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Moof
Big Wall climber
Orygun
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Mar 30, 2017 - 04:59pm PT
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Yep, the vertical fibers of the fabric help spread out the load for sure, but that is well beyond first order statics that I can hope to tackle. If you want to get pedantic the fins should be catenaries (asymmetric ones at that) to provide equal tension along the length of the fabric for a point load at the apex. But at that point you are jumping the shark pretty badly.
I'm looking forward to getting an hour or so of tinkering time this evening after kiddo's bedtime to pencil it all out better.
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Mar 30, 2017 - 05:45pm PT
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Interesting you bring up catenaries--my first prototype I did indeed design it with a catenary, but it turns out the longitudinal stiffness of the webbing on the edges prevents the edge from taking the load like a catenary--hence the straight lines on the support fins. The interior shark fins, however, still are designed with catenaries.
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Todd Eastman
climber
Bellingham, WA
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Mar 30, 2017 - 08:44pm PT
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Wind's shifting, getting smoke in my eyes...
... great campfire!
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Moof
Big Wall climber
Orygun
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Mar 30, 2017 - 09:17pm PT
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So I get to the angles pretty easy.
Since you can assume equal force on the two straps at A and B, the angle relative to the main strap is also equal. The force multiplier is 1/cos(180-alpha), which works out to 33.6 degrees for a 1.2:1 force multiplier, or 67 degrees maximum total angle of the fin. I am guess you rounded to 60 degrees?
The angle of the main strap works out to about 21 degrees, so the would for out to an angle of 9 degrees off vertical at B, 51 degrees from vertical (39 degrees from the bed) at A if using 60 degrees for the fin angle.
Sound about right?
Still need to figure out the height of the fin, but my eyes are trying to close on me.
Unless you wrapped the webbing around the fin edge taco style before stitching, I don't know how to get around the stiffness to get a catenary, but again, that is just overkill to begin with.
Edit:
Looking at the pics it looks like you chose 45 degrees, which would put the B point within rounding error of 0 degrees, making much more sense than 60 degrees. Force increase would be just 1/cos(22.5)=1.08, or less than 10%. Ideally the fabric would be cut on a 22.5 degree angle, but that is pretty wasteful for a marginal increase in load spreading. My in-process Ghetto4 ledge will shamelessly copy this approach, though I am aiming to only put bed tensioners on one end to simplify/lighten.
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D-Rail
Trad climber
Calaveras
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Mar 30, 2017 - 09:17pm PT
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Looks amazing Deuce!
I have an Alpine Double that is well traveled. It is probably from about the same vintage as your Jumars. Months of detailed work to update the portaledge and you still roll with the old trusties?
Keep it coming. This is great stuff!
Daryl
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Mar 31, 2017 - 06:42pm PT
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Last day to order your Expedition D4 Portaledge on Kickstarter!
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Apr 1, 2017 - 07:58pm PT
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The new D4 Zippered Door Design has gone from concept (imagined while climbing Ozymandias) to first functional prototype in a couple weeks! This new door and vent design will be sent out to Twid Turner this week for full conditions testing on a big wall in Alaska.
There's only 12 hours left to order a D4. I have been open with the design process so all can see how the innovation has progressed, and if history is any guide, these new concepts will be widely copied, but the original is always the best! Thanks for your interest! Cheers, John Middendorf.
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Apr 2, 2017 - 02:12pm PT
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The Kickstarter has successfully ended at 150% of goal! Many thanks to everyone who supported this reinvention of the modern expedition Portaledge. We will continue our product testing and begin production in the coming months.
We have already gotten new requests for orders for the D4 portaledge. Of course we will fulfil our Kickstarter orders first, and will set up a waiting list for future orders. All Kickstarter orders are expected to ship this year. Thanks again to all!
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Moof
Big Wall climber
Orygun
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Got inspired for my own hobby ledge. Ordered up the crap and I am now assembling.
First step was to cut most of the tubing (one piece is still in transit). Never used a tubing cutter on aluminum, so much easier, cleaner, and nicer than hack saw and files. Who knew?! Next step was to start glueing things up (less eorror prone than rivets for me).
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BLUEBLOCR
Social climber
joshua tree
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NICE Moof!
On those glued up ends, looks like you got female receptors waiting for male tube insertions?!
I was jus wondering how might a male stub(maybe an inch long) would be comparably in strength, and set-up?
