Treebolts revisited

[Allegheny Tom]

So I ran some quick ballpark numbers to try and rationalize why the CF bolts seem to be split between guys who break them and guys who are confident in them.

The bending moment at the base of the bolt is your weight (plus any bouncing load) * the exposed length 3 5/8 in
The polar moment of inertia of a 3/8 in cylinder/circle is pi/4*(3/16)^4 = 0.001 in^4
The cross sectional area is around .1in^2

The flexure formula for bending force gives bending force Fb=M*r/I, for the case of a tip load, supported as either a perfect cantilever from the tree, or supported at 2 points (the deepest part of hole, and the outside of the hole)

For a 200 pound person/load at the tip that is 140 KSI.

The rockwest carbon has a compressive strength of 270 ksi. so load it roughly double on a bounce, and it gets into "failure" territory.

Grade 8 bolts have a rated tensile strength of 150ksi and yield strength of 130ksi and proof load of 120ksi - but we don't hear much about people bending their grade 8 bolts? In principle you should be able to bend them by standing on the ends, with maybe a slight bounce. Why is that? Is it because the rating on bolts is NOT a material rating, but a fastener rating (and there is less material, more stress concentrations, etc. in the threaded area of the bolt when used as such...so the actual material in the unthreaded portion is a bit stronger)? Or is it because the carbon is so darn rigid (but wouldn't the tree likely give more anyway?)

Or do people bend their bolts, not break them, and just shrug it off because the failure mode is much more benign?

https://gwcomposites.com/carbon-rods/ (and https://www.tapplastics.com/uploads/pdf/Pultruded_Carbon_Rods__Tubes.pdf )
These guys list shear strength for a sililar product that's a lot lower (as expected for unidirectional carbon) - a spec that rockwest doesn't guve - but still for an area of 6 KSI, so say a 600 pound breaking load, or still a bigger safety factor than the bending load (on the bright side it seems like tip loading is potentially only 50% worse than just standing on them...)

Disclaimer - I haven't really done much of any solid mechanics calculations in probably 15 years.

Say what? Can you phrase that in terms than even an ex brewery worker can understand?
What's the bottom line? Carbon is better than we give it credit for and grade 8 is not as good as we think???
I love my grade 8 bolts. I'd really like carbon. I'm probably 185 or 190 with gear. Im betting carbon would be fine, but as said earlier, it only takes 1 break.

 

[mattsteg]

Say what? Can you phrase that in terms than even an ex brewery worker can understand?
What's the bottom line? Carbon is better than we give it credit for and grade 8 is not as good as we think???
I love my grade 8 bolts. I'd really like carbon. I'm probably 185 or 190 with gear. Im betting carbon would be fine, but as said earlier, it only takes 1 break.

Short version:
the carbon's strength spec appears to be higher, but clearly they occasionally break. That might be due to e.g. the lack of flexibility/bounce, vulnerability to nicks/damage, or some other factor I haven't thought of.

We don't hear about grade 8 bolts failing, even though the "spec" (which does not cover bending accurately - actual bending strength away from the threads could be ~50% higher) for them is lower.

Shorter version: Like you - I want to believe, but without a cause "this is why they broke"...I just can't. If I'm at the limit, I'd rather be at the limit with something that will bend a bit as warning. And if I'm that close on safety margin, I want to know where and what the limit is - not just "be careful".

 

[kyler1945]

So I ran some quick ballpark numbers to try and rationalize why the CF bolts seem to be split between guys who break them and guys who are confident in them.

The bending moment at the base of the bolt is your weight (plus any bouncing load) * the exposed length 3 5/8 in
The polar moment of inertia of a 3/8 in cylinder/circle is pi/4*(3/16)^4 = 0.001 in^4
The cross sectional area is around .1in^2

The flexure formula for bending force gives bending force Fb=M*r/I, for the case of a tip load, supported as either a perfect cantilever from the tree, or supported at 2 points (the deepest part of hole, and the outside of the hole)

For a 200 pound person/load at the tip that is 140 KSI.

The rockwest carbon has a compressive strength of 270 ksi. so load it roughly double on a bounce, and it gets into "failure" territory.

