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DISPLAYING POSTS TAGGED: great melbourne telescope (2)

Great Melbourne Telescope volunteers

Author
by Kate C
Publish date
13 March 2014
Comments
Comments (1)

Each Wednesday, a dozen or so engineering and astronomy buffs head to a museum workshop to restore one of Marvellous Melbourne's grandest marvels. The Great Melbourne Telescope (GMT), scorched by the Mount Stromlo fires in 2003, is being resurrected thanks to an estimated 10,000 hours of volunteer work (so far). This group recently received a Certificate of Appreciation in the 2013 Arts Portfolio Leadership Awards.

GMT restoration team Mathew Churchward reading out the Arts Portfolio Award commendation to the Wednesday restoration workshop team.
Source: Museum Victoria
 

The workdays have "a bit of a men's shed feel about them," says Senior Curator Matthew Churchward. He coordinates the project alongside Curator of Engineering Matilda Vaughan. The combined knowledge in the room – all members of the Astronomical Society of Victoria, many with experience in engineering, electronics, astronomy and optics – means this piece of 19th-century technology is in expert hands.

Three men with computer L-R: Barry Cleland, John Cavedon, new volunteer Norm and Stephen Bentley working on technical drawings of GMT parts.
Source: Museum Victoria

Building telescopes is a common pastime for amateur astronomers; volunteer Barry Adcock has a home-built a 14-inch diameter telescope for his backyard dome observatory, plus another telescope that allows him to view the stars from inside his house. For many, stargazing is a habit they picked up when very young. Scottish-born Jim Pollock recalls a lunar eclipse in 1949 during which the moon was bright blue after forest fires in Canada. "In the atmosphere, tiny particles of pinene, the oil from the pine trees, scattered red light beautifully and just let the blue light through." Another volunteer, Barry Clelland, remembers looking up as a kid from his backyard in the suburbs and thinking, "that's half the universe there. You could see the Milky Way in Heidelberg back then."

On this day, a sub-group is working on the mirror polishing and grinding machine, a beautiful hulking contraption with a cast iron frame and gears and shafts. The GMT's half-ton speculum metal mirrors tarnished over time, so every few years they were removed and reconditioned with this machine. "We're still trying to work out exactly how it was driven," says Matthew. The mirror sits on a rotating table and as it moves, the polishing head also rotates, "so it doesn't get a flat spot in any part of the mirror. It keeps moving as it's rubbing." Or, like "patting your head and rubbing your tummy," jokes volunteer David Linke. The team hopes to have the polishing machine working within the next year as a hint of what's to come with the telescope itself.

David Linke with the mirror polishing machine. David Linke with the mirror polishing machine.
Source: Musuem Victoria
 

In the workshop, parts of GMT are laid out on pallets and benches. With a grin, David says, "it's a big jigsaw puzzle, isn't it?" Above it all, for equal parts reference and reverence, hangs a large-scale historical picture of the GMT in operation.

Museum workshop A view of the workshop with the GMT’s lattice tube in the foreground. On the back wall hangs the large historical photograph of the GMT at the Melbourne Observatory.
Source: Museum Victoria
 

Most of the large parts of the GMT were recovered after the 2003 Mt Stromlo fires. "Oh golly, it was a dirty job to get everything out of that cube," recounts David. "The aluminium had melted from the dome and filled up the screw holes so you couldn't see where things were undone." Many months of work saw the GMT dismantled and its surviving parts audited. Fortunately, the GMT had an unofficial champion in Barry Clark, who has been involved with the Melbourne Observatory since 1955. At that time, decommissioned equipment went into storage and was at risk of being lost. Says Matthew, "Barry's been instrumental in recovering bits and pieces that were hidden under the floor. He's discovered some key bits of equipment that went right back to the very earliest observatory at Williamstown."

Detail of the dismantled cube of the GMT. Detail of the dismantled cube of the GMT.
Source: Museum Victoria
 

Lengthy reverse-engineering is recreating the missing parts. "We go out there with a ruler and pencil and paper, take measurements and sketch it up roughly," says Campbell Johns. The measurements are made in imperial units to match Irish manufacturer Thomas Grubb's original specifications, before conversion to metric for fabrication. Some of the team with technical drawing expertise convert the workshop sketches into digital CAD files. There's a lot of cross-checking with old photographs, drawings and the extant parts.

"We don't even know if there was ever a full set of working drawings," says Matthew. "It appears they did the basic layout and started building it before they had the detailed design. You can see evidence in the way parts were modified during the construction process, like spots flattened out of a casting to make a seat for another component." A volunteer adds, "Pretty amazing given in those days there were no angle grinders or power drills or oxy welders. It was all done with cold chisels."

