For those of you testing knots, how are you constructing your pulley systems?

[TMCD]

We've recently seen quite a bit of testing going on with small cordage, how are you and others who've got homemade devices doing this? I've got multiple blocks, two rated at 750lbs apiece, I guess I could use these as my testers.

I guess I would need a strong overhead beam or support to anchor the top block and a hook anchored in concrete for the bottom block? What are your homemade devices and how are they setup so you don't harm yourself? I'm ready to do some testing, I don't like how some of these tests I've seen have been conducted and the knots aren't tied to my standards.

[James Petersen]

We've recently seen quite a bit of testing going on with small cordage, how are you and others who've got homemade devices doing this?

I guess this inquiry is directed at me. You can find the description of my testing procedure at: http://igkt.net/sm/index.php?topic=4150.msg25952#msg25952

I'm ready to do some testing, I don't like how some of these tests I've seen have been conducted and the knots aren't tied to my standards.

Please do begin testing.  It would be wonderful to have others confirm or question my results in the same or larger line based on test results. But if you do, be warned, your neighbors/friends/family might get it into their heads that you have gone slightly (or completely) off your rocker.

BTW, which tests was it you had issues with, and what were the issues? Also, please clarify how the knots might be tied to your standards.

[TMCD]

It's not directed at you, it was someone who actually has done a very good job testing various knots but there were several knots I wanted tested that he didn't have time to do. I phrased that poorly anyway, he's done a damn good job. I'm just interested in knowing how someone would go about doing this...I know Dan has said in the past that he had a pulley system device that he didn't care for but did test on it.

[knot4u]

For Truck Hitches, I use a dangerous method I don't recommend for others. LOL

You need a strong floor anchor and a strong ceiling anchor.  You could also send the rope across your car like your tying down a load.  Make a loop in the working end to put your foot.  You can apply some or all of your weight.  You can also bounce up and down.

You can imagine the danger.  Accordingly, don't be like me.  Don't try it.  You have been forewarned.

[knot4u]

We've recently seen quite a bit of testing going on with small cordage, how are you and others who've got homemade devices doing this? I've got multiple blocks, two rated at 750lbs apiece, I guess I could use these as my testers.

That weight seems excessively high for a homemade testing system.  I would only mess with that kind of weight in a controlled laboratory that had redundant safety mechanisms in place.  Diff's poly rope in the Trucker thread looks to be rated at about 50 pounds max.  You don't need crazy weight to test with that rope.  To me, it looks like Diff was applying a load manually.  I could be wrong, but I'm confident I could easily manually apply the load in his videos regardless.

[TMCD]

I wouldn't dare test anything over thirty-fiftylbs breaking strength, it's to scary. I was just pointing out that I do have two snatch blocks rated at 750lbs apiece but I've also got some smaller ones rated at 100 and 300 lbs. I still don't have a good enough idea of how to go about setting it up, I can't try your method unless I'm ready for divorce court.lol.

I do have a pole barn I just built and I could reinforce one of the trusses and that would be a good option and probably my only option.

[Dan_Lehman]

Just some quick comments ... :

1) My "testing" amounts to putting what I regard as
"serious force" onto knots tied in real rope, so as to
gain some idea of what they do --what geometry
is obtained, whether it jams, or whatever.  (And,
re jamming, I work up to "serious" force by steps,
as I do not care to have to labor to untie a really
jammed knot!  So, those getting pulley treatment
must look half-decent by lesser loadings.)

.:.  I've not done break-testing by my own means,
very much.  (But I could do so --and have done--
for plastic binding tape (such as are ubiquitous around
copier-paper boxes and the like), and fishline or some
other tiny stuff.)

.:.  Well, I've not break-tested intentionally, but have
had (a) some specimen (or two?) break accidentally,
and (b) the pulley line break (aided by running over
the pulley wheel or side --so, "cut" in a sense), and
these events weren't terrible.  They'd be less so were
they anticipated!

2) I don't think that you need be put off  by fears of
physical consequences of break-testing small stuff
--e.g., up to 5/16" utility line.  You can take measures
to guard things and keep parts from flying all over;
the break forces should be, I'll estimate, at about
half of the pulley's rating (and esp. if that's a safe
working-load rating, you're fine!).

