[ATM] truss poles; was: How Big is Too Big?

[Dave Smith <smithersscope@yahoo.com>]

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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