The Fabrication of the Wyas Observatory - By Brian Joynes
The
dome ran as a separate project to the observatory and 18" reflector,
starting in early '82 and finishing in the summer of '83 just in time for the
inauguration of the observatory by Dr Patrick Moore that September. It started
late, perhaps because we were unconsciously avoiding it as we'd had our fill of
calamities in the building work of the observatory. No, on reflection, we were
consciously avoiding it! Finally, when we realised that we were going to have a
telescope but no roof to cover it with, we forced ourselves to discuss the
subject and asked for a project leader. Fortunately our oldest member Ralph
Emmerson, a retired cabinetmaker responded. He agreed to build it. My job was to
design it.
Silage
tower tops were much in fashion for observatories at that time, but as far as
Ralph was concerned that just wouldn't do. If we were going to have a dome it
had to be a "proper" one, just like the professionals. It had to have
the full hemispherical shape, rotate 360° easily and have a wide slot that
allowed access from horizon to beyond the zenith.
While
Ralph got on with finding a place where we could build it, I got on with the
design. What kind of slot, sideways opening or lift up, solid or roller blind
shutter, materials, how to make it rotate, rollers on the wall or the base ring.
Everyone I talked to was full of good opinions for every aspect of it, but as
expected, all different and few with practicality.
Ralph
coaxed a school in Normanton; a town 10 miles away, into letting us use one of
their wooden school buildings that housed 2 classrooms. They were
pre-fabricated, supposedly temporary classrooms, and used for woodwork, so we
had all the right tools at our disposal. We took the dividing wall and the
ceilings out to give enough space and height. We also had to level the floors by
getting under the building (it sat on 2' high brick built blocks), jacking them
up with car jacks and fitting packing pieces on top of the blocks. The dome team
of 4 met at the school every Monday evening for a couple of hours.
To
clear the telescope's movements and provide enough access to it, the dome had to
be 17' exterior diameter. Money was in very short supply just as with the
telescope and the observatory, so it had to be designed round available
facilities. These were Ralph's woodworking skills, his access to wood in various
forms from his generous previous employer and access to cheap aluminium sheeting
through another of our members. It followed therefore that the dome had to have
a wooden frame skinned with aluminium.
The
basic structure is a base ring with two hoops, main ribs, 3' apart arcing over
the middle portion. The space along the base ring either side is filled with 24
equi-spaced ribs arcing up vertically to contact the main ribs. The space
between the main ribs is filled with a 3' wide up-and-over shutter. All these
wooden members have an 8'6" outside radius. Though the base ring has flat
sections between the main ribs.
8'
x 4' sheets of half inch marine plywood, were sawn into 4' long x 4" wide
curved pieces, using an electric jig saw mounted on an 8'6" long radial arm
(Ralph's invention). 3 overlapping thicknesses of these pieces were laid, like
bricks in a wall, in a former on the classroom floor, screwed and glued
together, to make up each rib, 1-1/2" thick and 4" deep. Then cut to
their individual length and end angle, dependant on their position relative to
the main ribs. The glue was animal glue, boiled up and kept hot over a gas ring.
We used Cascamite for the final assembly on site.
The
base ring and the 2 main ribs were made similarly, but 6" deep. They were
built up on the same former as the ribs but screwed and glued into quarter rings
so we could get them out of the classroom. We nearly forgot that little detail
when we were deeply engrossed screwing and glueing the pieces together. The main
ribs are tied together behind the opening area, by straight "ribs" at
the top and half way down, to stiffen the whole structure.
The
base ring is not completely round, it has a flat length at both ends of the
shutter slot. This is so that when fully open, the rear end of the shutter can
descend below the level of the ring so the front end comes clear of the zenith.
Each rib is secured to the base ring with coach bolts and 2 off 4" lengths
of 3" x 3" steel angle. At the top we used blocks of wood. Lengths of
2" x 1" softwood were used at 2 levels, to stiffen the structure and
secure the ribs to each other. These spacers produced two rings of condensation
drips on the dome floor, and in winter when the inside of the dome was covered
in frost, the drips were very cold down your neck. We cured the condensation
problem by wallpapering the dome interior with 1/8" thick polystyrene
sheet.
Finally
all the various parts of the frame were completed and assembled in the
classroom, without glue of course, as a trial run, and we were very pleased with
ourselves to see the whole thing standing incongruously there in the room. It
looked huge, but would it fit? We painted all the pieces except where they were
to be glued, and numbered them carefully for re-assembly on site.
Click for larger image
While
the dome was being made in the classroom, the 2' high wall, that carries it, had
to be prepared on the roof. This was made of short lengths of 4" x 4"
softwood laid out in a 16' dia. ring on the roof and secured to the roof joists
through the used floorboards that formed the roof. Similar sized timbers were
fixed vertically to the ring and a 4" wide ring similar to the dome base
ring and made at the classrooms was fastened on top of them. More 4 x 4 timbers
were used to triangulate and stiffen the whole into a wall. Finally a 2"
wide x 3/8" thick flat rolled steel ring (we had to pay for this) was
secured on top to tie it all together.
