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Jon Isaacs
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Reged: 06/16/04
Posts: 6462
Loc: San Diego, California

 

jon16Inch

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The Race to First Light: Lightbridge vs Dobstuff  

A secret race to First Light... my Dobstuff conversion vs the 16 inch Lightbridge.

The short story: I will let you decide, I think we won by a hair in a photo finish, last night was First Light for my Dobstuff conversion of a Meade Starfinder, a dim view of Venus through the clouds.

The long story:

In January I ordered a kit from http://www.dobstuff.com/ to convert my 16 inch Meade Starfinder DOB into a Strut Style scope. When I got the Starfinder (Craigslist)last fall it was immediately apparent that the 100lbs+ OTA and 75lb base were back-breakers and that I would have to design and build something that was lighter and more transportable. Being a mechanical engineer, designs raced through my mind like candy but of course nothing actually happened outside the fantasy world.

In January I saw an ad on Astromart from Dennis Steele advertising that he would make the wood parts for a DOB and when I looked at his design, it looked to be much like what I had been fantazing and so after some discussions, I ordered the parts. They arrived less than three weeks later and while there was minor issue with the tube connectors, everything looked beautiful....

In fact the parts looked so beautiful that drilling a hole or touching touching them in any way was just too scary. So I went back into the fantasy mode and considered all my options, how exactly was I going to put this thing together?

Being a rather poor wood worker, I was not quite sure how to proceed. I finally got the courage and ordered the tubes for the struts and in a stroke of genius, I went to see a cabinet maker at work. After discussing my various options (none attractive as they required skill) the talk turned to music and playing music and I discovered he was a rather talented on the sax and clarinet. He gave me a CD of some of his work with the band "Tobacco Road" and I went home, gave it a listen and it was pretty good... Then I hit track 6, a fantastic version of "Ain't Misbehavin'" and for past two weeks that one song has powered the assembly of the scope. I figure I heard that song just about 500 times...

Assemblywise, being a mechanical engineer, I went with what I knew, aluminum angle corner pieces with 1/4-20 bolts and tapped holes. With my $59 drill press and a Chinese band saw I cut and fit each piece. First drilling the aluminum angle, clamping it place to drill pilot holes in the wood, disassembling it to drill the wood and tap the aluminum. A tedious process but one that is very strong and can be disassembled and guaranties everything fits.

It took one Saturday to assemble the base and when it was done, well I was a happy camper. It looked very nice, was very solid and yet less than half the weight of the Starfinder monster base. I could lift it with one hand.

I frazzled my brain over choosing the length for the tubes, basted it over the focuser position and fried it worrying about the balance but finally I had machinist friend cut the tubes and the assembly of the OTA began. The first night in a couple of hours the basic OTA was assembled, a three ring design and I was WOWED by the lightness and stiffness. I had done some caculations and decided that 2 inch OD tubes with a 0.050 wall would be light and very stiff...

A few nights later, I installed the mirror and its old cell and the scope was beginning to take shape. It was looking good.

Yesterday was the final push. Fueled again by Tobacco Road's "Ain't Misbehavin'", I began at 8am. All that was needed was a bracket for the focuser, brackets to attach the secondary spider to upper ring, to attach the Ebony star to the altitude bearings and to attach the altitude bearings and braces to the lower mirror lower assembly.

Eventually I will build a nicer focuser mount but I wanted something simple to make that I could just clamp in place so I could experiment and find the ideal position. It all would have been a lot easier if the focuser had required a 3.0 inch hole instead of a 3.1 inch hole but 3 hours later I was done with the focuser and a trip to Home Depot and I was back with the right bolts to finish job.

It was at just that moment that the switch on my trusty band saw gave way but with a hour detour and a trip to Radio Shack, I was again up and running. Fabricating and installing the brackets bearing braces and for the spider took much of the afternoon. I took the time to print out a full sized CAD drawing of the ring assembly to get the placement of the parts...

The final step was installing the altitude bearings and the braces. This went smoothly and by 8pm, the final strains of the clarinet and piano were filling the night air and I WAS DONE...

Venus was barely visable through the clouds but I went for it and sure enough, I was able to reach focus, the balance was on the money and I was ready for some tacos....

So... Did we win??? Did this slow starting jockey pull it out at the last moment, racing to make the final assemblies as the 16 inch LightBridges were on the trucks heading to happy new owners?

I will let you decide who won but I will say this: This scope is a winner. The OTA will come in about 55 lbs with everything. The base is solid yet light, 30 lbs or less. This scope has the action of well made truss DOB with the full sized (18 inch diameter) altitude bearings and of course that wood is nice to look at.

There is still more to be done. I need to apply a finish to all the wood, make a shroud and decide on exactly where I want the focuser. There maybe other issues that come up, all solveable. Clearly someone with half an idea of how to work with wood could have finished this in less than a day but the time was well spent and the finished scope has it's own personality.

Given my total investment, I think this scope is quite remarkable. The original scope was $350 used, the focuser $70, the wood parts from Dobstuff were $499 plus shipping, the tubes and the aluminum angle were $100 and I used about $50 worth of nuts and bolts.

I also have to say that Dennis Steele is a pleasure to work with. He was willing to build anything I wanted but in the end, I went with his designs because I knew experience is more important than fantasy. When I had a question, Dennis was there with a photo and explanation to guide me.

Best to all, Clear Skies Ahead...

Jon Isaacs

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