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Re: [ATM] truss poles; was: How Big is Too Big?
My design for an OTA is simpler. I have wood for the
mirror cell and metal all the way around. It's 3/4"
aluminum angle and 1" aluminum flat stock. The
focuser is held in place with a piece of 1x6, on the
inside of the frame. The mount points are on the
inside of the frame, and the DEC bearings are the
front axles of tenspeeds. I'm working on a
brake-drive system for the RA and DEC axles; ball
bearings are slippery.
I'm going to cover this open framework with cloth.
The inside is black fake velvet and the outside is a
star chart pattern. This will block out excessive
light and slow the air down around the aluminum frame
members.
Kevin
--- Dave Smith <smithersscope@yahoo.com> wrote:
> Hi Jay,
> Just a couple of comments:
>
> >You still have to follow the basics and make sure
> that
> > the bearings aren't flexible,
>
> YEP!
>
> > A mild caution: the trilateral design
> > is not the easiest to build. Instead of just two
> > bearings that need to be absolutely square
> > with and centered upon each other, now you have
> > three (altho the rear
> > bearing does not necessarily have to be centered
> on
> > the same CoG,
> > depending on how you want the scope to elevate).
> You
> > need to be extra
> > careful in design and construction. Added to that
> is
> > trying to ensure
> > that the altitude bearings to line up over top of
> > the azimuth bearings,
> > more critical than in a traditional dob. It took
> me
> > two tries to build
> > my flex rocker properly. So go into it either with
> > everything drawn up
> > on paper, not forgetting to configure both
> > horizontally and a little
> > past the vertical beforehand and/or be ready to
> > consider your first
> > build a prototype. On the plus side, outweighing
> > every other concern,
> > it's a brilliant design.
>
> Couldn't agree more! Draw it up first! Even then,
> that
> 3rd dimension can come back and bite you in the
> pants.
> Beware of optical clearance if you mount truss
> connectors directly to the alt. bearings, too!
>
> >But how do I transport 9' truss tubes? Now I have
> to
> > experiment with 2 part truss tubes.
>
> I found extendable 1" aluminum tubes at Home Despot
> (painter's poles). 10 feet when fully extended, $12
> USD each (that's cheap aluminum tubing and it's
> already anodized!). Each pole has two segments
> connected by one threaded friction joint (a big, but
> lightweight knurled plastic knob). I've learned that
> I
> can collimate by adjusting the truss pole length
> instead of the the three collimating screws on the
> secondary. No threat of screwdrivers doing
> half-gainers onto my primary! Of course this will
> mean
> re-collimating every time I set up if I collapse the
> trusses. They collapse down to 5 feet or less. The
> joint is VERY stiff when snugged down by hand.
>
> NOW, if I could just get one of the woodworking
> gurus
> on the list to teach me how to tap wood threads into
> truss clamp blocks, I could screw the truss tubes
> directly into the truss blocks using the preexisting
> aluminum threaded ends on my poles.
>
> HTH,
> Dave
>
>
>
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