Woodcutter Posted April 3, 2013 Share Posted April 3, 2013 Is it all the same, or is some cord significantly stronger than the rest? I heard about something called tech-cord a while ago? I'm assuming it would be static, but this doesn't really matter. I need to replace some steel cable on a device & cord is the way to go as the steel can't go round corners without stress concentrations & then breaking. Can't be thicker than 5.5mm diam to fit and can take knots. ...AM steel - woven dynema is a candidate. Thanks in advance. Jake Quote Link to comment Share on other sites More sharing options...
rob Posted April 3, 2013 Share Posted April 3, 2013 I would not use dyneema, since I have read much suggesting knotting dyneema is a bad idea due to it's low friction (the knots can work loose) and other reasons. What is the "device" you are considering using cord for? The type of device and it's intended use are important -- nylon cord may go around corners, but that doesn't mean it won't be cut when loaded around a sharp corner. Also, depending on your application, do you need the absolutely strongest cord? Quote Link to comment Share on other sites More sharing options...
tvashtarkatena Posted April 3, 2013 Share Posted April 3, 2013 (edited) Dyneema has a higher breaking strength/dia, doesn't absorb water like nylon, slips a little more (proper knotting can prevent failure here), and isn't nearly as elastic as nylon. Googling will produce a ton of info. Compare the two for your app (static or dynamic). 5.5 nylon is pretty thin stuff to catch a fall with. Edited April 3, 2013 by tvashtarkatena Quote Link to comment Share on other sites More sharing options...
crackers Posted April 3, 2013 Share Posted April 3, 2013 I'm assuming it would be static, but this doesn't really matter. I need to replace some steel cable on a device & cord is the way to go as the steel can't go round corners without stress concentrations & then breaking. Can't be thicker than 5.5mm diam to fit and can take knots. ...AM steel - woven dynema is a candidate. Thanks in advance. Jake Um. This sounds like a recipe for disaster. This seems like it is NOT for a climbing related application. It sounds like it should be engineered, not debated on internet fora. I work closely with a number of cordage manufacturers, and work every day with Dyneema and Kevlar and Technora and Twaron and other high strength exotics used in making cord and fabric. I'd recommend, strongly recommend, getting in touch with manufacturers directly. climbing/life safety technical: sterling rope. bluewater. pigeon mountain industries. industrial / mooring: samson ropes pelican Also, its not recommended to knot Dyneema. It slips under a very light load. Good luck! Quote Link to comment Share on other sites More sharing options...
tvashtarkatena Posted April 3, 2013 Share Posted April 3, 2013 The OP is inquiring about cord, not slings. You can (carefully) knot dyneema cord safely. Quote Link to comment Share on other sites More sharing options...
ryanb Posted April 3, 2013 Share Posted April 3, 2013 Agree that this sounds sketch depending on what this device is for. That said check out these (now old) test results: http://user.xmission.com/~tmoyer/testing/High_Strength_Cord.pdf Spectra (similar to dyneema) looses a lot of strength when knotted (or, I believe, repeatedly bent) so I wouldn't expect it to be an improvement vs steel. Nylon holds up better but is weaker to start with. Quote Link to comment Share on other sites More sharing options...
rother Posted April 3, 2013 Share Posted April 3, 2013 Clearly the application is quite important. Without knowing more about it's potential use, it's hard to say if substituting dyneema/spectra is appropriate. Putting knots in dyneema/spectra significantly reduces the strength of the loop/cord, especially at the knot. The material is also static. No shock loading or it'll snap in a jiffy. Static loads are okay, and a triple fishermans knot might prevent the knot from slipping. Again, application. Quote Link to comment Share on other sites More sharing options...
Woodcutter Posted April 3, 2013 Author Share Posted April 3, 2013 Thanks everyone. It's a cable-stay to hold a lever-arm. But it's holding the lever at the bottom, the cable comes down the lever and under the pivot fixed, large diameter (1") rounded end (really sorry no drawing right now, and is tied off. SO the leverage is great. Assume 200lbs pushing the lever forwards with the lever being 300mm long. The lever is subject to jerky loads. Knotting is the easiest way to fix. Thanks for looking at my problem, I'd get it engineered, but then we're talking real money. Thanks again, you guys are great. Quote Link to comment Share on other sites More sharing options...
Woodcutter Posted April 3, 2013 Author Share Posted April 3, 2013 (edited) Also Ryan B, the BD article is great, thankyou. Also HIllmap Rocks! It seems that 6 or 7mm nylon is the best bet. Edited April 3, 2013 by Woodcutter Quote Link to comment Share on other sites More sharing options...
tvashtarkatena Posted April 3, 2013 Share Posted April 3, 2013 Post a sketch. I have a hunch what your problem might be, but can't really discern what the system looks like from the description. Quote Link to comment Share on other sites More sharing options...
Woodcutter Posted April 3, 2013 Author Share Posted April 3, 2013 http://jakeevans.smugmug.com/Washington/Buffer/28742499_92KJSd one day I will work out how the photo's work on cc Quote Link to comment Share on other sites More sharing options...
tvashtarkatena Posted April 3, 2013 Share Posted April 3, 2013 (edited) I assume 200lb is the load. Don't know if this mod is possible, but here's one way to reduce the stress on that stop line if that becomes necessary. Running the stop line under the pulley and tying it off the the left might even be better if the minimum angle (the larger the better) isn't breached. The force on that line is 200lb x 300mm/pulley radius the way its built right now. If this is too elaborate, increasing the stop line pulley radius (see above) would help. Or you could just reverse the system and put the load on the stop line - putting another stop line on the top end of the lever. Load on the load line would be 200 lbs, the stop line quite a bit less. You'd also get much less travel, though. Cables often break at one of the ferrules (crimp points). Make sure the angle between the two cables as they come together at the ferrule is 60 degrees or less and use the proper size crimping tool for the ferrule might also solve your problem if that's what's going on. Edited April 3, 2013 by tvashtarkatena Quote Link to comment Share on other sites More sharing options...
Woodcutter Posted April 4, 2013 Author Share Posted April 4, 2013 That looks excellent Mr (or Mrs) Tvash. I will surely post pics if the gadget works. Thanks again, I'm off and running. Now I just need a laser cutter, and a few hours on the router and some luck. Cool. Jake Quote Link to comment Share on other sites More sharing options...
tvashtarkatena Posted April 4, 2013 Share Posted April 4, 2013 Don't sue me if it breaks! Best of luck, brah. Quote Link to comment Share on other sites More sharing options...
Woodcutter Posted April 4, 2013 Author Share Posted April 4, 2013 I'm English: Suing is a sign of poor character. My sister fell down a lift shaft at work & didn't sue. If you're dumb enough to screw up, you take the pain & maybe it won't happen again. I think Darwin would probably agree. Quote Link to comment Share on other sites More sharing options...
tvashtarkatena Posted April 4, 2013 Share Posted April 4, 2013 (edited) What does this contraption do? I'm picturing a forlorn pyrate suspended over the Thames in an iron maiden, but that would probably be more than 200 lbs. Edited April 4, 2013 by tvashtarkatena Quote Link to comment Share on other sites More sharing options...
Woodcutter Posted April 4, 2013 Author Share Posted April 4, 2013 ..can't tell you right now, soz. Give it a few months to ferment & it'll be ready for consumption. Quote Link to comment Share on other sites More sharing options...
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