Dome & Wall Ring Sub-assembly

Having cut out all 32 x 45degree sectors for the dome ring and wall ring out of 8 x 3/4" sheets of hardwood marine ply, the sectors were glued and screwed together in groups of three, offset to lend maximum strength and support to each other, with each sub-assembly representing 90degrees of the full ring.


After gluing and screwing the three sectors together into a double thickness of 3/4" ply, a small forest of G-clamps was used to squeeze out the excess glue and assist in a uniform laminate.

Laying this lot out on the ground, in a full circle, gave me a real sense of just how large a 16' dome was going to be! Man, this thing is big!! It was gratifying to see that my trigonometry skills haven't completely deserted me - all the sectors were exactly the same size - to the millimetre!

Cutting the Dome Rings

To support the lower rim of the dome, lend it more rigidity, and provide a hard flat surface for the dome transport wheels, I cut out out 16 x 45 degree annular sectors of 3/4" marine ply that will be glued and screwed together to form a double thickness (1.5") ring. This Dome Ring has an outside diameter of 2500mm, exactly matching the outside radius of the dome itself, and is 150mm wide.

Another, double thickness ring was similarly cut and will be attached to the top edge of the octagonal observatory walls. This Wall Ring is 50mm smaller in diameter than the upper dome ring, allowing the dome ring to overhang the wall ring by one inch all round. The wall ring is also wider than the dome ring, at 330mm, so that the eight outside corners of the walls are aligned with the outer circumference of the ring and the inner corners with the inner circumference.

At a later stage a thin, 6" wide metal strip will be attached to the outer edge of the dome ring. This strip will hang down below the wall ring and prevent rain from being blown into the gap between the rings. A draft-excluder brush strip, as used on the bottom of doors, will also be attached to the outer edge of the wall ring with the brush pointing up and gently rubbing against the dome ring to keep out insects and dust.

Using graph paper and compass I experimented with how many sectors I could cut out of each sheet of ply. The best fit was achieved with two dome ring sectors and two wall ring sectors nested tightly together. My 10:1 scale drawing suggested that I should have 30mm to spare... however, my pencil lines and slightly springy compass meant that my error factor was a little over 30mm! Cutting the first sheet was going to be an act of faith!

10:1 scale drawing of how two dome rings and two wall rings

fit onto a single sheet of 4' x 8'

Eight sheets of 3/4" x 4' x 8' Hardwood Marine Ply are required to cut out the 32 sectors required for the two rings. For those who haven't had the joy of trying to handle this stuff, a single sheet is humongously heavy even for two men. Dragging this stuff around my yard and into the garage single-handedly for cutting nearly cost me my life on numerous occasions! My arms hurt. My back hurts. Everything hurts!!

Before cutting each sector, the two ends of the sectors were carefully defined so that they would be accurate 45 degree sectors. This was done using simple geometry... on a large scale!

I knocked up a long radius arm for the router out of a length of skirting board, using a screw as the pivot point. The plywood sheets are raised off the ground by some lengths of scrap chipboard to prevent damaging the cutting bit. Three passes with the router were necessary to cut all the way through the very hard 3/4" ply.

Slow progress... as you can see, there is precious little space between the cuts

every millimetre is precious!

And the proof of the pudding is in the cutting...

Full house - they all fit!!!

Dome Control Hardware

There are a number of commercial systems on the market to control the dome (opening and closing the two-door shutters, and slaving the dome to the telescope so that they are both pointing in the same direction.) However they are rather expensive for the piddling amount of electronics and driver software involved. I was just about to reach out and 'touch' a friend to see if he could weave his magic (and soldering iron) to come up with his own control system, when I stumbled across the LesveDome group, run by Pierre de Ponthiere, who had developed dome control hardware based on a generic off-the-shelf USB controller board. The USB board is used to control a number of power relays for activating the dome shutter and azimuth motors, and to take inputs from a number of sensors and limit-switches. The ASCOM compliant driver software is still under active development by Pierre but is fully stable in its present incarnation. It's also dirt cheap!

