Author Topic: Best type of string for outdoor use if under constant tension?  (Read 8902 times)

Korg

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Best type of string for outdoor use if under constant tension?
« on: February 20, 2012, 08:58:39 PM »
Hey all,

I have a yard that I'm measuring out into a grid.  I have stakes hammered into the corners and some vertices of the grid.  I connect some together with string. 

I need a type of string that can stay as straight as possible once made taught between stakes for as long as possible, without unduly stretching into saggy catenaries.

I had used jute at first for lack of better rope around.  That soon became wet and heavy.  I've just put up some kite string; I don't know what material it is but its lightness is helpful. 

The furthest distance I span is 8 metres.

What would you recommend?

roo

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Re: Best type of string for outdoor use if under constant tension?
« Reply #1 on: February 20, 2012, 09:07:30 PM »
Mason line is commonly used for such purposes and is available at just about any hardware store.

http://tinyurl.com/723ozfn

« Last Edit: February 20, 2012, 09:08:18 PM by roo »
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Korg

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Re: Best type of string for outdoor use if under constant tension?
« Reply #2 on: February 20, 2012, 09:27:35 PM »
Thanks.

Dan_Lehman

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Re: Best type of string for outdoor use if under constant tension?
« Reply #3 on: February 21, 2012, 07:12:53 AM »
As Roo says.  Although from a material & construction
viewpoint, one might doubt some of this as meeting
the task --the most stretchy material (nylon), laid (twisted)!
Some mason line is braided.
But it should work, and is available in a variety of bright
colors, which might help (either in variety, or brightness).
(Some pre-stretched polyester is what would be expected!)

If sagging is yet a real problem even with this line,
you might endeavor to set it up with some means
of putting in additional tension, periodically --some
sort of small stick (or --more uniform-- nail) around
which one can turn some line (or tie off with e.g. the
tautline hitch which can be adjusted).


--dl*
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knot4u

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Re: Best type of string for outdoor use if under constant tension?
« Reply #4 on: February 21, 2012, 08:35:32 PM »
I would think spring in the line is what you'd want here. Otherwise, without the spring, any loss in tension would cause a sag in the line, right? For example, jute twine has almost zero spring (not good here).
« Last Edit: February 21, 2012, 08:37:53 PM by knot4u »

roo

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Re: Best type of string for outdoor use if under constant tension?
« Reply #5 on: February 21, 2012, 09:27:39 PM »
I would think spring in the line is what you'd want here. Otherwise, without the spring, any loss in tension would cause a sag in the line, right? For example, jute twine has almost zero spring (not good here).
http://www.spaceagecontrol.com/calccabl.htm

A catenary shape depends on tension, weight, and anchor separation.  Tension in a highly inelastic material will react severely to any change in length.   Tension in a highly elastic material will not respond as much to change in length.

Hence you can reel in slack in a highly elastic material all day (so to speak), and not see much improvement in tension or catenary sag, although you'll eventually get there.  Conversely, you can let out elastic material into a catenary and not see as much sag increase and tension degradation compared to an inelastic material.

The ideal material would be elastic, light, and have a high tensile strength that would allow you to dump lots of tension in.  Nylon is a decent fit.

On the other hand, added weight from rain would not be counteracted by a large tension rise in more elastic material.  So a rain-shedding coating could be good addition, so long as that doesn't add too much weight (and cost). 

« Last Edit: February 24, 2012, 06:29:05 PM by roo »
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Dan_Lehman

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Re: Best type of string for outdoor use if under constant tension?
« Reply #6 on: February 24, 2012, 01:34:14 AM »
I would think spring in the line is what you'd want here. Otherwise, without the spring, any loss in tension would cause a sag in the line, right? For example, jute twine has almost zero spring (not good here).

Ya, this makes sense --you pull tight, straight,
and then MORE (no straighter, but now with extra
tension which can be yielded w/o sagging).  I was
thinking of some notion of "creep", I guess.  Anyway,
masons do use mason line and hope for straightness!
(nice colors for whipping, also)

 :)
« Last Edit: February 26, 2012, 04:34:24 AM by Dan_Lehman »