Would you trust a $1,000 on this joint ?

[Roy Hess]

I really could use some opinions about the application of a “bed bolt”type fastening system in my application.


What you are looking at is called a Binocular Mount. They are used to hold large binoculars for astronomy enthusiasts. These binoculars can easily reach 25 X 100 power and beyond, 18” long and weigh up to 14 pounds. Because of their shear size, mounting them in some way to a tripod has many advantages.


I have changed my design somewhat, and am now proposing a 90 degree connection, using 1 3/4” Oak, a 3/4” piece of maple doweling, and a 3” x 5/16” stainless lag screw. All of this is assembled the same way that you would a bed bolt, for bed rails, or even a woodworking bench. I have made a slight modification, by adding a shallow dado in the vertical piece (1/4” deep ) for additional support.


Everything that I have read about these joints is that they are very strong. Considering that this specific joint would be holding at max, say, 15 pounds, with some minimal side to side pressure when in use.


So picture yourself using such a rig set up on a concrete sidewalk, with 15 pounds of glass hanging out there...................

[Brian Effinger]

What is the other end of this attached to (where the light colored arms are)? It seems to me that there would be a lot of tourqe? on the joint in question.

[Bruce Page]

Roy, that's a pretty good sized lever arm hanging out there. If it were me, I'd make at least the horizontal piece out of aluminum.

[Roy Hess]

What is the other end of this attached to (where the light colored arms are)? It seems to me that there would be a lot of torque? on the joint in question.Brian - Here is a picture of the unit setup. Notice the change in location where the binocular holder connects with the parallelogram.

[Mark Mack]

Couldn't you just attach the binocular mount to the vertical piece of the parallelogram?

[Tim Sgrazzutti]

If it were me, and I wanted to stick with wood, my choice would be a bridle joint.

[Bill Petersen]

I voted yes, but then....they're not my binocs. I think that joint would have the strength. I'd be more worried about knocking the whole darned thing over.
Bill

[Brian Effinger]

Couldn't you just attach the binocular mount to the vertical piece of the parallelogram?
Or get a taller tripod?

Anyway, I'll stick with my poll respose of adding some sort of bracket. I just wouldn't trust such an expensive set up to only the bolt. A back up would be nice.

[Don Bullock]

I didn't vote because my choice isn't there. Bill made a good point that I agree with.


I'd be more worried about knocking the whole darned thing over.

If it were me I'd do something totally different that was a lot more stable. I think your binoculars extend too far beyond the center of the tripod. It just doesn't look like it's well balanced.

[Paul Steiner]

I would be more worried about getting caught looking in your neighborlady's window.

[David Moody]

Roy,
Have you checked in with this at the DIY ATM forum on Cloudynights.com? There are several folks there who have made bino mounts and would probably have some excellent experienced based advice to give here. I would check there just because of the experience base with this type of construction.

I have worked on building dobs, but not bino mounts. However, my experience with most of them is that they use aluminum and/or steel brackets with vertical pins to hold the binocular underswing mount to the parallelogram. You have a pretty dynamic load out at the end of that moment arm, so I agree with your concern.

[Fred Belknap]

probably work but I wouldn't trust it. a simple half lap with a bolt or two would be more secure.

[Roy Hess]

Couldn't you just attach the binocular mount to the vertical piece of the parallelogram? Yes you could, but you would begin to limit the full range of motions, and the versatility of the parallelogram.


If it were me, and I wanted to stick with wood, my choice would be a bridle joint. That's an interesting option. I may give that a try - Thanks !


If it were me I'd do something totally different that was a lot more stable. I think your binoculars extend too far beyond the center of the tripod. It just doesn't look like it's well balanced.Yes, you might think so. The surveyor type tripods give good stability when in use, and the long reach of the parallelogram is considered an advantage when sitting down and viewing from a chair.


Have you checked in with this at the DIY ATM forum on Cloudynights.com?Yes, I post there regularly. Thought that I would post this question here as I am interested in comments from the woodworking community, on the strength of the wood joint, as opposed to the design of the mount.

Thanks for your comments so far, they really are helpful !

