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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Feb 19, 2017 - 04:42pm PT
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cool stuff, Moof, sounds like you are really dialling it in. And thanks for the tips on the CF to aluminium glue. My application is for a joiner which isn't in direct stress--I suspect I will have to go to glue, but right now I am experimenting with a rivet, but sandwiching the CF between two layers of aluminium so the rivet ends are not in direct contact with the CF.
Edit: the rivet solution seems to be working--not sure how much I have weakened the underlying carbon, but since the joint essentially is triple butted, seems ok. Not sure about breathing that carbon dust from drilling it though...
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BLUEBLOCR
Social climber
joshua tree
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Feb 19, 2017 - 07:41pm PT
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Moof, those look really nice. Good job!
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Moof
Big Wall climber
Orygun
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Feb 19, 2017 - 08:28pm PT
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Another learning that I made the hard way is to angle the center shark fin MUCH more than you think you need to. I did my first floor +/-4" from the center line, which was way too little. Your feed need so much less than your shoulders. 6-8" offset from centerline on each end is a good target.
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edavidso
Trad climber
Oakland, CA
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Feb 19, 2017 - 09:39pm PT
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John, your strength index seems like a good way to compare relative strengths of specific tubes as it describes the max moment each can take before yield. Length will also be important as you mentioned.
The formulas from my previous post allow one to make comparisons between tubes loaded in the same manner. For example, if you wanted to compare the stiffness/weight for a steel tube and aluminum tube of identical dimension and loading, the equation would be S/A = ((Es*ODs^2)/(Ls^4*rhos))/((Ea*ODa^2)/(La^4*rhoa). OD and L cancel out since they are the same for this example and you're left with (Es*rhoa)/(Ea*rhos) = (29700*.098)/(10000*.284) = 1.02. So all else being equal, stiffness/weight for steel is 1.02X that for aluminum. In other words, steel and aluminum are nearly identical for this metric. You can use the equations to compare any other parameter of interest. These equations are good for comparisons only - to calculate actual values with units you'd need to know the loading and boundary conditions and then add the relevant constants to the equations.
Moof, nice looking carbon tubes with end fittings!
In the past I've bonded carbon fiber to metal using Hysol 9359.3. I think you'd be fine just using an outer aluminum sleeve bonded to the carbon. The inner sleeve would only be necessary if you had a very high compressive radial load. It is important for gluing carbon to metal that you leave a bond gap for the glue to fill. The bond gap is normally 0.01" to 0.025".
If drilling into carbon, Moof is right on with the diamond coating. You can also use carbide tooling but it will wear faster. Rule of thumb for drilling holes into carbon is to space the hole 4 diameters from the nearest edge. So for a 1/4" hole, you'd want the center of the hole at least 1" from the edge of the tube.
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Plaidman
Trad climber
West Slope of Powell Butte, Portland, Oregon, USA
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Feb 20, 2017 - 06:23am PT
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John thx for sharing all these details. This is really cool stuff.
I'm trying to get one of my design engineer/climbering partner to chime in.
Plaid
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Woody the Beaver
Trad climber
Soldier, Idaho
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Feb 20, 2017 - 08:59am PT
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This is good smart fun! I enjoy reading this thread! Thanks.
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Moof
Big Wall climber
Orygun
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Feb 20, 2017 - 10:36am PT
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I did a batch of the corner pieces for 1 1/8" tubing a number of years back, still have a bunch extra. I am gradually getting a little more free time now that the kid is getting a bit older. I need to get back on the horse and get my hobby room dusted off...
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WBraun
climber
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Feb 20, 2017 - 10:43am PT
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Thanks Moof for the loctite Hysol glue info.
I just ordered the 608 version and will glue Yosemite back together to make it great again ......
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Feb 20, 2017 - 11:24am PT
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Still working on the next installment. One important thing to note about the stiffness/weight formula is that it has nothing to do with the strength of the material. So even though a 1" OD, 0.049" wall 7075 aluminum ledge is stronger than a 1.125" OD, 0.058"wall 6061 aluminum tubing (see above Strength Index chart), we will see that the smaller tubing 7075 ledge will flex more due to its tubing cross-section geometry. Note that all aluminum alloys have similar E values, regardless of the difference in strength.
Getting a grasp on the E value is important. E, the modulus of elasticity, also known as Young's modulus, can be thought of as the springiness of the material. Low E, very springy; high E, very stiff. Rubber bands have very low E, steel has high E. But even though, as edavidso points out, aluminum and steel have similar stiffness/weight ratios, note also that the Outside Diameter of the tubing is squared in the stiffness/weight equation. So theoretically you could make a steel portaledge frame as stiff as aluminum with same weight, but the steel one would have to have a very thin wall to be of similar weight.
