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Re: [ATM] 16in tridob rebuild 1st light (ball sockets)
Hi Anthony,
I thought it was an original idea while trying to
solve the issue/dilemma of the complicated angles in
the tri-dob. Then I stumbled onto the moonlite focuser
webpage. Definitely not original! (Acck!)
I purchased the wooden spheres from Michael's--the
art/craft chain store (doll heads?!). I used the 2inch
version; I think I could probably get away with a
smaller diameter. I used thin ca to reinforce the
threads in the tapped wood blocks. I've only had to
rethread one block so far for slippage; used JB
Weld...no more issues!
Dave
--- Anthony Anconetani
<Anthony.Anconetani@genband.com> wrote:
> Hi Dave,
>
> I like the ball and socket joints for the truss
> work. Where did you find
> the wooden spheres?
>
> -Anthony, Round Rock TX
>
> > -----Original Message-----
> > From: atm-bounces@atmlist.net
> > [mailto:atm-bounces@atmlist.net] On Behalf Of Dave
> Smith
> > Sent: Wednesday, August 22, 2007 5:51 PM
> > To: ATMLIST
> > Subject: [ATM] 16in tridob rebuild 1st light
> (long)
> >
> > Just wanted to quickly report the results on the
> rebuild of
> > my trilateral dob.
> > I've had the beast out in the driveway the past
> three nights
> > tweaking and adjusting. The orange streetlight
> glow in my
> > 'hood is borderline unacceptable, but then options
> are
> > limited when you need your tools handy.
> > :O) I'm in Orange County, southern California; I
> suppose it
> > could be worse, but the temperature IS perfect and
> there's
> > little wind.
> >
> > Jupiter was excellent at moments with detail
> sufficient to
> > see both major spots and adjacent swirling
> patterns. Seeing
> > was hit or miss and it took some patience and
> averted vision
> > to see the detail.
> > Moved on to several of the clusters in Scorpio and
>
> > Sagitarius. Glow nearer the horizon was
> troublesome, but the
> > images were very crisp as long as we didn't push
> > magnification. (16" f5.6, 3.1 inch secondary,
> using different
> > combos of 2 inch EPs: 52mm and 48mm Rini's and a
> 19mm SWA
> > Russel Optics with my 2x Pocono Mntn Barlow). M13
> and M57
> > were also excellent at near zenith; definitely
> more contrast
> > with the thinner atmosphere/smog layer. M57 was
> ghostly blue
> > with some fine detail visible even at low power.
> VERY rewarding.
> >
> > Now, commenting on mechanical performance...
> > In the rebuild I enlarged the ground ring diameter
> from 28 to
> > 35 inches and the alt bearing diameter from 20 to
> 30 inches.
> > This was done to allow for a larger mirror box, a
> more stable
> > stance of the OTA in the flex rocker and higher
> center of OTA
> > rotation. The full weight of the scope places
> formica bearing
> > surfaces directly on SS rollerblade bearings.
> > Definitely suboptimal. In the short 3 nights under
> the stars
> > I have divits and grooves in two of the 4 bearing
> surfaces
> > (the ground ring and the main altitude centerfin).
> They
> > affect pointing even at low power and the original
> fantastic
> > smoothness is gone.
> > Sigh. I've also discovered that the flex rocker
> flexes in one
> > dimension too many. Where my bearings are mounted
> at about 45
> > degree angles on the top surface of the flex
> rocker I see
> > that the wood is buckling outward allowing the
> altitude
> > surfaces to contact the flex rocker. Nice
> unintentional
> > mechanical brake! I tried to quick-fix by
> reinforcing the
> > joints of the rocker, however it only reduced the
> rub instead
> > of eliminating it. Not sure how I'm going to fix
> that. I can
> > "carve" away the area that rubs in the flex
> rocker, but I
> > suspect the rocker will just stretch to accomodate
> more of the OTA.
> > I'm still having problems being nose heavy. I've
> reduced the
> > top of the OTA to a single ring, a red dot finder,
> a 2"
> > homemade crayford and the most simplistic truss
> clamps (a
> > small piece of aluminum angle, a 1/4-20 carriage
> bolt and a
> > hand nut). The spider mimics Mel's wire version.
> My secondary
> > mirror is approx 1" thick. I used ball/socket
> joints to
> > capture the trusses at the mirror box and endring.
> They work
> > extremely well. Complicated trilateral angles are
> no more. I
> > swapped them out at the end ring though--too
> heavy. Even
> > eliminating this weight, she's still nose heavy.
> I've slapped
> > the extra 25 pounds of lead (from tridob version
> 1.0) on the
> > center fin level with the ground ring. It's well
> balanced
> > with the lead. No spring virtual counter weights
> at this
> > point, but I'm planning on trading lead for
> springs very soon.
> > My truss tubes were adjustable painter's poles.
> Over time and
> > use hand tightening of the joints caused a couple
> of the
> > plastic joints to crack and fail. So, due to the
> slippage and
> > undesireable concommitant decollimation, I cut the
> threaded
> > plastic unions off and JB-Welded the two joints of
> aluminum
> > tubing together (both are ~1" dia/thin walled).
> The OTA is
> > now rock solid and stable.
> > I have two fans installed in the mirrorbox and
> aimed across
> > the surface of the primary. They work well as
> before.
> > My ground ring and centerfin already have the JB
> Weld/putty
> > epoxy threads in place and I've built up the
> stepper motor
> > assemblies--they're good to go, I think.
> >
> > All in all, I'm very pleased with the rebuild. The
> floppiness
> > of the original OTA is GONE. I need to solve the
> flex rocker
> > issue and line the bearing surfaces with steel.
> That should
> > solve my "issues".
> >
> > And THEN it's time to motorize.
> > I'll be updating the website soon. It's partially
> updated
> > now, but no final images.
> >
> > the SolidWorks digital version:
> >
>
http://dsmith.no-ip.org/smithersscope/atm/solidworks.htm
> >
> > and the page of images of the rebuild:
> >
>
http://dsmith.no-ip.org/smithersscope/atm/Tri-Dob%20Reconstruction.htm
> >
> > As always, I couldn't have done it without y'all's
> help!
> > Great group! Cool hobby!
> > Clear Skies!
> > Dave
> >
> >
> >
> >
> >
> >
>
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> >
>
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> >
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