by only 4 or 5 main roots radiating out into the surrounding soil. Kev

I'm afraid I tend to over-engineer most things DIY, so plan to use rebar in the block as well as the pier. Being at work during the week really drags out the progress . I've found it surprisingly difficult to find a store that sells rebar - Wickes and B&Q don't seem to stock it. I think the local Travis Perkins may have some, so off there on Saturday. Also need to order delivery of endless bags of ballast and cement - too many to carry in the car without using up a tank full of diesel! Also need to find a concrete mixer. Local hire shop may be the answer if I can't 'phone a friend'. Looking forward to the next stage. It'll be hard graft, but the end result will be the first bit of my build that will be visible when the whole thing is finished! Kev

After removing the shuttering from the last foundation block, today saw me start on the pier. First came digging the hole. I decided on a 750 x 750 x 750mm hole for the pier block. This was harder than I expected. After the heavy rain recently, the ground was soft enough, but it was difficult to wield the spade once the hole got below about a foot deep! Ended up using a garden trowel to scoop up the last bits of soil into a bucket. I was also getting close to the water table, so it was really sticky down there. Glad to finish it! Here's a few pics of today's progress. I now need to figure out how to hold my air-con tubing in place, and at the correct height, before filling with concrete. What have other folks done to achieve this? I'll probably use some rebar (when I find out where to get some from) hammered into the ground to try and create more anchorage for the block. Not sure if this is necessary, but I reckon better safe than sorry.

Tell me about it! I hand mixed 30 bags of ballast + 6 cement for the footings - spread over several weekends mind! All over now though - hooray!

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!

Footing block #5 finished . Torrential rain this afternoon so decided not to start on the last block - maybe tomorrow.

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.

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)

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.

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 ?

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.

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

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

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!

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!

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

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

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