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Jon
Isaacs
Postmaster
Reged: 06/16/04
Posts: 6462
Loc: San Diego, California
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Race to First Light: Lightbridge vs Dobstuff |
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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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