There is a registration fee of €30 for the driver software (after 60 days free trial) and the USB controller board can be picked up either ready assembled or in kit form for around €56 including shipping. Being a consummate fiddler, I plumbed for the kit, which looks like this:


The kit is a doddle to assemble for anyone who can wield a soldering iron safely without putting out one of their own eyes or accidently setting fire to the cat, and requires no knowledge of electronics. After sorting out all the components and checking that nothing was missing, thirty minutes saw the unpopulated circuit board transformed from this:

...into this:

The kit comes with a CD of interface software for general use and for testing the completed board. I bought the USB Interface Board Kit from Ramsey Electronics in the USA using PayPal and had it in my hands less than a week later. Excellent service!

The next step is to knock up a small circuit board with the power relays and other ancillary gubbins - more on that later.

Full Size FSP Layout

To double check the final dimensions of the Folded Stevick-Paul optical tube assembly I laid out three 4'x8' sheets of plywood on the ground and drew out the optical path at full scale. The white rectangles in the photos are full scale drawings of the mirror cells that will be bolted onto the tube assembly. Doing this allowed me to double check all the dimensions and angles that I would need for cutting up the 1" box-section steel for the OTA and fine tune the whole support structure.


The photo, below, shows the light path of the convirging cone of light to its focus point, and how it passes close to the tertiary 10" flat folding mirror (in fact, through it's cell!) This mirror cell will have to be built in such a way so as not to impede the light path. Cooling fans on the tertiary mirror will heve to be ducted away from the light path to avoid turbulence.

It is interesting to note that in faster (f/12 and faster) versions of the Folded Stevick-Paul design the light cone actually grazes the edge of the tertiary mirror, which needs to be very carefully bevelled to minimise the obstruction. This is another reason I decided to design my FSP at f/15. I had hoped to make an f/20 system, but that would have meant building an even bigger observatory! Also, I can *just* test a 14" f/15 mirror inside my house. The mirror must be tested at its radius of curvature (twice its focal length) which is 10.5m!!!

Sub-Assembly

1st May 2008: Wonders will never cease! After something of a hiatus, I finally managed to pull the finger out and start work on this project again!!! I finished off nailing and gluing the 2" edge support ribs to all of the hex-pents and drilled them to accept two M6 gutter bolts to assist in joining the panels together for final assembly. Stone me - it works too!! Using bolts to hold the panels together while the glue sets removes the need for lots and lots of G-clamps (been there... and gave up!)

To make final assembly of the complete dome a little easier, I have glued and bolted together five sub-assemblies consisting of a central pentagon surrounded by five hexagons. These sub-assemblies are about as big as can be easily lifted and carried by a single person (i.e. me!) They will eventually be joined together with five sets of intermediary sub-assemblies (middle picture, below.)




My next move was to cut out the 4mm plywood for the inner skin of the dome, to hide all those nasty looking support ribs and provide a smooth inner surface to the dome to facilitate heat to escape through the open shutters. Without a smooth inner surface, the ribs would effectively provide lots of pockets for warm rising air to get trapped in... which would result in a slower cool-down of the observatory and ultimately, crappy seeing.

Internal Support Ribs

Although geodesic structures are inherently strong I wanted to strengthen the Hex/Pent panels around their periphery with a 2" wide strip of 1/2" ply. This would also make final assembly much easier (i.e. possible!) when it came to joining the panels together. The ribs also allow an inner skin to be fixed to the inside of the dome giving a nice contrast in geometry - outside you have 360 triangles - inside you have 55-odd hexagons and pentagons! More importantly the ribs offer something for the shutter-opening brackets/hinges/widgetry and motors to be bolted to, without going through the outer skin.

Each rib consists of a 2" wide strip of 1/2" ply. Both long edges must be cut at an angle unique to the triangle edge that it is supporting (I cheated here and fudged the angle at 4 degrees as the actual difference in this angle for all the different triangle edges only varies by about 0.6 of a degree. Life's waaaaay too short, so sod it!) I used a borrowed table saw for this job, cutting up around four sheets of 4'x8'x1/2" ply into 8' strips. The saw blade was set to 4 degrees off verticle.

The ends of each rib must be cut at TWO specific angles simultaneously if they are to fit together accurately and offer maximum support to the panel as a whole. A mitre saw, a drill-bit and a little trigenometry can overcome this minor headache reasonably well. Doing this by hand, however, was a major pain in the bum, so after struggling through about half of the ribs with the hand mitre saw I invested in a power mitre saw on which I could set the angle and tilt of the blade. The blade on this saw did not cut as neatly as the hand saw, but it made short work of the remaining ribs.

