Author Topic: Can we measure the nipping force of a loop on the rope ?  (Read 2392 times)

xarax

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Can we measure the nipping force of a loop on the rope ?
« on: July 18, 2010, 12:11:03 PM »
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« Last Edit: December 23, 2010, 03:29:44 PM by xarax »
This is not a knot.

squarerigger

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Re: Can we measure the nipping force of a loop on the rope ?
« Reply #1 on: July 19, 2010, 06:43:14 AM »
Hi Xarax,

I suggest that we could use the plastic strips used for measuring the applied torque to steel-work bolts - these are thin plastic strips of known density and thickness (and therefore known ability to squeeze out) that are slipped between bolt head and washer to allow the torque applier to determine just how much torque is enough.  Would this work in place of Dan's (or anyone else's ) finger?

SR

DerekSmith

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Re: Can we measure the nipping force of a loop on the rope ?
« Reply #2 on: July 20, 2010, 01:29:39 PM »
Good challenge Xarax.

The purpose of the nipping loop is to stop the tail from slipping out, which would allow the knot to unravel.

The amount of nipping force in the loop is not so much the issue as is the amount of retaining force being brought to bear on the tail.

One way to gauge the tail gripping force is to include a couple of small test threads into the nip along with the tail, then dress set and load the knot to create the nipping force - then test the grip by pulling the two test threads in opposite directions until they start to slip out of the nip - the tension needed to pull out the threads is a measure of the grip of the nip.

You could get away with one test thread, but in pulling it you would be adding load in the direction of the pull.  By adding two test threads and pulling each in opposite directions the testing process does not change the test load of the knot.

It is probable that the grip of the nipping loop will vary around the loop, this method of testing allows us to put the test threads into different positions around the nipping loop, so we could measure the grip on different sides of the tail, or even with sufficient diligence we could plot the grip 360 degrees around the tail.

The test also allows us to measure the grip under different loadings or after loadings or flogging.

I agree with crediting the test to Dan and we could define the standard unit of tail grip as the 'Lehman'

Derek