Grade 8 bolts have a rated tensile strength of 150ksi and yield strength of 130ksi and proof load of 120ksi - but we don't hear much about people bending their grade 8 bolts? In principle you should be able to bend them by standing on the ends, with maybe a slight bounce. Why is that? Is it because the rating on bolts is NOT a material rating, but a fastener rating (and there is less material, more stress concentrations, etc. in the threaded area of the bolt when used as such...so the actual material in the unthreaded portion is a bit stronger)? Or is it because the carbon is so darn rigid (but wouldn't the tree likely give more anyway?)

Or do people bend their bolts, not break them, and just shrug it off because the failure mode is much more benign?

https://gwcomposites.com/carbon-rods/ (and https://www.tapplastics.com/uploads/pdf/Pultruded_Carbon_Rods__Tubes.pdf )
These guys list shear strength for a sililar product that's a lot lower (as expected for unidirectional carbon) - a spec that rockwest doesn't guve - but still for an area of 6 KSI, so say a 600 pound breaking load, or still a bigger safety factor than the bending load (on the bright side it seems like tip loading is potentially only 50% worse than just standing on them...)

Disclaimer - I haven't really done much of any solid mechanics calculations in probably 15 years.

I had an ME at work run these calculations. If you’re interested in reviewing the work, shoot me a PM to discuss. In a nutshell with the pointload in the center of the rod sticking out the tree, the safety factor is probably enough to make most folks under 200lbs comfortable if they are careful thoughtful climbers. Above 200 gets less so. Standing on the end of the rods changes everything dramatically....

It left me with making the recommendation that if you’re over 200lbs, you’re walking a thin line, and I wouldn’t recommend it. If you’re under, I’d only recommend to people paying attention, and experienced in climbing/using proper fall prevention.

I’m 190lbs and I feel fine using them.

 

[Vtbow]

For anyone over 200# (and this isnt necessarily a sale plug, but kinda ) I had found some NOS treehopper cordless drill bits in 1/2" a while back and was going to experiment with them for a possible ROS of CF rods, or upgrading my setup, but I feel super comfortable with mine still and too many projects and too little time. I bet the 1/2" cf rods are significantly stronger without adding much weight at all. I have three of the bits and threw them in the classifieds. They could easily be drilled and converted for a hand drill too.

 

[PJC]

For anyone over 200# (and this isnt necessarily a sale plug, but kinda ) I had found some NOS treehopper cordless drill bits in 1/2" a while back and was going to experiment with them for a possible ROS of CF rods, or upgrading my setup, but I feel super comfortable with mine still and too many projects and too little time. I bet the 1/2" cf rods are significantly stronger without adding much weight at all. I have three of the bits and threw them in the classifieds. They could easily be drilled and converted for a hand drill too.

Pm sent.


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[Nutterbuster]

I was waiting on @kyler1945 to chime in on this one.

I think that carbon bolts fall in the same category as cutting leg straps, replacing waist buckles with non-load bearing alternatives, not backing up a ropeman, and hanging from t-screws. I wouldn't blindly recommend for the masses to do any of those things. But plenty of folks have done the math, weighed the odds, and decided they're comfortable with it.

It's weird to climb on something that weighs less than a sharpie marker. I love them, but consider them a calculated risk.

 

[Vtbow]

I was waiting on @kyler1945 to chime in on this one.

I think that carbon bolts fall in the same category as cutting leg straps, replacing waist buckles with non-load bearing alternatives, not backing up a ropeman, and hanging from t-screws. I wouldn't blindly recommend for the masses to do any of those things. But plenty of folks have done the math, weighed the odds, and decided they're comfortable with it.

It's weird to climb on something that weighs less than a sharpie marker. I love them, but consider them a calculated risk.

I was waiting for @kyler1945 as well. I agree 100% with @Nutterbuster and Kyler's comments.

 

[kyler1945]

I was waiting on @kyler1945 to chime in on this one.