That brings another failure factor to consider in portaledge tube design: buckling--with ledge tubing if you make the tubing wall too thin, then a buckling failure mode comes into play (you can see the formula on my titanium notes some pages back). I'm not planning to cover the engineering formulas and analysis for buckling here, but as a rule of thumb, I found that anything less than 0.028" tubing wall thickness, even with a strong, high E material, is too thin for portaledges due to buckling potential after even a tiny dent.
------
John Middendorf
http://www.johnmiddendorf.net
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Feb 20, 2017 - 01:46pm PT
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Maybe some feedback? Are these indexes making sense? Here is the next one.
Note that flex will be determined by the length of the tube, the cross-section geometry, and the material stiffness.
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'Pass the Pitons' Pete
Big Wall climber
like Ontario, Canada, eh?
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Feb 20, 2017 - 03:33pm PT
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"Have I lost everyone? Seems like the thread isn't getting much response lately."
Well, it *IS* a lot of asbestos and marmalade...
I've made it as far as the cubic relation of length to deflection. Makes sense.
[shameless bump to keep this on the front page, will catch up on the rest of the posts]
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Feb 20, 2017 - 03:42pm PT
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Thanks, Pete! Almost ready for the finale on D4 innovation #1 (elimination of the spreader bar on a 'full-size' ledge), so we can then move onto the one you've been waiting for, innovation #2 (corner design).
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'Pass the Pitons' Pete
Big Wall climber
like Ontario, Canada, eh?
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Feb 20, 2017 - 03:50pm PT
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I'm paying rapt attention. Couldn't read on my smart phone, had to pull out the laptop. I need to follow carefully so I don't miss anything.
Have you posted up your Facebook video on this thread yet????
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Feb 20, 2017 - 03:55pm PT
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Ok, here we go:
A few things to note here. First, it is easy to see why Metolius needed the spreader bar--they increased the length of the ledge, but did not re-design the tubing of the frame and thus have the highest flex index of any ledge commercially made (note: I am not 100% certain that they are still using the 0.058" wall tubing--perhaps they have bumped it up). Regardless, the 1.125" OD tubing is just not the right size for a ledge that is longer than 75".
You might ask why didn't I design the Cliff Cabana back in the 1990's with bigger outside diameter tubing, rather than stick with the 1.125" OD with beefed up thickness--well, as I mentioned, we had a lot of infrastructure already invested in the 1.125" corners (made from 1.375" square Aluminum bar stock), and I never really considered the Cliff Cabana a mainstream design--it was really for the 3-person Diamond Ledge, a very specialised tool for high wind situations, where weight might not be a critical factor. My design of the Cliff Cabana was kind of a shortcut--beefing up the tubing thickness to 0.083" made sure it had higher strength and similar stiffness as the proven Alpine Double without having to redesign the whole frame system from scratch. (Note: the original Cliff Cabana was fine with three people without a spreader bar--perhaps a bit more flexy with the additional person, but not overly so. I suspect the reason that BD later adopted the spreader bar was that they also adopted Metolius's open corner system which, as mentioned before, adds to the flex of the system). By the way, I never thought we would sell more than a few Cliff Cabanas, so I am surprised that most of the recent portaledge fame and glory (i.e.full page NYT pictures of Tommy Caldwell on the Dawn Wall) is all about that design.
What you can see here pretty clearly is that the 1.25" OD 0.058" wall is really the best metal tubing of those listed to use for a larger ledge. But an issue with the traditional A5 design now used by BD and Metolius is be that switching to 1.25" OD tubing would require larger block corners, which would significantly increase the weight of the ledge. Something perhaps to note in the discussion of titanium, is that though the tubing weight for our Titanium Great Trango ledge only saved 1/2 pound, one might think it wasn't worth it with all the added flex; but because the corners were much smaller and lighter for the 1" tubing, there were other weight savings and the ledge was very light and compact (for its time). Perhaps one could make a 1.25" OD ledge with drilled out inside corners, like on the Fish, and I definitely considered that when I began looking at making a larger lightweight ledge, but there is a better solution, which I will reveal shortly.
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Feb 20, 2017 - 06:03pm PT
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Ok, so time to wrap this up. I'm going live with a Kickstarter in a week or so, and have to get back to that (and build more prototypes!)--our plans are to offer a limited batch of the D4 Portaledge for September delivery. If you or you know anyone who might be in the market for the world's lightest and strongest ledge, please let them know!
Here is the link that will have all current updates: http://www.facebook.com/bigwallgear/ Please like, follow, and share! (I told you it would be a plug for the D4 portaledge) ;)
The 2017 D4 ledge will have Aluminum tubing. One nice thing about my new design is that it is very adaptable to making a Carbon Fibre version, which I am beginning work on now. But those won't be ready until 2018, and they will be very expensive--at least $1600. As you can see from the specs posted in these past pages, the carbon fibre will be stiffer, lighter, and stronger. It will save a couple pounds. But expensive. The D4 Aluminium Ledge will be more bomber than anything out there today (stronger, lighter at around 6kg or 7kg, and more rigid) and will retail for $1200, though the Kickstarter will offer a limited first batch for a much discounted price for the early adopters.