3) You might arrange more of a test bed with the
pull being horizontal --giving you easy, ground-level
access to all parts--, maybe pulling some small weight
(20#?) as dead-weight resistance to keep things from
flying apart on rupture, assuming you're using rope
in the pulley that isn't terribly elastic.

And assuming that your test method is intended in large
part to explore how/where knots break, you can avoid
having to somehow come up with calibration.  Here,
having two knots in the specimen ensures that you
have a survivor (presumably the same) that you can
examine in comparison with the broken one, in an
effort to understand where & why breakage came.
I marked some specimens sent away for real testing
with threads : white at points where all *limbs* (i.e.,
eye legs, tail, & SPart) left the nube; pink at a point
where I guess rupture would occur, and gold at a
point *downstream* of the pink (which point often
was moved in knot compaction to where pink had
been).  Knots were pulley-set by me and tied in
HMPE, so I'd the advantage of getting little change
in position by material elongation --just further
compaction and then slippage if any (nope!)--;
my 500#? force was remote to breaking forces
of about 2 tons (4_000#)!  With more elastic material
--just about anything else--, one might adjust markings
of rupture-point guess, or add a 3rd.  --simple stitching
through surface fibres, pretty much.  (Maybe Sharpie
marker is okay, despite concerns about potential
influence of the marking itself on strength --some
bright dots here and there aren't likely to upset things
much (on white/yellow line, in red/black/blue ink).

Breaks should start at insides (concave part)
of bends, not the sometimes-mused outer (convex)
part --where maybe fibres need to stretch more,
but CAN, while inner ones are hard-pressed to move
with loads of force upon them.

Or maybe by you aim to do testing A-vs-B for some
general ordering of strengths (although beware that
this takes repetitions and can be misleading if only a
few tests are made; consider : result of 4 vs. 2 seems
consequential, but if 7th test made it 4 vs. 3, then
would you think the same thing?!).


The obvious set up with two blocks is a 2:1
loading the other 2:1 for 4:1 advantage --if these
are single-line blocks.


A camera is good, for pre-testing, and maybe some
shot during testing when you are safely shy of the
rupture force --I think you'll have an idea of when
you've got a "serious" load on them but that they
shouldn't be near rupture (and parts flying from
such a rupture should go away from you if at that
point).  It might well be that most of the geometry
is set by this point, beyond some turns getting
tighter and so on.


--dl*
====

[Dan_Lehman]

I should add:

long ago I had some common, 0.25" nylon line knots
tested by another; it was 3-strand laid line, and most
of the knots broke 1, sometimes 2 of the strands and
then the machine-loading stopped --one should note
that steady-rate machine loading might not match
the sort of in-practice/actual loading expected (say,
of an abseil-ropes joint that capsizes, giving then a
sort of "shock" load, not a slow take-up);

and one accidental break came in 3-strand and also
broke just one strand, IIRC.

** An advantage in this is that one has some hope
of following the path of the broken strand to see where
it lay at the point of break (hence my assertion that it
is at the inner part of a bend, not outer).


--dl*
====

[agent_smith]

I use commercially pre-engineered devices. In my case:
[ ] a 2 ton lever hoist
[ ] M16 eye bolts (end termination anchors are eye bolts installed in a concrete slab)
[ ] tension load cell (mine is a 5 ton digital load cell)

The testing of knots is not as simple as one might at first think.

In fact, its a complex process - and it depends on what data you want to obtain and what theory you aim to prove or disprove.

Dan Lehman pointed out (long ago) that you need to invest time in creating carefully prepared test specimens - which involved weaving tiny cotton threads through the rope/cord and also creating a mirror image endless loop (so that you in fact test 2 knot specimens simultaneously). In tying a loop, you in fact need to apply double the force because a loop/sling of rope is stronger than a straight line piece of rope.

You need a load cell to measure the force applied and the peak force obtained.

You also need to carry out multiple tests to obtain a statistically valid sample of data.
Other factors to consider (different rope diameters, different types of rope, photos of knot specimens before and after testing, the list goes on and on...)

And all of this costs money and of course time.


