UKC

Basically.. is it safe to extend the tape loop of a cam with another piece of tape, thus eliminating the need for a quick draw. A tape on tape situation! This was discussed with a couple of mates and we failed to come to a conclusion...

In reply to Paul Crusher R:

using a larks foot I assume?

In reply to CurlyStevo:

An overhand knot in a sling or a tape knot used to make a loop would be a 'tape-on-tape situation', so I would say that these rules should be intelligently applied.

In reply to Paul Crusher R:

You probably won't die.

But with tape on tape, or dyneema on tape, things can move fast and generate a lot of heat if they're allowed to move too freely. You wouldn't want things to get melty. I suspect thats unlikely though.

Depending on what method you use, there's also the (potential) problem of you, or someone using your cam, somehow managing to clip into the wrong bit - one end of a larks foot? - which might kill you.

In reply to Andy Morley:
I don't think a knot is necessary or a good idea in this case. The sling could easily be threaded through the tape on the cam and then you clip both sides of the sling. The two knots mentioned (lark's foot, overhand) weaken sling material by about 50% and provide no extra security.
The only benefit to using a lark's foot is that there is more "free" sling length, which is useful if forced to use a short sling around a fat rock thread.

Edit: it seems the OP wants to pre-lengthen the cams' to avoid faff on the route. In that case disregard what I wrote above.

In reply to SenzuBean:


I've heard about recent research on the susceptibility of both Dyneema and nylon slings to break under shock-loading from an 80 KG weight dropped just a few feet. Having looked at some of it online, there seems to be a lot of interpretation around the results of test, possibly misinformed, as to how overhand knots may actually improve sling performance in nylon due to their absorbing some of the forces.

My gut feel is that because these tests are more complex than they might appear, climbers are taking the reports and making conclusions that are sometimes mistaken. Is there anyone who is well-informed on this, who can offer a really authoritative view and who is willing to share their knowledge?

In reply to Andy Morley:

Here's the tests:

http://dmmclimbing.com/knowledge/how-to-break-nylon-dyneema-slings/

In reply to SenzuBean:

Yeah - I had seen that page.

In reply to Paul Crusher R:
Your harness is various lengths of tape threaded through each other and sewn into belt/belay/leg loops so tapes applying large forces to tapes is nothing new.

According to a random person on the internet (me), tape on tape to avoid caribiner loaded on an edge should be fine, otherwise use a caribiner.

In reply to Paul Crusher R:

use a basket hitch with a longer sling (thread it through and clip both ends)
(see dmm site for videos and stats)

job done.

In reply to lithos:

Ah - basket hitch, not heard that name before. It's what I tried to describe

In reply to Paul Crusher R:

If I'm understanding what you're describing correctly, it sounds similar in principle to the Metolius PAS*, which is perfectly safe. Obviously, that comes with the disclaimer that Metolius will have done a lot of testing and may have found that only particular widths of particular materials are safe to use in this manner.

As far as I can make out, the issue with "tape on tape" would be mainly due to friction causing heating and I can't see any reason why that would occur to any great extent with your proposal (though it seems like the reason why girth hitches/larks foots would be a potentially poor idea).

* http://www.metoliusclimbing.com/images/PAS-22-blue-yellow.jpg

In reply to Paul Crusher R:

Why not make it long enough so that you do not need an extender,but do it avoiding a tape on tape arrangement? remove the (short) tape supplied,replace with a loop as long as you think it needs to be,tied closed with the correct knot?

In reply to nickinscottishmountains:

That's what I was I thinking, perhaps tied as a twisted double loop so you can shorten or extend like a DMM Dragon cam.

In reply to nickinscottishmountains:

Some careful thought still needs to go into that, depending on the type of cam. I believe DMM encountered an issue with narrow tape cutting through the loops of cams under high loads.

In reply to Luke90:

This rings a bell actually. And looking at my DMM Dragons, the slings thread through a fairly complex forged bit of metal, which makes me think some careful design has gone into it. I also remember seeing BD cams with a an extra non-load-bearing bit of sling wrapped around the thumb loop inside the load bearing sling. If I recall correctly, that was to stop the sling damaging the wire (or vice-versa?) in a fall.

So yes, people putting their own slings on cams should make sure they get it right.

