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Parallelogram mount rebuild & q's on finishing

ATM Binoculars Mount
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#1 Zamboni

Zamboni

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Posted 16 April 2021 - 11:24 AM

Last year I was given the EXTREMELY generous gift of a homemade parallelogram binocular mount on an old CGEM tripod along with a pair of Zhumell 25x100 binoculars (not to mention a killer observing chair for use with my dobs). Over a year of use I came to one inescapable conclusion; it was impractically large for the way I was using it. The guy who built it (fellow CN'er Project Galileo) is a ridiculously tall individual, and built it to accommodate use by even more freakishly tall individuals. As such the boom is over 3 and a half feet long between pivot points.

 

After much deliberation (and getting a new zero gravity chair to use with the binoculars, prompting a desire for easier setup) I decided to retrofit it for maximum manageability, safety, and stability. This would involve new boom beams and a new counterweight shaft. The results are pretty great, and now all I have to do is finish the wood which is a step I have a few questions on. I'll get to that at the end.

 

First photo below is the "before" photo. It's built from red oak. The boom has a significant moment arm. The counterweight bar is a 3/4" diameter steel tube with holes drilled through it. It uses 1/4-20 bolt knobs that mount to threaded inserts in the wooden boom to secure the shaft. The counterweights are old Celestron weights.

 

I had concerns about this counterweight setup's long-term durability. There was a distinct possibility of the pole failing from the counterweight load, as well as that much weight riding on a pair of quarter inch bolts. There's also nothing to act as a toe saver on the end of the shaft, so the only thing holding the weights on is the friction of the weights' adjustment pins. I was also worried about blundering into the weights in the dark, and the end of the shaft could put an eye out. I decided in the revised version to replace the shaft with a threaded rod which would hold the weights in place with large hex nuts.

 

Before starting, I measured the mount in relation to the Zero-Gravity chair I was intending to use with it.  I wanted to determine the BARE MINIMUM length the boom needed to be to give the binoculars and chair adequate clearance around the tripod and also be able to properly position the binoculars above the chair when the tripod legs are fully retracted. This puts the binos a little too low at their highest position for viewing while standing up, so for outreach I'll extend the tripod legs. Because of the positioning of the finder at the front end of the binoculars I can still easily look through the finder while standing with the legs retracted.

 

The lower beam is 20" long with pivot holes 18" apart. The upper beam is 24" long and uses bent copper conduit straps to create a channel to slide the counterweight shaft into. The shaft is then secured at either end of the beam with hex nuts. This also gives me a greater flexibility for positioning the counterweight shaft so that none of it is sticking out past the hex nut that secures the rear end of the counterweight. The forward end of the shaft doesn't present a poking hazard because of the mount head, and the shaft doesn't stick forward far enough to interfere with the mount head.

Since I was already doing a full teardown/rebuild of the mount, I took the opportunity to refine and fine-tune the azimuth bearing, the altitude bearing on the mount head, and the swing hinge. Motions are smooth and deliberate with no wobble.

 

So overall the mount is now VASTLY lighter, safer to operate, easier to set up, and much more stable. All that remains is finishing the oak of the new beams.

 

I'm not super concerned about completely matching the appearance of the existing wood. If anything, I think having a bit of a mismatch gives it a punk DIY ship-of-theseus vibe that appeals to my chaotic-neutral nature, and I'm going to be using it in the dark anyway. My main concern is cheaply and easily finishing it to protect it from moisture. Emphasis on as easy as possible. I've already sanded the wood to 220 grit. If there's any one-stage finishing options I'd like to hear them. I'm not an experienced woodworker by any means and I'm a firm believer in form following function and the K.I.S.S. principle.

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#2 Zamboni

Zamboni

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Posted 05 May 2021 - 03:43 PM

Wound up going with a Minwax Polyshades "classic oak" 2-in-1 stain/poly. Also augmented the counterweight bar attachments with big honkin' washers. I'm very happy with the results. The mount has been reassembled and I'll be testing it out in depth finally tonight.

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Edited by Zamboni, 05 May 2021 - 04:03 PM.

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