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Parallelogram mount question

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#1 Diego

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Posted 25 February 2004 - 02:02 PM

I will be making one of these pretty soon I hope. Been looking around the net for ideas. But one thing I don't get is, that some are advertised as being capable of keeping an object on target even if the binoculars are raised or lowered. I can understand "in the same direction", but not fixed on the object. Below is an example.

http://www.bigbinocu...com/stedivu.htm

Am I missing something :confused:

#2 Craig Simmons

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Posted 25 February 2004 - 02:36 PM

The p-mount allows the binos to stay pointed at the same angle regardless of how high the P-mount is raised and lowered. Only the booms change angle. The connecting pieces stay in the same vertical orientation. Since a star is so far away and huge, you won't see a difference in it's position. If you were looking at something 10 feet away, you would see higher and lower parts of the object as you raised or lowered the P-mount up and down due to it's closeness.

Craig Simmons
Falls Church, VA

#3 Diego

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Posted 25 February 2004 - 03:07 PM

Thanks Craig for clearing that up. Your explanation was what I first thought would really happen. With low mag and wide fields, the object will pretty much stay in the FOV. Now what would happen if you were viewing sitting on a chair, and then decided to stand up?

#4 EdZ

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Posted 25 February 2004 - 03:12 PM

The beauty of a pgram is that it keeps the object exactly centered No matter what the height from the max 7' to the min 3'.

If seated and you need to get up, swing the boom out of the way or push the pgram up. When you sit back down in the same position and swing the boom back or pull the pgram back down in front of your eyes, the object will be right there. Sitting in a slightly different position might throw you off slightly, but not much.

edz

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Posted 25 February 2004 - 05:30 PM

Diego,
If you are considering building your own p-mount then I would suggest using wood. I think Craig has put a plan here on this site for a p-mount he built from wood. I recommend the wood because it is more foregiving when cutting (metal is very unforegiving) and the wood seems to dampen vibrations quicker than metal.

I made my p-mount from 3/4-inch square aluminum tubing but I really needed 1" (had to be ordered and I didn't want to wait). The mount works O.K. but the extra 1/4-inch would have made it really rock solid.

The p-mount is definitely the way to go. Especially if you get a lawn recliner (perfect for looking at the zenith). "Good bye stiff neck!"

Good luck and Craig is probably the all time champion of home-made p-mounts.

Nick

#6 Rusty

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Posted 25 February 2004 - 09:21 PM

Nick, you might try foaming the inside of the aluminum tubing to both add strength and dampen vibrations.

#7 Diego

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Posted 26 February 2004 - 05:28 AM

Hello Guys, thanks for the responses.

Nick, wood was going to be my first choice. I thought about aluminum, but it was going to be more expensive and less stiff. Wood is much easier to work with as you say.
I'm a little concerned about the screws that hold the whole thing together, beeing that wood is softer than metal, is there any chance that the holes will get bigger with time? It will make the mount sloppy if this happens. Thought about using metal bushings on all joints, but this just makes thing more complicated.

Diego

#8 Craig Simmons

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Posted 26 February 2004 - 08:06 AM

Actually there is some metal in my P-mounts. I used Home Depot heavey duty shelf wall supports. However, I may be replacing these with oak to save weight and I've found that as thick as they are, the U-channel shaped shelf support still twists a bit due to the 2 foot length from the center support. There's room for another vertical connecting piece, so I'll try that first and see if it takes the flexing out.

One solution a fellow club member did with his aluminum P-mount was to epoxy copper tubing into the aluminum channel which strengthen the square aluminum tube without adding much weight. This was a rock solid mount.

As far as the overall tightness of the P-mount, you can tighten the bolts to the point where the mount is snug and moves but does not move freely like a seesaw. Lock nuts are good for this application. Weights would still be needed to keep the overall balance correct and to keep the mount from tipping over easily. If you want a free moving mount, you can use metal tubing with or without shims (aluminum roof flashing or equal) if the fit isn't exactly right. Oak is a pretty hard wood, and I don't think the bolts would wallow it out much if at all. If you make it a press fit with the bolts, it may be stiff at first but it will break in to a smoother feel as it gets used more.

Craig

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Posted 26 February 2004 - 09:12 AM

Rusty,
Great idea (foam inside of the square aluminum tubing). And I just happen to have a can of insulating foam spray that I was planning to use around a dryer duct that vents to the outside. Perfect, because I won't need the whole can for the duct! And I didn't cap off the ends of the tubing (I made the caps from wood but just have not inserted them yet ..... man, that was close).

Diego,
You will most likely use bolts and nuts versus screws on a wood p-mount so there shouldn't be a problem with the system becoming loose. Using washers will definitely help. I see that some commercial p-mounts use teflon washers for better tension at pivot points. I made some from 1/8-inch leather and they work great.

Craig,
I thought you had made a p-mount from oak. Perhaps it was from the Comet Couch article. Seems like I remember someone making a p-mount from oak, and it was a beautiful job. You did make an observing chair did you not? (Geez, loosing my mind at such a young age. :) )

All this talk about bino mounts has made me want to go out and observe tonight. The rain is suppose to stop today so it may be clean, dark skies tonight. It's Takies* Time!

Thanks all, Nick
*Takahashi 22x60

#10 Craig Simmons

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Posted 26 February 2004 - 09:55 AM

Here's the bino chair. Still a work in progress. Pic doesn't show latest changes to boom hardware.

http://www.cloudynig...rt=7&thecat=500

Here's the Tripod P-mount shown with 4 legs, currently has 3 and a different mounting arrangement for the binos (also not shown)

http://www.cloudynig...rt=7&thecat=500

Craig

#11 Diego

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Posted 26 February 2004 - 11:33 AM

[quote]
Diego,
You will most likely use bolts and nuts versus screws on a wood p-mount so there shouldn't be a problem with the system becoming loose. Using washers will definitely help. I see that some commercial p-mounts use teflon washers for better tension at pivot points. I made some from 1/8-inch leather and they work great.



Yeah, I meant to say bolts rather than screws, my bad. Maybe shoulder bolts and teflon bushings in the wood...

Diego

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Posted 26 February 2004 - 03:37 PM

The nice thing about making your own is that you can play with the mount until you get it exactly the way you want. As a matter of fact, I am working on my p-mount adapter at this very moment to move the Daisy red dot finder. Actually, I decided to add a brace and redo the outer surface in a heavy black felt.

The clouds are all gone and I thought I would be out peeking at the stars tonight, but the glue I'm using to apply the felt to the adapter may not be dry. Rather than rush it I'll just have to back off and let the glue dry properly.

Good luck with the project. Nick


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