Three men with computers L-R: Barry Clark, Barry Adcock and Mal Poulton working on optics design specifications for the GMT.
Source: Museum Victoria

So why are these men devoting their spare time to this project? It's evident from the way they talk about the GMT that they admire its history and innovation. In addition to its astronomical achievements, including the first observations of southern nebulae, the ingenious nature of its design bewitches them. It had two axes and counterweights that allowed just one person to move the beautifully balanced telescope. In its lifetime there were larger scopes, but none so nimble. Matthew's view is that it's an opportunity of a lifetime for amateur enthusiasts to build such a large telescope; few individuals would have the resources to do so alone. Other volunteers nominate restoring an important part of Melbourne's history as their prime incentive – they want to see it back in its old home.

Indeed, the end goal is to return the working telescope to the Melbourne Observatory for public viewings. Its original configuration restored, there may be new electronic additions to allow digital photography or remote operation via the web. As Matthew says "It could be very inspiring for astronomy in Victoria."

Links:

The Great Melbourne Telescope website contains the story of the telescope, and updates about its restoration through the ASV's Phoenix newsletter

Follow the GMT project on twitter: @GMT21stC

Great Melbourne Telescope on Collections Online

Casting for the Great Melbourne Telescope

Author
by Matilda Vaughan
Publish date
21 December 2012
Comments
Comments (1)

Matilda swapped a life working as an engineer for a life curating the museum’s historical Engineering collection. She’s very curious about how stuff works, how it’s made and why. If a machine’s got a switch, she’ll definitely flick it.

Last week I visited a foundry in Melbourne that was casting a vital component for our restoration of the Great Melbourne Telescope. The original part of the telescope - the declination disc - had been modified and broken at some time in its history and was not repairable.

Great Melbourne Telescope in 1870 The Great Melbourne Telescope in its own house at the Melbourne Observatory, 1870. The red arrow points to the declination disc needing replacement.
Source: Museum Victoria
 

This is the first part of the project to be made by a sand moulding or casting process very similar to that which was used in Ireland in the late 1860s. Our modern part is made from a type of cast iron invented in the 1940s which has magnesium added to give it properties that make it easier to shape. The electric induction furnace, which is used to melt the metal, was developed in the early 20th century.

A couple of weeks ago, Peter made a pattern out of wood for the casting. Tom next used the pattern to form a hollow in a sand mould. This kind of mould is a mixture of washed sand and a binder, made in two halves, and cured to retain its shape once the pattern is removed. The two halves of the mould were then closed, after a pouring spout, flow paths and risers (to allow the metal to flow to and fill all sections of the hollow) were added. Heavy weights on top ensured it remained closed when the metal was poured.

Man working with metal The sparks fly as Bryn takes a sample from the furnace for temperature testing.
Image: Matilda Vaughan
Source: Museum Victoria
 

The pounded earth floor and the filtered light through the open doorways and skylights in the roof of the foundry transported me back in time. It was 7 AM and Bryn had already been awake for hours and the sparking pot of molten metal (spheroidal graphite iron) was his morning's labour. He tested its temperature and composition, turned the knob of the electric induction furnace's control panel, and gave the signal. After the removal of the slag crust, the metal was ready for pouring.

Man pouring molten metal Bryn pours the molten metal into the next mould as Tom looks on. Our filled mould is on the floor behind them.
Image: Matilda Vaughan
Source: Museum Victoria
 

Bryn added the final ingredients and carefully tipped the 1500°C molten metal into the pre-heated ladle. He then transported the ladle to the moulding area and poured it first into our waiting mould, and then onto the other smaller moulds. Being such a large casting, ours needed almost 24 hours to cool down before breaking open the mould.

Sand mould in workshop The lower half of the sand mould, with the casting removed. The sand from the top half is in pieces in the background. The sand will be cleaned and reused, as will the molten scraps of metal.
Image: Matilda Vaughan
Source: Museum Victoria
 

At 6 AM the following morning, Bryn was ready to break open the mould. The weights were removed and the upper part of the mould lifted away. Then the casting itself was lifted into the air and the sand and metal debris removed. It was then transported by the overhead mobile crane to the finishing room, where the hardened parts of the spout, risers and flow paths were ground and knocked off and the surfaces cleaned.

Men with newly cast metal pieces Bryn (left) with the pattern for our declination disc, and Tom (right) with the freshly removed casting. Note the four cylindrical 'risers' at the edge, the pouring pathways (almost like a running person) in the middle and the square shaped pouring spout (head of the running person). These pieces are reused for the next batch of metal.
Image: Matilda Vaughan
Source: Museum Victoria
 

The next step for this part will be heat treatment to 'relax' the metal, followed by the final shaping and machining. It is a rare sight to see this process so close in our urban environment and one of the great aspects to working on restoration projects of this magnitude.

Links:

Great Melbourne Telescope website

Great Melbourne Telescope on Collections Online

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