I think that carbon bolts fall in the same category as cutting leg straps, replacing waist buckles with non-load bearing alternatives, not backing up a ropeman, and hanging from t-screws. I wouldn't blindly recommend for the masses to do any of those things. But plenty of folks have done the math, weighed the odds, and decided they're comfortable with it.

It's weird to climb on something that weighs less than a sharpie marker. I love them, but consider them a calculated risk.

I think it would be a good idea to evaluate your entire climbing setup and process if you're interested in using something like this, but are thinking "IS IT SAFE, JUST TELL ME!!!". The answer is not black and white - as mentioned above.

Humans suck at intuiting statistics - what that means is when someone tells you the odds of something happening to you, the result of that is often negative. First - there's no telling if they used their ****ty intuition to arrive at those odds, and second, you're very likely to misinterpret that information, and get yourself into a situation with mismanaged expectations.

The best we can do is to incorporate some math, think pragmatically about the whole situation, and make calculated decisions with careful thought and deliberation. Since most folks won't do the best they can do, and want that work done for them so they can feel warm and cozy, I'd recommend avoiding the cutting edge of lightweight hunting gear. This was my beef with the original predator platform when it came out. It was my opinion that the folks involved did not take into consideration that thoughtless, careless people would get their hands on it, and face significantly worse odds of a failure than was implied. I think the redesign incorporated some more beef to address that, and I'm grateful for it.

I would imagine that in your evaluation of your entire process of hunting/climbing, you'll uncover some areas where you expose yourself to significant risk of injury or death. And by significant I mean relative to what you think (casually of course) might happen to you. When you do this, and factor in the math on the bolts, things will become a bit clearer.

You see - if I say "yeh you should definitely use them, there's plenty of safety factor"- that's wildly irresponsible. I'm not taking into consideration any of the detail about YOU and your situation. That's YOUR responsibility.

I think my formal response from now on will be "if you have to have a yes or no answer, my answer is no, don't use it"

EDIT - However, if you'd like to PM me and discuss the math we've done, and how it might relate to you, I'm happy to discuss!

 

[Vtbow]

I think as I have mentioned many times before, my personal thought is risk managment is 100% individual. Are you backed up if somethign goes wrong? Are comfortable at heights to begin with? do you have a ton of experience climbing rock or trees and are comfortable taking 30' whippers on 1/4" square piece of steel with a welded cable loop in it threaded into a small crack in a piece of schist that's hundreds of years old and you can't calculate it's solidarity? risk managment is based upon YOUR experience and comfort levels and needs to be made by the individual putting themselves in the situation.

That being said,somethings are just stupid and dangerous and should never be done I'm sure everyone will chime in if it's on that end of the spectrum!

 

[Nutterbuster]

Yep, risk calculation is an individual thing. A 20-something year old arborist with a girlfriend is a different man than a 50-something year old with a wife and kids and a bad back. Different abilities, and different responsibilities. Where and how you hunt figures in. How over built the rest of your gear is or isn't.

It's comparatively easy to run numbers on material specs and compare that to industry standards. But to me that's just a starting point.

 

[Vtbow]

Yep, risk calculation is an individual thing. A 20-something year old arborist with a girlfriend is a different man than a 50-something year old with a wife and kids and a bad back. Different abilities, and different responsibilities. Where and how you hunt figures in. How over built the rest of your gear is or isn't.

It's comparatively easy to run numbers on material specs and compare that to industry standards. But to me that's just a starting point.

And we have to remember "Industry standards" in the saddle world is really quite loose at this point in time.

 

[Ontariofarmer]

I feel safe using them up to 8 feet. All our climbing is a risk. So is driving the car especially when we have a blizzard.

That said, I can see why people worry about recommendations on safety . There are too many lawyers in the world and too many dumb mistakes.

My mistake was being 200 pounds plus gear plus a soft pine tree with an elongated hole and uneven pressure on the carbon fiber peg. Never happens right. I guess in my invincible 20's I would go for it. I only weighed 175 pounds then too and was not in my sixties.
I think that CF bolts are fairly safe but.... from at least two breakage experiences by two different individuals in similar situations we can learn why they broke which is good for users and non users.