The ribs were then glued and nailed to the inside edges of the HexPent panels and clamped tight around their periphery with a ratchet strap while the glue cured. The ribs remove a lot of the flexability in the panels and add a lot of strength to each panel and the whole dome assembly.

Hexagons & Pentagons

Assembling the Hexagons and Pentagons.
Now a 6v icosahedron dome is made up of 360 individual triangular panels, but to make on site assembly of the dome a little easier these triangles are first glued together into six (purple) pentagons, ten (yellow) hexagons, 30 (blue) hexagons, ten (green) hexagons and ten (green) half hexagons... which themselves come in two different flavours!

How the panels fit together (detail of 1/5th of the dome.)
A 6v icosahedron dome is made up of six pentagons and 55 hexagons...
which come in three flavours.
Be very, very, very careful to assemble them in the correct order
if you want to avoid severe mental trauma!

To avoid using miles of duct-tape to hold the triangular panels together while the glue is setting (not an effective solution... as I discovered early on!) I knocked up a jig to hold all the panels in place and clamp them tightly together. The jig consists of a number of support ribs; one for each glue joint between two adjacent panels, and a self adjusting peripheral clamp to hold all the panels in perfect mutual alignment while the glue sets. Unfortunately the jig doesn't do a very good job of self-adjusting and so I found it necessary to pre-align the jig and panels before gluing. Once aligned, all the panels are removed, with great care not to move the jig or support ribs, and glue applied to *both* edges of every panel before once again placing them back in to the jig without disturbing it. The glue I used is an exterior and marine grade wood glue, suitable for joints that will see prolonged immersion in water (i.e. boat building.) It is a water-soluble (while wet) white PVA type glue, so you can easily clean up with soap and water. I picked up a 5ltr jerry-can for about 40euros.

Despite my best efforts to cut the panels to an anal degree of accuracy, small gaps sometimes appear (due to uneven tensioning of the jig or slight warping of the panels) and I found the easiest way of dealing with these was to *not* wipe off the excess glue that was squeezed out of the joins, but allow it to shrink back into the hair-line cracks as it cured. After 24 hours of drying there is actually very little excess glue to be sanded off - It all seems to be absorbed back into the join very nicely. A note of warning to the impatient (like me!): Although the glue will *probably* be set within 12 hours, I found it necessary to leave it at least 24 hours before removing the tension from the jig. I cocked up royally God knows how many times in the beginning by taking the early hex/pent panels out of the jig to admire my handy work... only for the glue to fail while I was removing the excess. Elation quickly turns to a Homeresque D'Oh! Be warned!

Cutting out the support ribs for the assembly jig.

The Ribs are screwed to a central hub and centred inside the assembly jig.

Panels are first layed out and aligned in the jig to ensure a perfect fit and alignment.

Panels are then removed and glue applied to both edges before

being re-inserted into the jig. All edges and corners must be aligned

with each other with great care.

Once all the panels are glued, gentle tension is applied

to the jig and a weight placed in the centre.

Great care must be taken to align the corners of all the panels exactly.

The excess glue is not wiped off. It will tend to shrink back

into the join and help fill any gaps.

Beginning to take shape - Triangles into Hexagons & Pentagons

The Finished result!
(note the different sizes of hexagons)

Health & Safety

A Gardening accident that happened in the air...

14th October 2006 - With all the triangles cut out and bevelled it was time to start assembling them into their respective pentagons and hexagons - but first I had to make time for a little serious work in the garden. Having filled in the 150m trench along the garden path, the soil had subsided a little (as anyone who has burried a body in a shallow grave will know) and needed to be re-filled and leveled out. I spent the morning raking extra material into the long depression, piling it up a couple of inches before rolling it down with a very heavy garden roller. Now dragging this monster up and down the garden path was absolutely knackering work, and by 3 o'clock my arms were several inches longer and I was ready to collapse. As luck would have it, a friend called me to say he was going flying at a local site and was I interested. I didn't need my arm twisting, so I downed tools, loaded the glider onto the car and headed for Killiney Hill.

