Author Topic: Knots for Homemade Pull-Up Bar  (Read 12440 times)

knot4u

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Knots for Homemade Pull-Up Bar
« on: July 27, 2010, 06:48:24 AM »
We have here a pull-up bar system.  The system includes ONE piece of rope, 8 steel anchors, 1 steel rod and ceiling studs.  The knots include 2 Slipped Buntline Hitches and 4 cow hitches.

I rate this system at over 1000 pounds max, but I will not test the limits to find out.  My 320-pound friend was able to swing on the bar without a problem.  By the way, because of the way the rope is tied, the bar does NOT swing and is surprisingly steady for all those who use it.  Each individual anchor is rated at 800 pounds (times 8 anchors).  The rope is rated at about 260 pounds.  The rod is a solid steel, weightlifting bar.  I have calculated the weak link to be the ceiling, but again I will not test the limits to find out.  The most difficult part was making the proper adjustments with a leveler.

WARNING: I am not responsible for any injuries suffered by any copiers!

Whole system:


Two Cow Hitches on one end of bar:


Opposite side of the two Cow Hitches in the pic above:


One of the two Slipped Buntline Hitches:
« Last Edit: July 27, 2010, 07:03:23 AM by knot4u »

SS369

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Re: Knots for Homemade Pull-Up Bar
« Reply #1 on: July 27, 2010, 01:22:34 PM »
Not sure, but it looks like the weak link is the rope. I have some just like it and don't trust it for anything important.
Nice setup though.

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roo

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Re: Knots for Homemade Pull-Up Bar
« Reply #2 on: July 27, 2010, 02:55:02 PM »
We have here a pull-up bar system.  The system includes ONE piece of rope, 8 steel anchors, 1 steel rod and ceiling studs.  The knots include 2 Slipped Buntline Hitches and 4 cow hitches.
Your system may be fine, but for reference, it's usually best to avoid reeving rope through eyebolts like that, as it causes a roughly 45 degree inward resultant force (down vector + sideways vector).
« Last Edit: July 27, 2010, 04:18:08 PM by roo »
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knot4u

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Re: Knots for Homemade Pull-Up Bar
« Reply #3 on: July 27, 2010, 03:34:11 PM »
OK everybody, please describe your improvement along with your critique.  I posted this system to see how others think I can improve it.  The last two posts are noted, but I don't readily understand what the recommended improvement is.  I'm relatively new to the study of knots and ropes.
« Last Edit: July 27, 2010, 03:41:14 PM by knot4u »

roo

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Re: Knots for Homemade Pull-Up Bar
« Reply #4 on: July 27, 2010, 04:14:29 PM »
OK everybody, please describe your improvement along with your critique.  
Like I said, your current system may withstand use just fine.  But since you asked, a single V on either end would probably work.  It'd involve two short pieces of rope, and the V shapes would lie in a plane perpendicular to the bar.

There would be your choice of crossing hitch at the base of each V.  The tops of each V would terminate with a hitch or loop of your choice at the anchors.

Slippery 8 Loops would make leveling very easy, assuming you choose a relatively simple crossing hitch (clove, constrictor).

http://notableknotindex.webs.com/slippery8.html
http://notableknotindex.webs.com/clovehitch.html
http://notableknotindex.webs.com/boaconstrictor.html
« Last Edit: July 27, 2010, 04:42:09 PM by roo »
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Dan_Lehman

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Re: Knots for Homemade Pull-Up Bar
« Reply #5 on: July 27, 2010, 06:08:28 PM »
I pretty much concur in Roo's observations.

In such systems as this, there are numerous solutions, any one of which
can be fine.  In this case, you might value having an un-cut length of
rope for something that you see as only semi-permanent, able
to be taken down (and re-set-up).

Scott remarks at the dubious reputation of this (oft'-called) "Home
Depot" rope -- is it multi-filament polypropylene?  (I have some
stuff like this, found here or there.)  But, then, you have EIGHT (-8-)
lines of support, so each needs only hold 125# for that half-ton load.
-- and you don't see actual loading getting to perhaps even a half
of this.  Safe Working Load for the rope is ... ?

The long reach parallel to the bar, along the ceiling, puts much
more material in the supports that feed that, and so those will
have more stretch and carry less load than the partner lines
whose reach is the short, perpendicular-to-bar direction.

One could eliminate all but one long reach by starting at one
point (as you do), going down to the bar, up to opposite
side and make a twin-eye knot (to connect to both bolts),
return to the bar, and up to the bolt beside the starting point,
tied off w/hitch, then reach to other end and do this structure
in reverse.  -- or all knots could be hitches (some tied in reverse
given working with the single rope).  This system could have
completely independent hitches to the bar (or not), giving
full redundancy if any line were cut.  (But what's the chance
of such failure?)  If your system has a cut, I think it still holds,
certainly for a while.

--dl*
====

knot4u

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Re: Knots for Homemade Pull-Up Bar
« Reply #6 on: July 28, 2010, 07:01:33 PM »
OK, I've been avoiding the Slippery 8, but I guess I'll have to try it out.  Also, there could be higher quality rope, but I really don't see the need.  The load on the rope is not coming anywhere close to the rated max.  (Do a quick F=ma analysis where the load on the bar is 1,000 pounds downward.)

That's a good point about the redundant failure safeguards (i.e., the multiple ropes instead of one rope).  However, as you guessed right, it's not really an issue in the current system.  It's highly unlikely that one leg will snap or be cut while I'm loading the pull-up bar.

I've decided to leave alone the present system because it's already over-engineered for my purposes.  However, I'll keep the ideas here in mind for future systems.
« Last Edit: July 28, 2010, 08:50:53 PM by knot4u »