Re: ATM Truss Tubes - Flare Fittings are superb!

[Paul Shankland <pshankland@flakeysol.com>]

Hi all,

"Bertapelle, Ken" wrote:

> Kurt, Paul, et. al.,
> [clip]
> Imagine holding a tube in your hand using the two different styles of
> attachment.  There is much more bearing surface in the second case than
> in the first, and this is why it seems to me that the second is more
> rigid.  Don't get me wrong, however.  I'm not saying that using inserts
> wouldn't work.  And other considerations, such as compactness might make
> it more attractive.  But still, IMO rigidity of the OTA is the primary
> consideration, and so if it were me, I'd use the clamping blocks.
>
> - KenB

[clip]
and...
        From:
               Mel Bartels

> [clip]
> In a truss tube, all that matters is that there is a single unmoving
> point of support at each end.  The threaded connectors fulfill this
> requirement nicely.  From this point of view, the Obsession style
> connectors are over designed,[clip] It might also be argued that
> the truss tube clamps hold down vibrations transmitted through the truss
> tubes, but a properly designed telescope can have truss tube vibrations
> that never appear at the eyepiece.
>

Hi all -
Gotta agree entirely with the general logic on the clamp block designs - which
is why I started with clamps (basically for every reason Mel stated). Indeed,
the clamps are 'over-constrained', kinda like a 4-legged 'tripod'... They
capture the poles for the upper cage installation nicely.  It just turned out,
for me, the Flare fittings had the edge. I found they are much more 'compact',
they won't split like clamp blocks (I read about such nightmares, late at nite
etc etc...) - unless you buy metal 'blocks', they are wear-resistant, the
fittings are relatively cheap, easy to find locally, and yes, the flares do
kind of 'capture' the poles for installation. My male fittings are angled for
truss alignment, and as I put my poles on, even horizontally, they are VERY
close to their attachment points for the upper cage. The poles go on well in
the dark, and once the poles are 'close' to hand-cinched, they allow very easy
upper-cage attachment, with enough 'give'. AND, once tight, they have every
bit the holding power of a block (unless you are building a cast-iron upper
cage... THEN the block-typess are at risk of splitting due to torsional
stresses). Envision that the threads of the fitting are pulling the flare hard
against the male fitting. Just like the clamp block, when tight, the assembly
acts as 1 unit - just like a trailer receiver pin handles the load of a
monsterous trailer. To imagine holding the tip a pole vs putting a hand around
it is erroneous, cuz your hand/fingers are flexible & do not act as 1 unit. If
rigidity worked that way, towing boats & trailers would entail monsterous
rigs... In fact, the flare fitting is safer - threads are less likely to
loosen/back off  than the clamp blocks losing friction (but hey, ya got 8
poles as backup!). They have the safety of being threaded. That itself is a
minor setback to the flares - ya gotta spin 'em on & off - blocks were quicker
(but not much). Bottom line is, they are both quite strong, as 1 unit, both
guide/align for the upper cage well, one is a tad faster, one (my greatest
need) is a tad more 'trim' and compact. And I thought they metted out Occam's
razor better, in their simplicity. I didn't need overconstraint. And I tested
both, I just like the net plusses of the Flare fittings from experience.

My assessment, however misguided... <grin>
best, Paul