Flying Hang Gliders at Killiney Hill, 14th October '06

To cut a long story short, we had a lovely evening flight and I was just lining up the glider to land on the beach in the dusk when my right shoulder dislocated with a sickening crunch while I was manoeuvring the glider onto finals. I managed to land the glider with just one arm but renched the dislocated shoulder badly when the glider came to a stop when I had to drop it... and suddenly I was in a world of pain! Anyway, torn tendons and nerve damage put the kybosh on all work for the next nine months while my arm was in a sling and receiving physio. X-Rays revealed that I had managed to yank my arm a good 2.5" out of its socket! Bummer.


Interlude and Twiddling of Thumbs.
By the end of December the damaged nerves in my shoulder were starting to repair (painfully!) and I was able to start using my arm again to some degree. Having pulled most of my hair out with my left hand over the previous few weeks of enforced boredom, I figured I might as well knock up this website and do a little detailed design for the mount and telescope tube.
It's probably worth mentioning a little discovery I made around this time - namely that pills and booze are a wonderful combination for killing pain, dulling the senses and making the real world go away... which may partly explain the general tone of these pages! The down-side is that reality always comes marching back to goose-step all over your cosy little fantasy world like an invading swarm of storm troopers in the cold light of morning... and as for the big nasty bright thing in the sky, we hates it, we hates it; it hurts our eyeses!

Bevelling the Triangle Edges

Bevelling the Triangle Edges

With all 360 triangles now cut out and their edges marked with their lengths (this is essential to avoid disaster later!) I now had to trim each edge of each triangle to a particular bevel angle, so that they would fit together neatly, without reducing the size of the outer face of the triangle. This calls for some very accurate angles and very careful cutting. I knocked up a jig to clamp each triangle in place and hold the router at the desired angle while it trimmed the edge. A little simple trigonometry, a couple of gutter bolts and a vernier calliper allow the angle to be set very accurately. By the way, that's 1080 edges that have to be bevelled to a truely anal degree of accuracy... who's stupid idea was it to build such a complex dome? Gnrrrr....

Dihedral / Bevel cutting jig:

Each triangular panel is clamped down to the work surface...

...at a very specific distance from the hinged edge of the jig
using a removable spacer with adjustable screws.

The spacer is then removed...

...the router-slide swung into place and

the router run across the work piece.

Dome Fabrication

September 2006
Started cutting up the 22 sheets of 6mm plywood for the
outer dome skin using a router and a few jigs.

A router, in a slide clamped to the wood was used to cut
the 4'x8' sheets of plywood into narrow strips.

The width of the strips is the *exact* height
of the triangles that will be cut from it.

With all the strips cut to size, they are then carefully marked
out and cut into triangles to sub-millimetre accuracy.

Marking was done with a sharp Stanley knife.
360 triangles were cut out this way.

The 4'x8' sheets of marine ply are first cut up into strips whose width is the *exact* height of the triangles you want to cut out. Each strip will yield 3 or 4 triangles. Next, a master template triangle is measured out to sub-millimetre accuracy using a sharp Stanley knife to score the wood and cut out using a router with a fresh bit. This master template is then used to mark out all the other triangles for that group. Simply place the template down on the plywood strip and align it with a straight edge and then score along the edge with the Stanley knife to mark out your next cut. With care, you can mark and cut your triangles to 0.25mm accuracy without loosing too much hair. After cutting out each triangle, it is compared with the master template again to check for any deviation and can be trimmed using a trimmer bit in the router at the end of each batch. This was only necessary a couple of times!

Artifice & Edifice

Grand Designs (and general silliness)

This is the story of a dream... or perhaps a flight of fancy, to build an observatory to look at the stars - a latter day cathedral of light! Most sensible people discount dreams as random nonsense thrown up by the thinking prune during yawny-sleepy-snoozie-snooze time... With hindsight, there might just be something to that!

To be read with a large whiskey in hand

and an even larger pinch of salt...
for that is how it was written!

Irationale:
Peed off with burning so much petrol driving to and from dark sites; loading and unloading the car; setting up and breaking down the telescope, and lugging all my equipment half way around the country, only to have the clouds roll in just as I'm ready to start observing (sound familiar?) I figured the only way I would get any good observing done was to have the scope permenently set up and ready to go.

This meant having an observatory.

Need & Avarice:
Now, my main instrument at the time was a 20" f/4 Newtonian, but I figured that if I was going to have to build a mount (equatorial, motor driven and computer controlled, of course) capable of carrying this beast, I might as well make it bigger so that I could mount a few other bits'n'bobs as well.

