The Ochra South Observatory

Visit The Ochra South Observatory here.

If the Keck Observatory can sport a double moniker (Keck North and Keck South) then so can The Ochra Observatory!

Ok, so both of my observatories are just a wee bit smaller than either of the Keck jobs, and in the case of my Southern data gathering facility... smaller than a finder scope! But hay, In your face Keck!!!

Visit The Ochra South Observatory here.

Stud Wall Outer Cladding

December 2008: With all eight stud wall frames done it was time to nail on the outer cladding. To help keep out the damp, I first stapled on a sheet of heavy gauge builders plastic on the outside of the stud wall frames. This was then covered with the outer cladding - 3/4" tongue and groove floor planking that had first been liberally painted in brown Protim wood preservative - I defy any woodworm to try dining on my observatory!! The plastic sheet was deliberately cut too large to allow for wrap-around on the top and sides, and to allow a skirt to hang down outside the floor joists.

Above: Moisture membrane on stud wall

Above: Partially clad wall with window.

Of the eight walls, the three north, north-east and north-west walls will be solid, while the west, south-west, south-east and east walls will all have windows, and the door will be in the south facing wall.

Above: South stud wall with main entrance.

The next step is to knock up a door and four windows and shutters and add a little decorative detail to take the garden shed look off it!

Stud Wall Pre-Assembly

Back to work! After a couple of weeks doing other work around the place, I decided to buy a decent table saw to cut and shape the stud wall end studs... I wish I had bought this thing earlier, as it has made life soooo much easier in general!

Anyway, I reduced my small mountain of raw lumber into lots of smaller pieces and set about cutting out the rebates in the lintle and foot-plates of the stud walls. The end studs on each of the eight walls must be cut to a trapezoidal shape to make everything fit snugly:


So, after a bit of fun with the glue pot and a large hammer, I knocked out 8 stud wall sections, which I was delighted to find all fit together perfectly. With each pair of walls aligned and G-clamped together, I drilled through the studs in three places and bolted them securely together. And here's the result!


It really is quite roomy inside - and I haven't even put on the roof yet!!

Next job is to drown every squate inch in builder's grade Protim to preserve and protect the wood - a smelly, messy job!

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!