[John Schreiber]

By any normal measure, that should be strong enough. It's just imagining $1,000 worth of glass hanging off of it that scares me.

One - you could reinforce it with some aluminum plates screwed into the wood from each side. That should make it bomb proof, but you would have to come up with something clever to make it removable.

Two - mount something twice as heavy as your binocs on there and try to break it. When it doesn't break, you will feel comfortable with your usual load.

Three - add a safety wire, so that if it breaks, it just bonks you in the face and doesn't hit the pavement.

[Steve Rozmiarek]

Wonder if you could just make the horizontal piece different, rather then just one square profiled piece, make it more of a triangle tapering down from where the parrallegram ends, to the mount for the binocs needs to be. That way you would have room for two bed bolts, rather than just one, which should more than double the strength I'd think. Keep the shallow dado though.

It would at least address the major problem of the bed bolt pulling the grain out the end of the horizontal member, and immediantly dropping your pricey glass. Two would probably provide you some notice if they where to fail.

You could also skip the bed bolts, and just mill the whole part out of one piece of lumber, and take your chances with the bolt on the binocular end.

I think you're fine as is, but...

BTW, I've always thought that those binocs where more expensive then that, could they be used to focus on much closer objects, like several miles?

[willie sobat]

I concur with others who have recommended a half-lap (possibly reenforced). I used a similar design (dowel and lag-screw) to reenforce the dry M&T joints that hold the headboard in a bed I built. I used that arrangement, not for strength, but to allow the joint to be tightened periodically.

[Tom Clark FL]

Hi Roy,

I understand the idea of your type of mount.

However, being a minimalist, I kept with a simple Dob type bino mount. It weighs 2 pounds, uses no counterweights, and has been solidly, safely holding my 20x80s for around 18 years. There is no worry of joint failure, and absolutely no vibration either.

There are many solutions to every problem, right?

[Lee Schierer]

I wouldn't trust it for several reasons. First lag screws are not that strong and are likely to eother snap of or strip out of the cross dowel. Make the cross dowel out of metal and use a standard threaded bolt. A grade 5 bolt would be strong enough.

Second there are stronger joint methods already mentioned. Your 15 pound binoculars are at least 12" away from the joint. That lever arm is exerting more than 240 pounds of pull on your bolt and the small section of wood between the dowel and the vertical member. Would you hang yourself from that more than 3 feet off the ground?

My vote would be to design a different wood arrangement, which is not an option in your poll.

[JohnT Fitzgerald]

Roy, that's a pretty good sized lever arm hanging out there. If it were me, I'd make at least the horizontal piece out of aluminum.


I second that.

[Mitchell Andrus]

Any force applied to the rig will knock it over or wreck the binocs before the joint breaks. The weakest link in the assembly is NOT the joint you're worried about.

[David Keller NC]

There's absolutely no way you're going to shear that bolt off. I'm an engineer, so I have to know obscure stuff like bolt shear strength, and I can tell you that it will take way more than 1000 lbs. to shear it in two. If it concerns you, get a "grade 8" bolt, which are far stronger than a mild steel bolt and nut (though more brittle in constant vibration applications).

However, as a telescope owner/user, I can tell you that you've a bigger problem with the design. The bracket that's holding the binoc mount is going to be prone to vibration, and that really sucks in a telescope mount. Even the slightest hand pressure will allow the image to wiggle around, and since you don't have a clock drive on the device to follow the celestial movement, you have to have your hand on it almost continuously.

Best way to evaluate this is just to take it outside tonight, focus on a star near the celestial equator, and observe it for 10 minutes. I think you're going to find the vibration very irritating.

[Lee Schierer]

There's absolutely no way you're going to shear that bolt off. I'm an engineer, so I have to know obscure stuff like bolt shear strength, and I can tell you that it will take way more than 1000 lbs. to shear it in two. If it concerns you, get a "grade 8" bolt, which are far stronger than a mild steel bolt and nut (though more brittle in constant vibration applications). I think the lag screw will fail in either by stripping out of the dowel or from tension due to the tightening torque and the mechanical load being placed on it by the weight of the binoculars. Common lag screws, even stainless ones are pretty low grade and break easily. The thread root at the base of the shank is the weak point. The thread creates a natural stress riser that initiates the failure. I've snapped off many 1/4" lags when tightening them by hand. I no longer use them on any item I build. I prefer to use the Timber Lok screws where I need to hold materials together.