Now, what I really, really wanted was a high contrast planetary scope for doing solar system photography, photometry and astrometry, and as I kinda liked the idea of having an odd-ball instrument I designed and built a 14" f/15 unobstructed Folded Stevick-Paul tilted component reflecting telescope (phew!)... (which gives amazingly sexy images with a total lack of aberrations that is just to die for!) and used this as the basis for the dimensions of the observatory. Also, with a little jiggery-pokery, I could turn my 20" f/4 Newt into a 20" f/24 Loveday... just for a giggle! This would mean extending the tube a tad to accommodate the extra reflective surfaces needed for this Frankenstein transformation.

Here's the optical path layout for my 14" f/15 Folded Stevick-Paul
(make of it what you will - wierd, huh?)

Form and Function:
Now, the 14" Folded Stevick-Paul instrument is about 10’ long, and with the 20” Newtonian piggy-backed on that, (ha! nice throw-away line, that!) I reckoned the observatory needed to be about 5m in diameter (don't you just love it when I mix Lbs, Shillings and inches like that!) so as to give me enough room to move around comfortably and not have my body heat create the dreaded ‘dome effect.’ Did I mention I always wanted a domed observatory? No? Well, it was a given as far as I was concerned. Technical aspects aside, I always wanted a dome, so a dome was what I was going to build. Domes are cool, and a 16' dome would elevate my ego well above the unimaginative poxy little garden-shed-run-off-roof-DIY jobs that most amateur astronomer wannabees fertively aspire to with their miserable "Oh-I-haven't-got-enough-money-for-a-real-observatory-and-what-little-I-do-have-I-have-to-spend-on-the-wife-or-she-won't-shag-me" dream castrating negativism. Me; I don't have that problem (no wife, no kids (that I know of), no worries) though my ego has been known to over-inflate occasionally and I try not to cramp its style... especially when I'm half sloshed and drugged up to the gills, like now! A little room for expansion (for the telescopes, of course) is always a good idea! Ok, ok, I realise that in the real world other factors have to be considered when designing your dream star-palace. Space is usually at a premium (ironic, or what?!) and 'er indoors needs room to string a washing line to hang up her undies, but I can't help thinking that compromise is the cancer of creativity. I mean, come on, can't she use the laundro-mat? Not that she *needs* to wash any clothes... judging by the credit card bills and it's not as if *she's* going to build anything in the back yard, and anyway, the less grass that has to be mown, the better... mutter...mutter... Come on, grow some balls, men. Just who pays the mortgage in your house anyway? Hmm... on sober reflection, life is short and taking a stand like that might just shorten it a lot more! Best stick with a converted garden shed. After all, what sane woman would deprive her man of his shed?

Location, location, location:
Casting around for a suitable location to site the observatory was not as straightforward as I thought. Although I have a large garden and lots of land around the house, the best (aesthetic) locations were either swamped by flood lighting from a neighbouring waste recycling centre (vermin and scum of the universe – not recycling in general, just this particular lot) or had too much of the sky obstructed by the very tall, mature trees surrounding the property, or were compromised by the boiling plume of heat rising from the totally un-insulated stately pile I call home. Bummer.

My environmentally friendly neighbours (a.k.a. Scum of the Universe)

To be fair to the Scum of the Universe, they did take (some) action when, after arriving home after 1am one night, I found that I was able to read the newspaper in the light from their plant *reflected* off my house! I totally lost it and fired off a super snotty letter to their general manager cc'd to the EPA. To their credit they were knocking on my front door at 9am the following morning! Grudging respect for this one instance aside, they remain the Scum of the Universe as long as they continue their antisocial activities and string along the local residents with false promises. Varmints!

Throwing your rattle out of the pram really gets results... sometimes!

That left a small plot bang in the middle of the flower garden. I anticipated some resistance from the family. Then a cunning plan began to form in my devious little mind.* I could sell the idea if I lied outrageously about the true size of the observatory and told them it could double up as a garden summerhouse – you know; nice place to sit out; tea in the garden; tweetie-birds; flowers; the whole nine yards. Once it was built and they saw the actual physical size of this monster; if they still didn’t like it, well… yaa-boo-sucks!