Now
that the wall was firmly fixed to the roof we could finish the waterproofing of
the building. This was done one terribly cold and windy day in winter where the
only warm place was near the vat of molten tar. We laid 3 layers of roofing felt
90° to each other, across the roof and running up 6" all round the dome
wall. The inside of the dome area was not covered with roofing felt but was
given a 1" thick coating of tar mixed with an insulating material. This
added to the already well insulated (glass wool) ceiling, to ensure the warmth
of the meeting room below didn't get into the dome above. The wall was ready
during the winter, 6 months before the dome was, and the area inside the wall
was always filling with water, worrying us about leaks.
Fastened
to the outer edge of the wall are the 8 off 5" dia rollers that carry the
dome, mounted on their 8" sq. x 3/16" steel plates. Each plate allows
about 3/4" of vertical adjustment for its roller to ensure the dome is
level and all the rollers carry their fair share of the load. The
"rollers" are in fact double ball races in sleeves with a ring welded
on each end to give their outside diameter a deep "U" shape. After the
rollers were secured we could skin the wall with sheet aluminium, lapping over
the roofing felt and being careful not to cut through it. Later, the interior of
the wall was skinned with 1/8" plywood and red and white lights were
recessed into it.
On
the appointed day all the dome frame members and other ancillary parts were
brought to the site, together with welding equipment, glue and screws and lots
of enthusiasm. The 4 base ring pieces were placed, upside down, on a large level
"table" made of 6 plastic oil drums, and glued and screwed into a
complete base ring. The rolled 2" x 2" angle iron ring, made in 3
sections (we had to pay for this too), was then located on the base ring, still
upside down, and welded into a full circle. The steel and the wooden rings were
then drilled and bolted together making a very stiff base for the dome. When it
was turned over and lifted onto the dome wall, the angle iron track fitted
exactly into the "U" shape of the rollers, much to our surprise; and
in our relief we took a rest to ride round and round on it, testing of course.
The remainder of the dome skeleton took the rest of the afternoon to erect, and
a few more spins to test.
The
1/32" aluminium cladding took the next 2 weeks, 2500 steel screws and what
seemed like dozens of tubes of sealer, liberally applied between the sheet
overlaps. Having to use steel screws in the aluminium worried me but the
solution was to protect with epoxy paint. Fortunately one of our members was a
chemist at the local power station.
Under
the base ring we then fitted a long strip of 1/8" thick rubber to keep the
weather out of the rollers and dome. It keeps the rain out well enough but can't
keep the fine snow from blowing in. Though it could have been made to seal more
effectively it would have caused more of a problem with condensation.
1"
thick by 3" deep softwood cheeks were fitted to the inside faces of the
main ribs. On top of these for the full length of the main ribs we fitted
another pair of ribs 1-1/4" wide x 1-1/2" deep, again made of
softwood, screwed to the top of the main ribs. (On reflection, these should have
been hardwood, as they have to take all that the weather can throw at them
without much protection. They are beginning to rot now and will have to be
replaced in the next couple of years.) High tensile aluminium strips, 5mm thick
by 40mm wide, were then screwed along the full length of the top of these 2
ribs, overhanging inwards by 18mm, as tracks for the shutter.
The
shutter, made in the same former as the rest of the dome, is about a foot longer
than a full rib, so, when closed, the "front" sits on the base ring
and the "rear" is a foot over the zenith. When fully open the front is
a foot past the zenith and the rear is 2' below the base ring at the back, just
comfortably clear of the bottom of the wall.
Click for larger image
The
shutter carries 16 rollers in its two ribs, 8 each side, 4 load bearing (on top
of the strip) and 4 anti-lift (below the strip). The rollers are nylon and sit
on 3/8" dia. high tensile bolts, drilled through and fitted with grease
nipples. There is ample adjustment built in to take care of wear or settling,
but it hasn't been necessary to use it so far. The shutter is protected against
the weather by a 3/8" marine ply panel ending with a rubber strip either
side.
The shutter was originally opened by hand, by lifting the "front" from the inside till it is at the 45° position, where it feels weightless because it is evenly balanced on either side of the top of the dome. One then climbed out of the dome onto the roof and walks round to the back to pull it down the rest of the way. Though it required some effort and care, it wasn't excessive. I always intended to mechanise the process and have only just done so after 16 years of members' mutterings. On one occasion it was lifted with so much enthusiasm that it ran beyond the top, fell to the back and pulled screws out of the running strip. This helped to speed up the mechanisation.
The
structure is easy to rotate in either direction, though there are mutterings
about mechanising it. When closing down after an observing session we use 3
steel rods 3/8" thick to pin the base ring to the wall.
The
local town council, never having had to deal with anything as exotic as a dome
before, decreed that we clad it in copper sheet so that it would look well when
weathered to verdigris. Fortunately we were able to steer them away from that
enormous cost, but they insisted that if it couldn't be copper then we must
paint it a similarly dark green. We wanted it white to reflect the sun's heat,
so we compromised with a mix of green as light as we thought we could get away
with. It turned out a light apple green. We dubbed it Goose Green as the
Falklands war was raging at the time.
At
the inauguration in September of '83 all the dignitaries were impressed with the
observatory, telescope and dome, but Ralph was unable to take his due plaudits
having died just a fortnight before. It had been his dearest wish to meet
Patrick Moore.
The
dome gets its once a year maintenance work, as does the rest of the observatory,
but that is restricted to painting inside and occasionally outside.
By
Brian Joynes