Mark

[Dan_Lehman]

Dan Lehman pointed out (long ago) that you need to invest time
in creating carefully prepared test specimens - which involved weaving
tiny cotton threads through the rope/cord and also creating a mirror
image endless loop (so that you in fact test 2 knot specimens simultaneously).

The marker threads are not so tedious as we imagined
then --that going through the rope might be less
desirable (if different parts of the rope go different ways!)
than more simply threaded markers on surface strands.
Possibly, marker PENS can work as well.

And THiS is for learning something about the mechanisms
leading to breakage (or about slippage & compaction).

As for "mirror", rather, "matching" --esp. of equal handedness
if laid rope is used.  But having matching vs. mirrored knots
makes postmortem analysis easier, putting the two adjacent.

Finally, going for statistical purity I think is NOT something
to do in such limited-resources testing:
a. one likely won't have enough material (unless doing
some really small, cheap stuff --i.e., not with rope_;
b. the statistics are only so meaningful, anyway --with
questionable reach to other materials or even to others
tying the "same knot" in the same material!

At this stage of things, if one's got some limited resource
of cordage and time and ..., it's best I think to go for getting
good PHOTOS of before & after (& half-way there --"seriously"
loaded) states of the knot.  We'll learn a lot more from such
information than from a test report telling us that some
notion of a Knot-A tested somehow in something broke
at an average force of X.

(In the recent small-stuff testing we got an indication
that in at least that material the eyeknots --of several
types-- tested stronger than end-2-end knots, mostly.
For that, yes, we'll need some measure of force if going
to rope, and marker threads won't help.)

--dl*
====

[TMCD]

I will tinker around in my pole barn and see if I can devise a crude method for testing purposes but it clearly seems I don't have the finances or technological capabilities of doing these tests. It almost seems like it would take thousands of dollars to properly test knots and rope, especially heavier and stronger ropes.

[knot4u]

I will tinker around in my pole barn and see if I can devise a crude method for testing purposes but it clearly seems I don't have the finances or technological capabilities of doing these tests. It almost seems like it would take thousands of dollars to properly test knots and rope, especially heavier and stronger ropes.

Define "properly."  For my applications of rope and knots, expensive testing equipment is no more useful than the system I described above.  So, my tests are proper (although dangerous) for my purposes.  Likewise, Diff mentioned his choice of rope in his tests reflected the applications in which he uses knots.

[TMCD]

I was thinking along the lines of just a little more sophisticated system than the one you described Knot4U...that's not what I had in mind. I could easily tear drywall/joists out of the ceiling if I went to bouncing on rope at my size.

[Dan_Lehman]

I will tinker around in my pole barn and see if I can devise a crude method
for testing purposes but it clearly seems I don't have the finances or
technological capabilities of doing these tests. It almost seems like it
would take thousands of dollars to properly test knots and rope,
especially heavier and stronger ropes.

Much I've stated above, but let me remind you that some
folks have spent considerable $$$ on knots testing and yet
we don't know --I've not seen, anyway-- which side of a
sheet bend breaks, do we?  YOU might come up with some
initial answers on that (and J.P. could do the same quickly,
for comparison)!  Frankly, the lack of smarts going into some
of the testing that has been reported on is appalling : would
it occur to you to test both a "re-threaded(traced)" fig.8 eyeknot
AND one that was TIB (tied in the bight) ?!  --without any given
discrimination between the two (which could be a good research
project : i.e., to observe if the tying methods result in different
(-ly oriented) knots!

So, yes, if you were hoping to have some statistically significant
test data on calibrated strengths of several knots, you faced
quite some mountain of factors to overcome.  But, then, one
really needs to question the value of whatever results would
emerge?  Cordage use should stay so far clear of break strengths
that that attribute of a knot --if one could dare presume to
have indeed tied the **knot** that achieves that strength
(per material, per dressing/orientation)-- has little practical
value.  But, learning mechanisms of rupture, locations of it,
and so on, might go some way to raising understanding,
whose benefits should have promise.  (But let me catch myself
before I contradict prior words by suggesting that with such
insight we'll be able to make stronger knots!)   

You might be able to locate some place where two stout
trees provide all the anchor strength needed to do some
tests.


--dl*
====