Z-Rig ???

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If you do a Google search on "Z rig" you'll find lots of information on search and rescue pages. It's a basic MA setup.

The setup that Sherrill sells is a piggy back 4:1 or 5:1 depending on which way you rig.

A Z rig is made with the pull rope a piggy back is an MA system that is added onto the pull line.

Tom
 
You can tighten a speed line with a Z rig (3:1) or a 5:1 etc. The picture i have of Sherrills speedline pictures a Zrig to tighten the line. They sell a nice 5:1 rig for pretightening lines. Also a mini traxion for a pretightening and hold in a Zrig. You can pretighten, and the traxion can hold the tension on, while you reset to impact it tighter etc. They also sell neat fiddle blocks that help maximize the power by taking out friction between the legs, one of these also has a cam for holding tension.

Power is power, it can be used for many things, also re-arrainged. The pattern of pull on a load and the friction points/bends determines the power potential. Placing these patterns for pulling, lifting, pretightening, lowering etc. can give great flexability from a simple principle, as long as you can keep redirecting a given force to pull again on the work, the work will be easier, but take more line/time to achieve! For these flexible levers just allow you to funnel more power into a smaller distance than produced it! Like a gearbox, ramp, lever etc. This can even be done with brakeforce in lowering, brake force can be increased with these rigs, for brake force is a force; but you only realize that it is a force or what it has to offer, until it is acted upon by push/pull of something else, but as a force, it can be increased with one of these rigs.
 
Be careful if you use a camming device (Wall Hauler, Pro or Mini Traxion, Gibbs etc.) in a mechanical advantage system. They can shred or sever a rope. I am not saying that you should never use a cam, but you need to be aware of the forces generated at different parts of the rig before you incorporate such a device into the system. Friction hitches are generally safer and the cords are cheap and readily available.

Mahk
 
I made and used a Z rig today to fell a 30' tall, 24" Hickory trunk that had a severe lean over the back fence. There was a good size Live Oak about 100' away directly opposite the lean of the 30' Hickory trunk so I tied a 150' line to the top of the trunk and set a Z rig off the Live Oak. I also had another tag line to the top of the trunk to pull it over. Tightening the 3-1 Z with light pressure from my truck helped compensate for the lean so I was able to notch and fell the trunk parallel with the back fence.

I estimate that I had 500-600 lbs of pull with the truck so that equated to 1500-1800 lbs of pull on the top of the spar. I dropped the tree at about a 80*-85* angle to that line. I used a homemade 1/2" rope prussik and steel biner to attach the pulley to the line and a 3/4" Tenex sling with steel biner to attach the other pulley to the oak.
 
Originally posted by Mike Maas
What kind of pulleys did you use?
What prussic did you use, and at what force do you think the prussic would slip?

Stainless CMI pulleys from Sherrill.
I used a triple prussik made from 1/2" Safety Blue and a 51Kn steel biner.
I was using steady pressure, not shock loading. With the triple prussik I wasn't worried about slippage. I have no proof, but I believe the rope would have separated or otherwise failed before the prussik slipped. I try not to test my equipment to the point of failure.
 
A word of caution. Be sure to size all of the components in any MA system correctly.

The best source of MA procedures for working ropes is the search and rescue profession. They have tested many combinations of ropes and hitches.

In most S&R setups they require doubled, triple-wrap prusiks. The sizes of the rope/cord are pretty well standardized too.

Mahk gave good advice. I've seen test results where cams have damaged ropes from man-hauling ropes. It seems evident that the lever of a camming device amplifies the input load. Work out the MS there too.

Tom
 
I use a Z-rig on nearly every tree I put a line on to pull over. It only takes a couple of minutes to set up and even though the tree may be pulled over by hand, I like the ease and extra security of mech. advantage. I use CMI stainless pulleys, steel biners, and 8mm cord for the triple wrapped prusiks. If I want to capture my tension I'll use a prusik minding pulley at the anchor with tandem triple wrapped prusiks. It's amazing the power you can generate with the leverage of a high tie point on a tree.
 
The cam advice of Mahk & Tom is very good especially when the mechanical rope grab is positioned on a host line and a 5x1 compression gig is hooked up to it, especially impacted by bodyweight or more than one man. In this position, at 200#+ input to the 5x1 the cam device digs 1000#+ into the host line it is tightening.

The position i outlined was as a one way brake for the control leg of a 3x1 in a ZRig. In this position, the device only digs in the line at 200# with 200# pull. Another diffrence is in this position the device clamps tight in between pulls, instead of during your pulls. i find the mini-traxion very handy for this. It can hold tension while you do something else, take a break, or hold tension so you don't have to and can use all your force to impact the line. Rather than having to use a part of your potential force to hold the tension in a system your self, and the rest to impact the line tighter, with the device you can throw all your potential force into impacting the line tighter. Also good for sweating in. So in this configuration the cam tightens to take the tension of a single leg atr rest, rather than the force of compounding and impacting of 5 pulls of force.
 
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There's a nice article called "Understanding Mechanical Advantage" in the Fall 2002 issue
of "Western Arborist", the magazine of the Western Chapter of the ISA. "Understanding Mechanical Advantage" was written by
Peter S. Donzelli, Ken Palmer, Rip Tompkins and Stanley Longstaff.

la02fall-07.jpg


Photos and diagrams show the z-rig in action. Here's a shot of the in-line dynamometers measuring the forces involved.
 
Originally posted by TheTreeSpyder
.

The position i outlined was as a one way brake for the control leg of a 3x1 in a ZRig. In this position, the device only digs in the line at 200# with 200# pull. Another diffrence is in this position the device clamps tight in between pulls, instead of during your pulls.


It depends where and how you position the traxion. Assuming a 3:1 system rigged to advantage, when you pull with 200# you can generate 600# of output force. If the traxion is positioned so that when you let go there are only two parts of line still under tension then that 600# of output force is now being held by and disributed between only two lines. Thus each of those lines (one of which has the traxion on it) now holds 300#. Worse, if the traxion is positioned as the anchor pulley, then when you let go there is only one line that captures and holds the output force so the traxion now bears the total 600# of output force.

It is important to look at how many parts of line are still under tension after you let go of the line you are pulling. The total generated force is then shared only by these lines. This is true whether you use a camming device or knots to capture the line pull.

Mahk
 
Originally posted by Oxman

There's a nice article called "Understanding Mechanical Advantage" in the Fall 2002 issue
of "Western Arborist", the magazine of the Western Chapter of the ISA. "Understanding Mechanical Advantage" was written by
Peter S. Donzelli, Ken Palmer, Rip Tompkins and Stanley Longstaff.


For those who don't live on the west coast, this article also appeared in the June 1998 issue of Arborist News magazine. It is scheduled to be included in a compendia of CEU articles that the ISA plans to publish this summer.

Mahk
 
Wow Mahk, i see that now thanks! i try to catch all of those myself, but gotta respect you catching something on something i've combed over!

i see that all the forces are self contained in that setup when released, instead of relying on an anchor for the control line to pull from, dividing the load on the cam further. i just assumed that the 3:1 still had 3 legs of support, instead of the 2 as in a prussik/knottender ararringement similarily placed, but gripping the line on the other side of the device; but the real point is the loss of the supporting anchor for the control line.

Very good point, though i still will use it in the position of non impact on ZRig, i will do so more judiciously as you point out it would carry 1/2 the load of tightened line (instead of 1/3) , non-impacting line in a 3:1. That still is safer than a 5x impacted line in a 5:1 force on the cam device.
 
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