[Peter Quadarella]

It looks fine to me. I use an aluminum parallelogram mount and they are awesome - chief among their advantages is the ability to sit in a lounge chair while viewing ;).

[Greg Funk]

If you're concerned about the joint, why not just build a test joint and add weight to the end of the lever until the joint fails. If it takes more than 4x the weight of the binoculars I'd feel comfortable using it.

[David Keller NC]

"I've snapped off many 1/4" lags when tightening them by hand."

I don't doubt that, it's very easily possible to break off bolt heads on any bolt given sufficient mechanical advantage, but that doesn't really mean the bolts are weak. Perhaps I've mis-understood, but in the OP's pictures, there doesn't appear to be any threads in wood - it's a bolt-through arrangement.

That said, you do have a point about running a bolt parallel with the grain in a bed-bolt type joint. He isn't gong to break it off, but he could indeed split the oak along the shaft of the bolt.

But that said, the problem isn't mechanical strength - it's vibration through the unsupported steel bracket and the possibility of tipping the whole rig over, with the multi-thousands of dollars binoculars impacting first.

[Scott Schwake]

I think it looks fine. You could add a band clamp around the arm & vertical piece for insurance. I like Steve's idea of making it out of one triangular piece.

[Maurice Ungaro]

Hi Roy,

I understand the idea of your type of mount.

However, being a minimalist, I kept with a simple Dob type bino mount. It weighs 2 pounds, uses no counterweights, and has been solidly, safely holding my 20x80s for around 18 years. There is no worry of joint failure, and absolutely no vibration either.

There are many solutions to every problem, right?

What Tom said.

[Roy Hess]

Thanks for the many replies, and great comments !!


One - you could reinforce it with some aluminum plates screwed into the wood from each side. That should make it bomb proof, but you would have to come up with something clever to make it removable.I have thought of this, in my poll it is what I meant by a "T brace"


BTW, I've always thought that those binocs where more expensive then that, could they be used to focus on much closer objects, like several miles?Like everything else in life, prices and quality, encompass a large range. My binoculars that you see in the picture were about $475 about 5 years ago. Today a good pair of Chinese made 20 X 80 can be had for $200. I have never tested for how close they focus, but I can focus at the end of my driveway - 50 feet.


That lever arm is exerting more than 240 pounds of pull on your bolt and the small section of wood between the dowel and the vertical member. Would you hang yourself from that more than 3 feet off the ground?Reading all of the comments so far, I agree that I need to set the dowel further away from vertical upright, and use a longer bolt. This wood leave more wood to take the stress of the weight. Am I understanding your comment correctly ?


There's absolutely no way you're going to shear that bolt off. I'm an engineer, so I have to know obscure stuff like bolt shear strength, and I can tell you that it will take way more than 1000 lbs. to shear it in two. If it concerns you, get a "grade 8" bolt, which are far stronger than a mild steel bolt and nutThanks for the comment - that sounds encouraging !


why not just build a test joint and add weight to the end of the lever until the joint fails.Actually, I was setting up to do just this very thing ! But I thought that I would post here first for some opinions.


I understand the idea of your type of mount. aaah - another lost soul !!

[Peter Quinn]

Would I trust a lag bolt's strength? Sure, they are very strong. I doubt a 14# anything is going to shear it. But pull out strength is another issue. And you will be exerting downward pressure that amounts to pull out force. I trust the bolt, its the wood I don't trust!:D Just keeps expanding and contracting and moving, looking all shifty, it will fail on you when you least expect it, maybe after years of faithful service.

I would be more inclined to skip that lag into long grain dowel arrangement (I have broken a few beds in my day) and use a threaded bolt into dowel nut set up like a counter top bolt or knock down hardware. Steel into steel, plug the holes and done. Now that I would trust $1000 on.