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Moof
Big Wall climber
Orygun
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These corners were originally made for carbon fiber tubes, and I was paranoid about the ends splintering/crushing after abuse, so the recepticle is a full 1.5" deep, about 1/8" wall thickness. It should provide some of the rigidity Duece is getting from his curved corners. I have my corners on the end tubes instead of the side tubes, cuz I always have to learn the hard way... We'll see how that works out shortly, but it is how my carbon ledge is set up.
I honestly don't know whether male or female corners ultimately hold the best strength/rigitity/weight optimization. It is something I have pondered a few times to no avail.
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Moof
Big Wall climber
Orygun
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Loks like the fabric place sent me 2x the fly material. The roll was alarmingly heavy, but it looks like they sent me 12 yards instead of 12 half yard like I ordered. Bonus! Not sure what to use it for however.
I am planning to see if I can't add some pockets INSIDE the center fin between the two layers (mine is a 2 strap with a catenary in between, fabric weeve on the 45 for better force spreading). Need some place to stash crap, you know?
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WBraun
climber
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Looks good Moof.
With your new portaledge and your new valley giants you'll be the bomb ......
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Apr 9, 2017 - 08:52pm PT
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Nice, Moof.
Another trick for tube cutting I recently rediscovered is using a step drill to do the initial deburring after using the tube cutter.
Just something like this--has the right taper, gets a nice initial inside debur.
Of course having a regular deburrer is key as well:
What kind of glue are you using for the aluminum? I have some concern about the expansion/contraction in colder temps, but would be interested in hearing more about gluing vs. riveting.
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Moof
Big Wall climber
Orygun
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Apr 10, 2017 - 06:40am PT
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Same Hysol 9340 I had leftover from my carbon fiber project, been storing it in the freezer. A aircraft home builder recommended it some years back. For glueing up Al to Al the TCE mismatch is essentially zero.
I'll have to get a proper deburr tool, I have been just carefully using a utility knife. No bueno. Never thought to use one of those step drills!
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Apr 10, 2017 - 02:26pm PT
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Slow speed is the key for the step drill, no more than 500rpm. There are speciality tools for chamfer and deburring tube edges, but very expensive. Step drills are cheap and readily disposable when they get blunt.
For a non specialty tool system for the outside edges of tubes that get inserted into another tube in the design, I use a belt sander and hold the tubes while spinning them and change the angle to get a nice rounded edge. Then about a minute or two steel wool polish by hand.
Having an air blower, even just a can of compressed air, is also a key tool for making frames, as even the most invisible spec of aluminum shaving can cause problems in the joints. Or you could use some sort of cloth to push all the way through the tubes to ensure fully clean.
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BLUEBLOCR
Social climber
joshua tree
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Apr 10, 2017 - 03:03pm PT
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Moof👌👍
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Moof
Big Wall climber
Orygun
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Apr 10, 2017 - 04:54pm PT
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Werner,
Goal is to be the best dressed Toprope Tough Guy in the valley!
I should drag my junk show up Royal Arches and get the first 8 day ascent. Unless Chongo already beat me to it?
[Click to View YouTube Video]
Edit: Hey, the narrator at 0:12 looks awfully similarly to my actual partner...
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Moof
Big Wall climber
Orygun
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Apr 11, 2017 - 04:45pm PT
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As previously stated, I have to do things the hard way, and can't always let myself learn wisdom for others until I have thrashed through the briar patch myself.
So back to suspension fins, and catenaries. I can't quite let that one go yet.
Guess what? Mistake #1 before I got re-started.
Not a catenary! Using the webbing for the suspension fin is akin to a suspension bridge, with equal loading per unit horizonal length. A catenary is the shape for equal weight per linear unit along the length of the curve (i.e. natural curve of a chain vs. Golden Gate bridge).
So the correct shape to start with is a parabola. Who knew?!
Next, the loading is at ~22.5 degrees to the bed, so really you have 2 back to back parabolas that are then rotated by 22.5 degrees to make everything make sense, so you get an ideal fin shape for equal weight distribution along the length of the bed like this (part below 0 would be trimmed off):
Actually getting the suspension bridge effect requires the weave to be rotated by 22.5 degree when cutting the shape. As Duece noted, actually getting webbing to follow the shape is a different story, but I had to finish scratching the itch from a couple weeks back.
Next up: My center fin will really be an overlapped cable stayed bridge prototype, not a catenary or parabola. Stay tuned...
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Apr 13, 2017 - 10:46pm PT
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Looks really nice, Moof. Are you going for fin supports for your ledge?
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