Original+TRO+Telescope

Above is a picture of Geoff Regan and Dave Owen with the recently completed 30 inch (TROK) at Lynn-Brenig, North Wales,UK on Suday morning May 3rd 1998. (Dave Thomson is taking the photograph).

The 30 inch dobsonian telescope shown was designed and built by Dave __**T**__homson, Geoff __**R**__egan, David __**O**__wen and Steve **__K__**ing (also named after its team members, Dave Thomson, Geoff Regan, Dave Owen and Steve King). It has taken us fouteen months of spare time work (mostly on Saturdays and Wednesday evenings) to complete both the optics, tube assembly and mounting.

The 30 inch mirror was ground and figured by ourselves and is made of 1 inch thick plate glass. The glass was bought from a local firm in St Helens as a 30 inch nipped edge blank and then hogged out to the approximate curve in my garage using a 22 foot long scaffold pole acting as a radius arm. One end had an adjustable ball joint fixed at the wall at one end of the garage. A 6 inch carborundum wheel, bearing assembly and black and decker drill was at the business end with a constant water slurry running over the wheel for lubrication.

It took 6 months of Saturdays to hog out the mirror to a depth of 10.5mm in the middle. This gave us 3/4 of a bucket of ground out glass! Tool wear was counteracted by adjustment of the ball joint at the other end of the radius arm. Two 6 inch wheels where used to hog out the mirror. The curve was measured to be accurate to 1/4mm over the entire surface which was deemed acceptable before going on to the next stage.

The rest of the grinding and figuring was done mirror face up ontop of an old oil drum in my garage. We used a sub-diameter tool to take out irregularities from hogging out. This was done by fixing 4 layers of 3/4 inch plywood together, covering the surface with car body filler and then pressing into the upturned mirror. This gave the approximate curve of the mirror for the tool. It was then covered in epoxy glue and 2 inch metal washers were arranged on the surface. 60 to 320 grade carborundum was used to even out the surface prior to fine grinding with 500 aluminium oxide. The mirror was polished with a similar tool but being slightly larger and covered with optical grade pitch. A fast acting slurry of cerium oxide and water was used to bring the mirror to a polish. Figuring was done with a smaller 8 inch glass tool covered in pitch. This was done by progressively deepening the centre to the required parabolic curve. Focult, ronchi and zonal tests where used extensively to keep a check on the figure. Figuring proved to be a difficult but possible. Plate glass can respond dramatically to temperature and enough time has to be left between work sessions and testing to allow the mirror to stabilise.

The reason for building such a large telescope was inspired by reading about the spectacular views you get through these instruments. The popular American magazine Sky and Telescope show these large instruments being used in star parties in the States. The costs of buying such an instrument are prohibitive so the amateur telescope maker has to turn hand to whatever he can lay his hands on. The total cost of the telescope was £700, cheaper than some commercial equatorial mounted 8 inch telescopes. It is not extremely difficult to make a mirror but it is time consuming. Literature from library books and the Internent where used and help and advice from many people have helped to get us this far. If you are keen then give it a go, we did, this is the first mirror we have ever made.

In May 1999 both Myself (Dave Thomson), Geoff Regan and Dave Owen were given and award from the LAS (Liverpool Astronomical Society) for the Advancement of Astronomy for the design and build of the TRO telescope. Below is us after recieving the award.



Dave Owens notes on making the original TRO

Original TRO Introduction and concept Original TRO Purchasing the blank and hoging out Original TRO Testing the curve for accuracy Original TRO Making the tools for grinding by hand Original TRO Evening out the irregularities left by rough grinding Original TRO Polishing and testing Original TRO Making the mount and tube assembly Original TRO Making the secondary flat Original TRO Aluminising the primary mirror Original TRO First light

CREDITS
This project would not have been posible without the help, however large or small, from those listed below and others yet to be mentioned. Many thanks to them all. **//A special thanks must go to our long suffering families for being patient, supportive and also in helping out during construction (i.e. plenty of cups of tea and cakes!).//** Specialised Glass (For the glass blank being cut so well) Steve King (Helping in many ways all the way through, Structural work, grinding, polishing etc) Phil Leighton (For Ideas and help in figuring) Andrew Bates (For ideas and help) Peter Drew (For ideas, encouragement and glass for the secondary) Yvonne West (For making the light tight sock to go over the tube) Phil Harman (structural work) Steve Southern (Pictures and helping with grinding work) The Gerard Brothers (For Ideas in mirror making) T.E Hughes (nuts bolts, tools etc.) Layton fasteners (Nuts Bolts etc.) Craven Engineering (For the focus mount) B&Q (Taking time out to cut the Tube and mounting). Orion Optics (for advice and grinding materials)

Image below shows the TRO at my house in 2002 with the 16 inch F6 Dobsonian.



Image below shows the TRO at Croxteth Hall in 1999 at it's first star party. We had quite long queues behind it all night!