[* It’s not often you come across a small, or indeed devious little mind residing in the same head as such a large ego. The universe is a truly wonderful place!]

Where did all the peanuts go?
(or... reality revisited!):
A fairly major part of my cunning plan was to equip the observatory with a really cunning disguise, a sort of cloaking device that would render it almost not entirely blindingly obvious to the casual glance by a half blind person enjoying the garden after sunset... and to the CIA with their pesky little satellites flying overhead... by covering the dome in sheet copper treated with carbonic acid to turn it green. I reckoned that this would help it to blend seamlessly into the background, (yes, I know – it was a lame idea thinking I could hide an elephant under the carpet and hope no one would notice) but the real show stopper for this idea was the price of copper. I nearly had a heart attack when I priced the amount I would need – it still gives me the willies now, just thinking about it!

Ok, arse to that idea – it was going to stick out like a sore thumb and there was nothing I could do about that. Perhaps I can camouflage it with vines or something. Whatever.

Mine, all mine!
Anyway, the site I selected offers a 360°, mostly unobstructed view of the sky down to 20° above the horizon – not bad at all – and I put a mental CPO (compulsory purchase order) on that particular bit of the garden real estate… which was unused and a bit overgrown anyway. I’d be doing everyone a favour by tidying it up :-)

360° panorama from the observatory location in my garden. Note: the sun is at 19°51' above the horizon (11h51m on 9th November 2006)

Just to make doubly sure that no one else got any ideas about that part of the garden, I dug it up in the dead of night and hid it!

To build an observatory: First dig a big hole... then fill it with your money, dreams and sweat!

The only thing going against this site was a brace of pesky street lamps… but I had another cunning plan up me sleeve (which I’m not going to share, ‘cos it’s a bit naughty!) All I’ll say is: Here’s to the Glorious 12th!

There are two ways to extinguish street lights: legally... and with fire arms!

Architectural Merits:
Right, time for a bit of design work. What form was this monstrous edifice going to take? Although I wanted a dome (domes look good – or did I mention that already?) I really didn’t want one of your traditional looking domes made up of curved ‘gores’ riveted together, and as for fibreglass – well, I suppose it burns nicely, but the less said the better. Sorry if that offends anyone, but these are my prejudice that are getting an airing here, so ya, boo, hiss and jumpety-jump! Go write your own web page!

I know, I thought, let’s go geodesic! Cool!! I cast around the net for info on geodesic structures, and lo and behold I got more hits than a 16 year old deb in a skimpy dress! Whittling down my search criteria, I did come across a few other geodesic observatories built from (amongst and of all things) expanded polystyrene covered with stucco plaster! I mean, why go to all the trouble of creating a really sharp looking geodesic structure... and then hide it under a layer of dried mud? I wanted mine to look sharp enough that you could cut yourself on it!

I decided to design my own, and plumbed for a 6v Icosahedron made up of 360 individual triangles… each of which would have to be cut by hand to sub-millimetre accuracy and with each of the three sides of each triangle bevelled to a unique angle to make it all fit together snug as a bug. You may (rightly) surmise that, as the prospect of all this masochistic work didn’t actually frighten me (too much,) I had loooong since ceased taking my medication. Sanity was now officially away on holiday with the faeries!

Oh, just in case you were beginning to get the (false) impression that I am in fact a mad genius whose brain is bulging from mathematical ability, let me disabuse you of that notion immediately. I didn’t do any mathematical calculations (no, not one, I tell you) while drawing up the plans for the geodesic dome (geodesic maths sucks!) I did try, but my nose strted to bleed when I couldn't find the 'ON' button on my calculator, so I gave up. Maths makes my head hurt somethin' rotten. No, I happened upon a most splendid piece of CAD software, Cadre Geo, that does all the hard work for you. I just plugged in the dimensions of the dome I wanted and the program spat out all the numbers followed by an error dialogue that simply said “Nutter!” It even drew me lots and lots of pretty pictures of the dome and the individual panels. Excellent!














Another useful web site dedicated to geodesic domes is Desert Domes which has an excellent calculator and collection of graphics. Yet another page http://obs.nineplanets.org/obs/obslist.html lists hundreds of dome and run-off observatories from which I pinched various ideas.

