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Does cutting a dynamic rope weaken it?

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danielmoss 20 Sep 2011
I was recently in a Cotswold Outdoor shop and they told me that i should never cut a rope at home because the sheath and the inner could separate. They told me that the rope cutter used by the manufacturer cut from all sides of the rope simultaneously and thus somehow avoids this problem but i know that people regularly cut their ropes with hot knifes. What do people think of this?
 stewieatb 20 Sep 2011
In reply to danielmoss:

The rope cutter in the shop and at the manufacturer is a "hot knife". It's a piece of wire heated up by electrical resistance until it melts the nylon on contact, cutting the rope and melting core and sheath together. At home you can use a literal hot knife - a cheap kitchen knife heated in a gas flame (it ruins the temper of the steel, so don't use your favourite chef's knife).

In any case, a separation of core and sheath for 5mm at the end doesn't matter one jot in terms of the actual strength of the rope, especially as there will nearly always be a knot in the rope between the end and the bit being weighted. The core and sheath aren't magically attached together along the length of the rope either, and they can move relatively over time - it's known as sheath slippage, it's not particularly unsafe but it's unsightly and can make a rope hard to coil.
 EddInaBox 20 Sep 2011
In reply to danielmoss:

The sheath isn't attached to the core over the entire length of the rope between the two ends, if it's going to slip then it doesn't matter what has been done to the ends it will bunch up, obviously this would be a pain and if it got too bad one would cut off the end so one could work the excess sheath off the tip and cut it off and reseal the end. The only real advantage is that a neatly cut and sealed end shouldn't fray and it is a little tricky to do it well at home but not impossible, as a point of interest (or not) Mammut use a supersonic welding process to join the core and sheath over a short length at each end though.
 abbotsmike 20 Sep 2011
In reply to EddInaBox:

And then of course there are the new beal unicore ropes, where the sheath and the core are bonded with a bed of glue along the entire length. They are currently the exception, not the rule however.
ice.solo 20 Sep 2011
In reply to danielmoss:

youve been fed crap.

cut it with a heated blade like said above, or a heated pair of shears if youre feeling hi-tech.
take a moment too to round off the ends so it threads nicely.
 MJ 20 Sep 2011
In reply to ice.solo and the thread in general: -

Or cut it with a knife and seal the ends with a fag lighter.
dan 20 Sep 2011
In reply to MJ: Exactly what I was gonna say!
 CurlyStevo 20 Sep 2011
In reply to danielmoss:
It's crap like this which give an otherwise fairly well staffed retailer a bad name.
 Reach>Talent 20 Sep 2011
In reply to EddInaBox:
(In reply to danielmoss)
as a point of interest (or not) Mammut use a supersonic welding process to join the core and sheath over a short length at each end though.


Ultrasonic perhaps? Although I suppose you could use a supersonic stream of air and rely on the resultant heating effect I'm not sure it would be reliable.
 EddInaBox 20 Sep 2011
In reply to Reach>Talent:

Bah! It was late... I even looked it up to make sure I had remembered correctly:
http://www.mammut.ch/en/ropes_quality_wherethedifferencelies.html
 mlmatt 21 Sep 2011
In reply to CurlyStevo:

> It's crap like this which give an otherwise fairly well staffed retailer a bad name.

I do hope that this was a sasarcastic statement?

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