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Use Climbing rope double up as braided as 1.5" Gym Climbing rope. What type, diameter rope, No of Strands?
Found these sample videos but curious to know what would be the best way to do this?

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Yes, it's very common to braid a fast rope for climbing out of old rock climbing rope, however the key word there is old. You would typically use whatever retired climbing rope you can get your hands on, as purchasing new rope specifically for this would be very costly.

If using rock climbing rope, the the type, whether static or dynamic, dry treated or not, is unlikely to make a difference. The loads on such a rope (1/8 bodyweight per strand of an 8 strand braided rope) are so low that any stretch in the rope itself will be negligible.

The one thing that would make a difference is the rope diameter, as an 8mm rope would obviously lead to a braided rope 20% narrower than what you'd get from a 10mm rope. And I would estimate that a 10mm rope in an 8-strand braid would get you close to 1.5 inches final diameter.

You could use polyester rope if you really need it to be less likely to absorb water, but unless you're using it to climb out of the ocean, I can't imagine that would be a concern. If you do use polyester, make sure the rope you obtain is double-braided rather than twisted, as the latter will be much less comfortable to grip. (Double-braided is a sheath and core construction, similar to the kernmantle design of rock climbing ropes.)

Making the braid without cutting the rope is also possible, but limits your options, would be less neat and harder to work with. Are you really going to go to all the effort of braiding it just to undo the rope and use it for something else later? Much better to just get a used rope for cheap, and braid it with no intention of even undoing it.

It sounds like you've already figure out how to braid it without cutting, but here's an image to illustrate it. (Click to enlarge.)

Thumbnail

This approach requires that you follow the pattern for a four strand round braid, but using a pair of strands instead of single strands, thereby doubling the total number of strands to eight. The final product will have strands always running in pairs.

An alternative pattern that you could use if you cut the rope is to do a proper eight strand round braid, where the strands are braided individually instead of in pairs, resulting in a smoother, more evenly round final product.

  • Such a lovely answer covering nearly all facets of issues around the question. Reminds me of how I write answers :). One supplementary question - My search shows "rock climbing" "kernmantle" rope as largely Nylon and not Polyester - Do those even exist? – Alex S Jul 29 '17 at 12:47
  • Referring to Liams last bullet point - How much of a concern is it? – Alex S Jul 29 '17 at 12:51
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I'm guessing you mean a rope like you get in school gyms, not climbing gyms.

I wouldn't say any climbing rope is a good choice here. Quite a few problems:

  • Dynamic rope stretches, this is going to make using it hard
  • You'll get nasty rope burn, hemp rope is used for this because it's a lot softer
  • It'll possibly add all sorts of twists in your rope
  • It'll possibly degrade your rope, I'm not sure I fancy using a climbing rope in this manner, all those strands rubing together may make it unsafe. At the very least it's going to make it "fur" up. Generally, don't use climbing rope for anything but climbing.

If you are going to do this I'd try and get hold of some retired rope (possibly from a climbing gym) and/or some static rope that isn't going to stretch that much (the kind used for setting up top ropes not for actually climbing on). Or better yet some soft hemp rope.

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    Dynamic rope will not stretch significantly when the load per strand is 1/8 of bodyweight. Climbing rope is plenty soft for climbing, far softer than sisal which is also commonly used in this application. Besides, softness has nothing to do with rope burns, which come from movement across the rope. Twists are also not a concern, as the time it takes to untwist a rope is trivial in comparison to the time it takes to braid one. Hemp and other natural fibres are likely to be inferior to climbing rope, as they tend to come in a twisted construction, which is less comfortable for climbing on. – David Scarlett Jul 27 '17 at 14:50
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    time it takes to untwist a rope is trivial Really? You've not been pulling your hair out because your climbing ropes twisted and your trying to belay and it keeps getting jammed. Getting all the twists out of 60m rope is hard long winded and potentially a safety issue. All I'm really saying here is, I wouldn't do this with my climbing rope and then use it for climbing. I don't know all the forces involved. Would I want to risk that? No – user2766 Jul 28 '17 at 7:47
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    Untwisting a rope is as easy as pulling the entire rope length through an anchor. Definitely trivial in comparison to the hours it would take to make and then undo an 8 strand braid, and untwisting is something you'd do before you started belaying with it. But the work of braiding and unbraiding is so onerous that no one is actually likely to do this with a climbing rope still used for rock climbing, and even if someone did, the twists would be noticed at the very latest when flaking the rope, certainly not mid-belay. – David Scarlett Jul 28 '17 at 8:10
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    The OP wants to. so its usable when undone as well – user2766 Jul 28 '17 at 9:34
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    The OP may have stated that they wanted to be able to undo the braid and re-use the rope, but it's much more likely that they'll abandon this idea upon realising how much work it is. And there is no reason at all to think that they're going to undo a braided rope and then use it for rock climbing, when OP does not even appear to be a rock climber. – David Scarlett Jul 29 '17 at 2:55

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