Quantity Surveying:
Ok, now I knew how big the dome was going to be, and its shape, it was time to work out just how much material I would need to construct it… and thus how expensive it would get. With polystyrene and fibreglass (cough, gag, spit!) out of the equation, I decided to use ¼” Baltic Birch Ply for the dome, covered with 0.7mm aluminium foil which I would glue onto the ply before marking and cutting out. Now ¼” may seem a bit thin and flimsy, but ½” ply would have been twice as heavy and twice as expensive (well, duh!) Anyway, some other fool had already successfully built a smaller geodesic dome from 4mm ply and it seemed to work just fine! Mine was going to be a whole 2mm thicker - I was guaranteed success!

Out came the graph paper, pencil and ruler and I started filling drawings of 4’x8’ ply with lots and lots and lots and lots of little triangles. When I was done, I reckoned I could get all 360 triangles out of 22 sheets of plywood. Uugh... the costs could get ugly!

Above: To lay out the panels on graph paper I first measured and cut out a template of each triangle using thin card and used this to work out the best rotational position of the triangles to achieve the best fit. Some sheets have several different triangle sizes on them, as above - 18 x H-type triangles on one sheet of ply with another 6 x H-type each on the space left over on sheets E and F. Pack 'em in and stack 'em high!

Another fly in the ointment:
Plan B was (note, past tense, for the unobservant) to glue sheets of aluminium to the plywood before slicing it up and then gluing and welding the ply and metal sandwich into hexagons and pentagons before assembling the whole caboodle on site. Unfortunately (again) my experiments in welding aluminium glued to wood did not yield the splendid results I had hoped for. Getting enough heat into the aluminium sheet tended to burn the wood and glue beneath it… weakening the whole structure. The best (and way the coolest) method I came up with is a welding technique called ‘Friction Stir Welding’ but, alas, it required tools somewhat more sophisticated than the router I was armed with and with which I had conducted a few experimental welds. The technique does work… but it was slow and the finish was not all that pretty. Anodising 22 sheets of 4’ x 8’ aluminium was also proving to be a bit of a problem. I could get it done commercially for LOTS of extra cash, but not in the colours I wanted. Realistically that meant the aluminium weather cladding was also out. Drat and double drat!!

Solution [preferably something that won't dissolve in water]:
This tactical setback meant that I was going to have to settle for a fall back solution (Plan C) to protect the dome from the harsh nasty Irish weather and the even nastier effects of the Sun’s UV radiation, both of which would dissolve Baltic birch and ordinary outdoor paints in short order, so out went the cheap nasty Baltic Birch and in with the most excellent (but much more expensive) Marine Ply. Swings and roundabouts, folks; with aluminium and baltic birch out of the equation and marine ply and uber-paint back on the menu, the costs added up to about the same.

An Interesting Statistic:
Now, Marine Ply (best illegally-logged Malaysian hardwood from virgin rain forests, of course, with free baby Orangutan with every ten sheets - I've now got three of the buggers swinging out of the lights and crapping all over my home!) has a density of 0.00511g/sqmm*, and the dome has a total surface area of 38,936,759.5sqmm (give or take a bit) which means that the outer skin alone is going to weigh in at 198.96kg… not including the ribs, the 4mm inner skin, dome ring and paint. Woah - that’s heavy - but at least the wind won’t blow it away!!

[ * yes, I really did cut out a 1sqmm piece and weighed it veeeeeery carefully using a tiny cocaine balance!]

Buckminster-Fuller meets Paintball
(or how to protect a Bucky-ball):
The reason for all this palarva (plans A & B - the copper and aluminium route) was that I didn’t fancy the chances of modern paints duking it out with the Sun. The Sun is big and hot and has a secret weapon (UV) that crisps most paints over time… even UV resistant paints and ghastly fiberglass! This unpleasant fact was repeatedly demonstrated to me every time we had the woodwork on the front of the house painted. Within just a few months of all that nice shiney, expensive paint going on, it would start to blister and crack and fade. Repainting it with the same modern 'UV proof' synthetic paints was just pouring good money after bad. It was also deeply depressing. So a few years ago I stripped all the paint off the house - right back to the wood (which was dry as a bone and gasping for nourishment) and applied my secret weapon!