 

[EricS]

Reminds me of my first carbon fiber fishing rods. If you were hung up you could pull all you wanted on the handle and it wouldn’t break. If you grabbed the rod closer to the tip it took very little pressure to break them. At 290lbs I have yet to bend a grade 8 bolt.

 

[mattsteg]

I had an ME at work run these calculations. If you’re interested in reviewing the work, shoot me a PM to discuss. In a nutshell with the pointload in the center of the rod sticking out the tree, the safety factor is probably enough to make most folks under 200lbs comfortable if they are careful thoughtful climbers. Above 200 gets less so. Standing on the end of the rods changes everything dramatically....

It left me with making the recommendation that if you’re over 200lbs, you’re walking a thin line, and I wouldn’t recommend it. If you’re under, I’d only recommend to people paying attention, and experienced in climbing/using proper fall prevention.

I’m 190lbs and I feel fine using them.

I'd be interested in seeing the work...as you say tip-loading makes a significant difference. Even then my calculations (and I'm horrendously out of practice) say tread lightly, keep your knees bent, and wear flexible-soled boots.

 

[GodsCountry]

Cool thread here.

I’ve turned my nose up to bolts in the past, but lugging around sticks in the brush has got me reconsidering.

What’s the consensus on coating the bolts? Are coated bolts a no brainer? Is plastidip a one and done, or does it come off? I see treehopper sells coated bolts, I’m just not sure it’s worth the price vs DIY. Anyone have trouble seeing the black bolts at night? Has anyone experimented with bright colors?

 

[PJC]

Cool thread here.

I’ve turned my nose up to bolts in the past, but lugging around sticks in the brush has got me reconsidering.

What’s the consensus on coating the bolts? Are coated bolts a no brainer? Is plastidip a one and done, or does it come off? I see treehopper sells coated bolts, I’m just not sure it’s worth the price vs DIY. Anyone have trouble seeing the black bolts at night? Has anyone experimented with bright colors?

Plasti dip is a no brained and is durable. Red is almost as hard to see in the dark as black but with a head lamp jumps out at you. Either are easy to see with a head lamp. Red is easier to see in gray light but it’s also easier for other hunters to see.


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[PJC]

There are some down sides to bolts of course. No method is perfect. I ran I to one on Saturday morning as I got to the tree I was planning to hunt and the holes were all full of ice. I had to drill them all out. It took alias much effort as drilling them from scratch. Almost. I made the mistake of not getting out of all my cold weather gear and I was a sweaty mess when I got to hunting height.


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[Chrighton]

I've had holes ice up before

 

[PJC]

I've had holes ice up before

It’s a pain.


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[Allegheny Tom]

Cool thread here.

I’ve turned my nose up to bolts in the past, but lugging around sticks in the brush has got me reconsidering.

What’s the consensus on coating the bolts? Are coated bolts a no brainer? Is plastidip a one and done, or does it come off? I see treehopper sells coated bolts, I’m just not sure it’s worth the price vs DIY. Anyone have trouble seeing the black bolts at night? Has anyone experimented with bright colors?

I've found heat shrink tube to be more durable than plastic dip, and heat shrink is instant. No need to dip them, hang them and wait for them to dry. Cut shrink tube to the proper length (don't coat the part that will be in the tree) and put heat to it...It's done, it's neat, and it's ready to use instantly.
Not all shrink tube is created equal, though. I got this off Amazon. I chose the 1/2" stuff so it would cover the bolt heads of a 3/8" bolt. It won't completely shrink around the top of the bolt head, but it will make bolts quieter in your pack if the sides of the head have shrink tube on it. One small issue is you will have to grind the hex of the heads to fit the 1/2" tube on. Takes me less than 30 seconds to grind the head. There can still be a head remaining if you want to have that profile on your bolts. I wanted a little bit of head remaining. I got the red stuff. Definitely easier to see climbing down, but also more noticeable to other hunters if you leave them in the tree. It's a trade off.
XHF2018 Dual Wall Heat Shrink Tubing 3:1 Ratio Heat Activated Adhesive Glue Lined Marine Shrink Tube Wire Sleeving Wrap Protector Red 4Ft (12.7mm (1/2"))