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Time for a new Obs!


SnakeyJ

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Not much accomplished this weekend due to kids football and parties, but I did manage to order some 18mm shutter board for the 'table', 5 sheets of 4mm ply for the base skins, gorilla glue and pick up my brother's table saw.

I ran some batton through this as a test to gain confidence and check the bend radius of different thicknesses.     Batton will not be the final choice for timber as it is pretty horrible and very notty!    I also discovered that the saw fence was out of true and I was cutting a nice wedge profile  - though this can be easilly adjusted.    I think something just over 1/3" or 8mm will be a good thickness for the curves, reasonably easy to bend and will reduce the number of lathes required to build up the profiles.   The saw has a nice fine blade, wasting about 1/8" or just under 3mm per cut and I could comfortably get four lathes from 2" width.

I now need to source some better timber at a thickness of around 3/4" (19mm) - I'm thinking I will use the same thickness for all of my curves and will just sand back the outside edges of the ribs to keep the domed profile.

Not football next weekend, so with fair weather I hope to start laying up!

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When you start to cut your timber there will be a nice dry side and where the timber goes through the table saw a sappy side although its kiln dried it will bow as the sap expands the grain, until there used lay then on battens clamped together with a air gap to help them dry out a bit, or they will bow and twist......

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When you start to cut your timber there will be a nice dry side and where the timber goes through the table saw a sappy side although its kiln dried it will bow as the sap expands the grain, until there used lay then on battens clamped together with a air gap to help them dry out a bit, or they will bow and twist......

Thanks Tinker, my uncle suggested cutting and using them straight away to minimise this - the Gorilla glue shouldn't mind a little sap/damp to help it react.  Or do you think Kiln dried timber might benefit from a little old fashioned seasoning before use?

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I think the gorilla glue require one side of the joint to be wet, i would use PVA as its cheaper and 2 dried pieces of timber glued with PVA once the stuff has set, you will break the wood before the joint,,,,go on you know you want to try it,,,give it 24 hours to dry.....no joints will like opposite grains glued better a proper joint or screws......

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I think the gorilla glue require one side of the joint to be wet, i would use PVA as its cheaper and 2 dried pieces of timber glued with PVA once the stuff has set, you will break the wood before the joint,,,,go on you know you want to try it,,,give it 24 hours to dry.....no joints will like opposite grains glued better a proper joint or screws......

Thanks Tinker, I will have a test with some PVA - though was a little bit concerned about the longevity of this in a damp observatory.   It would certainly be easier to work with and no black hands either.

I'm going to use 3/4" planed softwood (white/red), or 21mm if my timber merchant has it.    A little more expensive, but working on 1/3" lathes I will need just over 300m, or about 30m of 19-21mm x 120.   Should be around £ 50-60, which does not sound too bad in comparison to the cost of ply.    I'll annoy the timber merchants by hand picking all the decent clean straight grained stock!

The weather's not looking too clever for the bank holiday weekend, so I may have to get a start on this during the week.

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If they stocked good timber you wouldn't need to pick and choose, i do the same even if it 19mm T&G for a gate no point in have the warped, knotted timber that was a tree last week.....starting the build the sooner the better......

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Well the 2 x 18mm ply (layup table) and 6 x 4mm ply sheets for the base skin and door, came in at £ 137.    Redwood timber for the lathes (21mm x 70mm and 21mm x 190mm) came in at £ 97.   This leaves a mere £ 46 in the budget for covering and painting the dome, wood preservative/sealant and something to run the shutter on.     Never mind, it's payday tomorrow :)

I routed out the best grained timber I could find, though will still loose some due to knots and minor shakes.    Hopefully there will be enough to do the job and save another wallet bashing!

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I completed the table/rig for layup this afternoon, marking up a radius of 1050mm for the base rings and fitting 8 outer blocks of 21mm timber with batton toggles to prevent the lathes lifting up.   Inside of this I've cut 8 snail cams to clamp the work up.

I cut 10 lathes of 1/3" thickness to test the layup with a dry run, these lay in nicely but I was working from a shorter piece of timber (2.5m) and I need just over two and a half lengths to get the outer circumference which is less than ideal.    My circumference for this will be 6597mm, so it will be impractical to run this from a single length, but I can do it from 2 x 3.3m lengths which will be much easier - the shorter lengths can be used up once I have got the first two laminations, with the joints offset.

