Last updated: 24 February 2006
Subject: Of Home Made Star Diagonal's... Sent: Sunday, February 19, 2006 07:11:17 From: martin dawson (email@example.com) Please find attachments for making a home made star diagonal. Please feel free to chop and change to your taste. It was made with a view to be used on a Meade LXD-55 AR-5 5-inch refractor but I guess it could be used on any refractor that could take two-inch eyepieces. Hope it contributes something to the some total of human knoweldge!!! Regards and Best Wishes, Martin Dawson The York Astronomical Society, England, UK. A Home Made Star-Diagonal by Martin Dawson YAS It started as not so much an 'argument' but more like a 'heated discussion'. After a York Astronomical Society meeting we all convened into a local pub, then it started, one of the lads (John Roberts) said "I'm going to buy a Star-diagonal" and I blurted out "Well, I'm going to make one!" and that was my mistake, so of we went! Another friend said that we could make a short video film, so the seed's of an idea were planted. I used to work for Vickers Instruments, an optical company that used to be based in York and one of there products were tank sights (see box). There were always substandard parts lying around and if you asked the appropriate shop foreman nicely he would let you have some. One item I had had for a few years was a nice 45deg prism some 45mm wide and 70mm on the long side. Not big enough for a 2" SD but certainly up to the job for handling 1.25" EP. I joined a local school's engineering course (again...) to use there facility's. First of all I made a wooden pattern, as I was not sure of the shape I wanted I just made a simple wooden block and from that casted a billet. I could have bought a block of aluminium but that is not as much fun! I found some waste casting's from a factory that made a high quality product, what I don't know, they looked like filter housings, what ever they were a well made product, it didn't matter as they where soon in the crucible melting away. The wooden block was surrounded by casting sand and soon created a void. When the aluminium was molten, in it went! After half-an-hour or so it was broken out and was soon in a lathe (four jaw chuck) having a hole drilled through it. Next I bored open the hole to 33mm diameter and copied the profile of the adapter for my AR-5, next it was to the milling machine to machine out first the inside then when I was happy it would take my prism I machined the out side surface's and mating surfaces. Next I made two lids, one would have a 33mm diameter hole in the center and apart from the hole both lids would be identical. The corners where swept out to half the thickness of the plates and drilled. The lids were then offered to the box to mark out the position of the holes that were next drilled in to the box. When this was done they were tapped to M4 and the lids fastened. Next job was the longest and most tedious, fettling, using various files and progressively finer emery paper I cleaned up the outside surfaces. I also paid particular attention to the corners. To hold the prism, I first drilled six holes - three per side - and tapped to M5. Position was determined by the shape and size of the prism. Two brass plates were next with a thin sheet of rubber stuck to one side. Using grub screws, the screws worked against the brass plates with the rubber - and two sheets of black card - bearing against the prism sides. Final machining task was the turning of a brass Eye Piece holder, with a flange at one end and four mounting holes, and two thumb screws. One small job was the stamping of a mark, in Ref a, I came across a excellent article on the punch marking of early scientific instruments. Engraving was a lengthy and highly skilled process whereas punch marking could be undertaken relatively quicker. Also individual marks on instruments where akin to silver marks on jewelry and this appealed to me. Vickers Instruments had a large inspection department and large components that had passed quality control where stamped in a inconspicuous place, I had 'acquired' a metal stamp with "VIY3" - Vickers Instruments York inspector no. 3 - using this seemed to show a link with the old firm and with the instrument makers of old. When I was happy that everything fitted the two lids and the box were powder coated. Finally, I had a badge from Vickers Instruments which I fixed to one of the sides. The stylized "V" for 'Vickers' and the "I", in the shape of a eyepiece for 'Instruments'. The screws were M4 slotted cheese head's from? Yes, you guessed, Vickers Instruments as well as the thumb screws! Although it has one or two 'Quality' issues, I'm happy with it, after all it is a working item. Once while browsing through a Meade catalogue I found some Flip-Mirror systems that had square bodies and further more the Star-Diagonal on Meade's DS-60EC is 'square' and looked a little bit like my Star-Diagonal, this suggested to me a little bit of commonality... Footnote. Vickers Instruments Ltd, York was an optical company that was based in York, England from 1964 to 1988. They were part of a much larger concern that built aircraft (VC10's), submarines, Tanks (Chieftain, Challenger 2) and a whole range of other products. Vickers in 1916 took over two old established firms, Troughton and Simms of Rochester and T.Cooke and Sons of York. T.Cook and Sons were formed in the late 1840's and built a lot of very fine astronomical instruments. Barr and Stroud, an old optical company based in Glasgow made sights for Chieftain tanks was absorbed into the Pilkington Brothers concern in 1977 (a & b). Some of there products were made by Vickers Instruments in the late 1970's early 1980's (b & c) References (a) Bulletin of the Scientific Instrument Society, No.73, June 2002. (b) War Monthly, Issue 40, July 1977. (c) British Army Equipment Exhibition Programme, 23-27 June, 1980. I worked in the glass shop and fitting shop between 1975-80 and 1990-92. Thanks go to the following for the assistance in this project, Mr. Martin Whipp for producing a video diary and supplying aluminium. Mr. John Roberts for starting the ball rolling. Mr. John Ashwell of Fulford School, York for the use of the school's equipment and supplies. Mr. Andy Lawson for helping with sourcing a powder coating service. Mr. Gordon Peacock for supplying some excellent magazines that provided inspiration. and finally, the unknown Lens and Prism maker's who made the prism some years ago...
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