Edit: relevant link about changing slings on BD cams:
http://eu.blackdiamondequipment.com/en/qc-labthe-dangers-of-modifying-your-...

In reply to Jack B:
I'd be wary of the pinching effect of single layers of sling as shown in the bd link above. In harnesses the tape is either much thicker than a sewn sling or wider (or both) which would prevent this pinching and failure. There are examples of harnesses and slings/daisy chains failing when larks footed to belay loops. I remember reading into this on Supertopo when interested in re slinging my camalots, I think in the end they suggested the best way was to re-thread on cord.

In reply to CurlyStevo:



Why assume that?
A loop (basket hitch is the obvious way to go and perfectly safe).

In reply to Andy Morley:



This has nothing to do with the original post.

In reply to elsewhere:



At last some actual sense. Belay loop on a harness a 'tape on tape situation' (sounds scary when you have a phrase for it)

In reply to Luke90:


You seem to be confusing a few things.

1, The op is asking if it's ok to extend the existing tape on the cam using a sling (presumably then using the Krab on the cam for the rope) to save a quickdraw. Not replacing his tape with longer tape.

2, DMM experienced issues with thin dynema cutting through the Camalot style thumb loop so used their current set up instead so you only have to worry about this if you substitute thin tape for thick tape on a Camalot (but you may be wise to avoid putting thin tape slings directly into the thumb loop of a Camalot) Still doesn't apply to the O.P.

In reply to Luke90:

Not exactly huge thought needed, use the same width loop, maybe even by the same manufacturer?!?

In reply to DubyaJamesDubya:

I understood the OP perfectly, thank you. You might want to examine the reading comprehension plank in your own eye

I was specifically responding to the suggestion by nickinscottishmountains that OP replace, rather than add to, his tape loop. I think that's pretty clear, especially since I quoted that suggestion in my post.

In reply to nickinscottishmountains:

Not rocket science, granted. Just thought it was an issue worth pointing out since it's non-obvious, in my opinion. Certainly wouldn't have occurred to me if I hadn't read DMM's thoughts on the matter.

I'm also not completely certain that using the same width tape is a trivial solution. I haven't used any cams with this style of loop (mine are all tech friends) but my impression from pictures is that the manufacturer fitted tape tends to be fairly wide and fairly stiff which I don't imagine would lend itself well to knot-tying. Not a problem for the manufacturers when they sew the loops.

In all likelihood, OP would never apply forces large enough to cause breakage, even with thinner tape, but I wouldn't be entirely surprised if a decent fall on thinner tape deformed the loop (as pictured in the DMM article linked above).

In reply to Paul Crusher R:

Nish one.

Yes I was getting at the friction / continuous wear issue, this was the others concerns. And yes I'd heard there were some issues with different tape sizes causing problems. I also am inclined to steer clear of anything larks foot wise, these are proven to weaken by 50% I believe.

The said cams not dmm but wild country 2014 models have a short 4 inch sling off the cam, the problem is the bigger cams hang way too low for me off a harness when clipped in the normal way, and as the sling is hard sawn you can not clip the cam directly to shorten the length. They've changed the model last year and switched to the doubled up slings.. dmm style, which eliminates this.
Maybe I should bite the bullet and chop them and fit a doubled up sling, double fishermans knotted as someone suggested as the best solution.

In reply to Paul Crusher R:


Dyneema tied with double fisherman's is quite weak (dyneema melts easily, so when the knot cinches up in a fall, high heat is absorbed, melting the dyneema at contact points - acting as a lubricant, or so the hypothesis goes), so to be by the book, stick to nylon/tech-tape for the loop.

Here's some more data on the subject: http://dmmclimbing.com/knowledge/knotting-dyneema-vid/
Dmm saying this in there: "Overall, we should stress that we strongly recommend that you do not construct your own Dyneema® slings by tying lengths of loose Dyneema® tape together."

In reply to Paul Crusher R:

That should be mitigated to a large extent by the cams (presumably!) very rarely being loaded.


The issue with the loop kinking and potentially cutting the tape isn't restricted to DMM models. People keep referring to DMM because they're the manufacturer that have talked and blogged about the issue. As you say, Wild Country have switched to a slightly narrower, doubled sling on the 2015 models but I don't know whether they also changed the loop design to compensate for that.