The dry run was a useful exercise, proving the lathe thickness and clamping ideaI, though showed that there are not enough points to hold the form - some bulging out.     I will double up on the clamps from 8 at 45 degrees to 16 at 22.5 degrees - I was using off cuts of gravel board for this, so the timber was negligible cost.      Although I could manage with the table saw, I will also build a table to support the longer planks as I cut these.

Otherwise a positive test.    Sadly the weather is not looking to good over the bank holiday weekend, so not sure when I can next spend a few hours on this - but hopefully I can at least get the clamps done and fitted :)

I saw a 2.1m Pulsar dome on ABS for £ 950 (now sold), a little too far for me to travel, but I was seriously tempted for a moment ;)

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Sadly no further progress on the obs over the bank holiday as I had other, more important, gardening duties to perform.     However, the garden is looking much neater, the lawns have been fed and dressed, flower beds dug and planted, summerhouse 'jacked up' and levelled, gutters cleared and numerous other pifflings.   It was nice to be out in the garden and I've earned lots of brownie points for next weekend - hope the weather improves by then ;)

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Euwww, gutters.  I need to clear ours out, but at three storeys high and then some I'm not so keen :(

James

Bamboo might be in short supply, but you could experiment with coppiced willow!

post-26731-0-16365400-1430822029.jpg

Certainly not for the feint of heart ;)

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  • 4 weeks later...

I've been having some issues with the laminating table/former, which was not holding providing sufficient external form to hold the outer lathes with 8 limits/clamps.   I decided to double up and try with 16 points, but the result still not sufficient for my dry layup.

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I think it would work if my lathes were long enough to do the entire circumference is once piece - but this would be impracticable with circa 6.5m lengths of timber to saw!

I think I will buy a sheet of mdf, cut strips from this to fix around the entire circumference and then use a router and trammel to cut the curve former in this.    If I make the smaller diameters first and leave sufficient width to work with, I can work my way out by growing the former.     The snail cams work well and will be re-used ;)

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Can you preform them in some way Jake so there's not as much strain when you fit them to the final shape ?

Just each end on a block and some weight in the middle maybe.

Maybe dampen them, after a while they will stay curved.

Dave

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I really admire you guys who built domes :)  A roll-off-roof shed was plenty for me :D

Thanks Gina, though I've yet to complete the build and deserve any accolades!     Then again my first build was a simple resurrection of Roger's (Bizibilder's) original observatory, so this is really my first design and build ;)

Can you preform them in some way Jake so there's not as much strain when you fit them to the final shape ?

Just each end on a block and some weight in the middle maybe.

Maybe dampen them, after a while they will stay curved.

Dave

Cheers Dave, no problem bending them to this radius and it's quite manageable doing this single handed.   I've only had a couple of breaks, where the timber has been knotty.         The issue is accurately holding the form of the outside radius, where I have fitted 2+ lengths of timber.    This needs to be pushed out in to a contiguous ring former, which I will rout from a ring of MDF strips.    I think this should make it much simpler and quicker to lay these hoops up.

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  • 3 months later...

So little time (and money) to progress this project over the summer, but I did manage to finally fit the pier in time for the lunary eclipse on Monday morning.

The pier bolted down on to the M16 threaded bar that was cast into the pier foundation and feels good and solid - here's a picture of the mount and Vixen 80m, which was used for a little white light solar as I was sorting out the electrics.

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I think I may just adapt an inverted dustbin or water butt cover, so that I can at least leave the mount fixed/aligned and possibly the electronics.     I could always seal this and bulk buy some desiccant to keep the humidity and condensation at bay.

Here's the western view from the pier this evening - stunning sky and nice open horizon, at least this aspect ;)

post-26731-0-70688900-1443555327_thumb.j

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  • 4 months later...

Had a few more important things to deal with over the last seven months, but although priorities are still very much focused in the present, we have had some good news which makes this project more realistic in the mid term.

When we moved last March we had a standard 12 month lease.  I learnt in October that the owner had lost her own battle with cancer and that her husband wanted to sell the house at the end of this lease.  Also in October my daughters health dramatically worsened such that we needed to buy and adapt our own house.   Suffice it to say that we've had our offer accepted, received a formal mortgage offer today and my mum has been able to provide the deposit.   Everything appears to be lined up and we're buying our house.

Inevitably cash will be in short supply for some time - but at least I can start looking out for the materials and build a permanent observatory.

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  • 1 year later...

Resurrecting an old thread - the long trailed 'new obs' is back on, though the DIY may be confined to automation of rotation and shutter.

 

Just acquired a s/h pulsar 2.2m dome and ready to enjoy the dark nights of winter ?

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