So, the solution to eliminating the spreader bar? Bigger tubing of course, but how?
Innovation #1 of the D4 Portaledge is a Hybrid Diameter design. Think about where the biggest bending stresses and most flex is on a ledge, and it leads to the answer. Back in a few...
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Feb 20, 2017 - 07:28pm PT
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Ok, here is the solution to eliminating the spreader bar for block corner ledges:
Simply beef up the mid-section of the ledge with the stiffer and larger diameter tubing, while saving weight where the stresses are less on the ends with the smaller diameter tubing. Saves weight on main joiners as well (an important feature of good portaledge design is to ensure the joiner is stronger than the main tubing, otherwise you can get a nasty bend in the joint that renders the ledge unusable).
It might seem like an obvious and simple solution, but I would argue that it came from understanding all the engineering fundamentals, which I hope have explained to everyone in these past posts so they are more easily understood. And I guess it isn't too obvious, or the other manufacturers would have re-engineered their A5 derived designs instead of opting for a spreader bar solution (after all, they've had 20 years to figure this out!).
The Hybrid Diameter design is rigid. Even when set up against a tree, there is almost no flex--as mentioned before, a tree is a very bad loading situation yet I can comfortably say this is really the first portaledge design that is fully suitable for tree camping. Even though I had modelled it extensively with FEA tools before testing a prototype, I had little idea how good it actually is until I actually played with the first pre-prototype last Fall in Yosemite.
Here's a picture of Marek Raganowicz jumping on it at Devil's Elbow. He couldn't believe how light, strong and rigid the frame was! He's heading out with the first D4 prototype to Baffin this week. Note that I have hidden the corners--that is for the next topic which could be called, "Goodbye Block Corners--and Plug for the D4 Portaledge"! ;)
This project started thanks to Chris Trull, who approached me in Arapiles last year and quizzed me about portaledge design. His enthusiasm and positive energy really got me excited to put my mind to work on a better portaledge for climbers, after 20 years being away from the portaledge design business (though I have been tinkering with folding tension fabric structures over the years, and hope to bring some of those ideas to light in the coming years).
I feel happy to be able to contribute to climbers again. My design philosophy is that innovation always precedes jumps in human standards (see Mechanical Advantage), and I hope my new lightweight and compact portaledge design will help more climbers achieve their dreams and extend the limits of human endeavour in the remote big walls of the world.
I appreciate all the input and comments on this post, and again, please help spread the word to anyone looking for a cutting edge tool this year by keeping an eye out for the Kickstarter next week and by staying tuned to the BigWallGear Facebook page.
There are four major innovations of the D4 ledge which are completely new, and they will also be disclosed soon. Besides a new corner system, I've come up with a novel suspension system, and also a way to make deployment and pack-up way simpler, quicker, and more organised. More details in the Kickstarter.
As a last picture, I include this one as a memory to Walt Shipley, who helped with the initial design of the A5 portaledge. The top drawing is Walt's:
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Moof
Big Wall climber
Orygun
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Feb 20, 2017 - 08:07pm PT
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Exciting! Know anywhere I can sell some plasma to?
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edavidso
Trad climber
Oakland, CA
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Feb 20, 2017 - 08:22pm PT
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John, good idea with the hybrid diameter. For a simply supported beam with distributed load, moment and deflection increase non-linearly towards the center so it makes sense to have a larger diameter tube at the center and then step it down to the smallest diameter at the attachment points. I guess the easiest way to do this would be telescoping tubes? I also thought of hydroforming to produce a continuous expanding diameter tube but it would be expensive for small volumes.
Your flex index is the inverse of the stiffness formula I posted earlier, k is proportional to E*d^3*t/l^3. The only difference is that I'm using a thin wall approximation.
Looking forward to the other innovations!
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Feb 20, 2017 - 09:31pm PT
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No, Hybrid Diameter simply refers a combo of commonly available tubing diameters in the same ledge (specifically, with larger diameter tubing where the bending stresses and flex is the greatest, in the middle of each side). Cost efficient as well as light and strong and rigid.
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Riley McDonald
climber
CA
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Feb 20, 2017 - 10:09pm PT
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I have been loving the suspense of reading this... Thanks John!
I think I figured out your joint idea. Without giving too much away, am I right in saying that corners and joints don't necessarily have to be the same? Would make sense also for connections of differing OD tube.
Edit: I think I just saw video proof! Those who want the source can probably find it with some sleuthing... Or wait...
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