I had read in Country Life Magazine that the Holkham estate in Norfolk, in the UK, was experiencing the same problems with their paintwork and had taken a gamble by going back to linseed oil based paints. The results were astonishing. After five years the paint was as good as new and by wiping it down with a fresh coat of plain linseed oil the paint would recover its original gloss and luster. I tried it on my house and got the same results! After several years, the paintwork is still in top condition and only needs a fresh coat of oil to brighten it up. The wood (which absorbed the initial treatments of plain linseed oil like blotting paper) has been given a new lease of life! One of the greatest benefits of linseed oil paints is that not only is it waterproof but it allows the wood to breath. So now you know; linseed oil is my secret weapon... it also smells great and leaves your hands beautifully soft too!

Walls, Doors and Floors:
After going to all that trouble to design and build such a splendid dome, it felt a shame just to leave it lying on the ground where it might get kicked and wet (and overgrown in my garden!) Lifting it off the ground with walls seemed to be a sensible idea... but how many? I thought about building just one wall (circular, you dummies!) but felt that was a bit predictable and boring. Two walls would certainly be different, but a bit draughty. Eight walls seemed a nice compromise - four for north, south, east and west, and another four to fill in the gaps.

The next major decision was how tall should they be? Silliness aside, I checked the local planning laws which permit an erection without requiring a planning application to be lodged as long as it is not more than 25 square metres in area and not more than 4m high. I was safe with the observatory's footprint, but with the dome rising 7.5' (with a 6" overhang of the walls) I was limited to a wall height of just over 5.6' unless I sank the floor below ground level. That actually worked out very nicely as the doors to my small greenhouse and the fern-house are both just over 5' high and require you to stoop a little to enter. It lends a quaint old-world feeling to the garden. The observatory walls and doors would be in keeping! I planned to build the walls out of 4x2" studs clad in T&GV planking on the outside and thin cedar strip on the inside. The floor would be T&G planking over 2x6" floor joists on 20" centres.

Bill of Materials:
With all the major dimensions worked out I could now draw up a list of materials needed to build this monster and work out just how much it was all going to cost me. This is where things get ugly and I began to get a crimping sensation in my sphincter!

Dome Construction Materials:
€431.73 for 8 x sheets 4'x8' x 18mm Marine Ply (for dome rings)
€460.53 for 22 x sheets 4'x8' x 6mm Marine Ply (for dome panels)
€ 83.73 for 4 x sheets 4'x8' x 6mm Marine Ply (for telescope tube)
€110.72 for 3 x sheets 4'x8' x 12mm Marine Ply (for dome ribs)
€110.72 for 3 x sheets 4'x8' x 12mm Marine Ply (for telescope tube)
€115.20 for 8 x 4.8m lengths of 6"x2" floor joists
€207.36 for 18 x 4.8m lengths of 4"x2" studs
€470.40 for 56 x 4.8m lengths of 5" T&G planking (floor + walls)
€ 40.00 for 8 x 600mmx600mm concrete paving slabs (foundation load spreaders)
€174.24 for 150m or 1"NG polythene tube for underground cable duct.
€14.31 for 2 rolls of orange builder's twine for cable duct pull-thru.
€39.95 for 5 litres of waterproof wood glue.
€257.95 for 22 sheets of 4'x8' x 4mm WBP Ply (cladding for inside of the dome)
€39.95 for another 5 litres of waterproof wood glue - gotta stop sniffing this shit!
€272.90 for another 13 6"x2" floor joists, 30 joist hangers and nails. I forgot about these!
€46.21 for nuts, bolts and screws.
€9.68 for 16 300mm galvanised steel straps to hold the perimeter joists together.
€67.20 for 4 more 6" x 2" x 4.8m joists.
€70.62 for 10 litres of Protim wood preservative, brushes and floor brads
€19.44 for floor brads (for nailing the walls and floor.)
€19.40 for a roll of heavy duty builder's plastic for lining the walls and under floor.
€16.95 for welding rods - for the telescope tube assemblies.
€5.97 for 40 M4 x 20 machine screws for mirror cells.
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€3085.16 + blood, sweat, tears, labour and bananas for the bloody Orangutans!
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Control Hardware & Software:
€89.78 TheSky 6 (Serious Astronomer's Edition) Software Bisque ($129.00)
€56.00 Vellman USB Interface Kit
€00.00 Relays for dome motors
€30.00 Lesve Dome Driver Software

And so to work...