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Cable suspension
dwipoop 2007-05-28, 05:48 #1
since May 2007 · 2 posts
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Subject: Cable suspension
For extra support along with my posts I wanted to put in a cable support. I bought 1/4" or 1/2" steel cable. I think it was 1/4 with a wll of 1,400 lbs. Basically my tree is a split. So I was thinking I could use one cable to loop around one corner and wrap around the whole tree through 4 eyebolts(prevent rubbing against the tree) to the other corner.  However, I am not sure if that distributes my cables strength or doubles it. Also I am confused on what hardware to use. I was thinking maybe 1/2" or 3/4" eye bolts with length of like 6" and stuff. Also I wasn't sure how I would fasten the end of the cable that doesn't have a loop. And I wasn't able to find the stuff necessary(or what I thought necessary) to make another loop of the cable. I was planning on looping around the joist. The platforms dimension is 9' by 8'(I don't know why I choose that dimension). My treehouse finished with the roof and everything will be roughly 4,500 lbs with people in it. I was planning on doing a pitched roof so I didn't want the cable getting in the way.
The Treehouse Guide Administrator 2007-05-30, 17:46 #2
User title: The Treehouse Guide
since Aug 2006 · 67 posts
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Cables are generally used as a single length, looped at the ends through eyebolts and with a turnbuckle at one end (usually the top) to adjust the tension. The looped ends of the cable are secured with clamps. Hardware stores that stock steel cable will be able to show you the correct parts to put together the cable. All parts must be considered when determining the weight that can be supported, so a 1000lb eyebolt with 1500lb cable can only support 1000lb safely when used as per the manufacturer's instructions.

You should use only one eyebolt into the tree as the tree will eventually grow around the cable loop and could be badly damaged. Through bolts are the safest way to fit an eyebolt, but cause more damage than a lag style bolt. Eye bolts should be used with the bolt screwed in so that it follows the line of the cable where possible. Eye bolts with loads angled to one side will withstand much less load than rated (eg, a 45 degree angle reduces rating to just 25% of the original). In addition, eye bolts with loads at an angle should be of the type with a metal shoulder that will help resist any sideways force from crushing the tree or snapping the bolt.

Use a through bolt through the support beam to fix it to the cable. Again this should line up with the cable, so you need to drill the hole at an angle through the beam. This hole should run from top to bottom of the beam or, if this reduces the thickness of the beam too much, the cable could be fitted to a bracket around the beam.

(edited 13 July 09)
This post was edited on 2009-07-13, 15:17 by The Treehouse Guide.
dbarndt 2007-08-28, 23:58 #3
since Aug 2007 · 6 posts · Location: Hudson, MA, USA
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I have two decently large trunks - 36" and 30" diameters - that I want to secure eyebolt fasteners into in order to suspend cable from them to support my treehouse.  However, I have been unable to find lag eyebolts (with a screw-type end) rated strong enough (ex. 10000 lbs.) to more than hold the load.  Can "regular" (non-lag) eyebolts (that usually have nuts attached) that are rated high enough to support the load (and then some) be used somehow?  I don't think so.  But it's a Catch-22.  Any suggestions appreciated!
dbarndt 2007-08-30, 17:05 #4
since Aug 2007 · 6 posts · Location: Hudson, MA, USA
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Advice to self after more research:  Regular eye bolts are not safe for inserting into a tree without fully going through and out the other side.  You need to get lag eye bolts (screws).
joshuajon 2008-01-11, 15:45 #5
since Jan 2008 · 1 post
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Subject: Eyebolts at 90 degree angles?
I'm in the process of rigging a suspension cable for a new treehouse build and I'm unsure of how to attach the cable to my beams.  It seemed that an eyebolt would fit the bill but there's no way that I can think of to avoid attaching the cable at a 90 degree angle to the eyebolt.  Is it safe to assume that at 90 degrees on a shouldered eyebolt I will get 25% of the working load limit and simply need to look for 4 times the limit of my cable and turnbuckle?  For instance I have a 3/8" cable with a working load limit of 2200lbs.  Should a shouldered eyebolt attached at 90 degrees with a limit of 8800lbs be sufficient?  1" good enough?  Any thoughts appreciated.
amigabill 2008-01-16, 01:24 #6
since Jan 2008 · 1 post
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I'm thinking of making a treehouse, and would only use cable susensions to hold it up. We're still workign out how big it might be, and so don't have any particular weight goal yet, but don't know anything about calculating things to keep things reliable and safe. I'd kind of like to have any support cables attached to tree branches to come together to a strong metal plate, and have other cables go from this plate down to attachment points in the treehouse. It'd kindof be likie a giant christmas tree ornament hanging there. And then have some other cables off the side of the house to help hold it somewhat in place so it doesn't end up swinging around in a strong wind, which could be a bad thing.

This idea came up to basically have no real walls. This top plate would distribute lift support to the roof and floor via cabling around the perimiter, and then have a tarp covering it, sort of more like a tent than a house I guess, with some safety railing or something so you don't fall out by accident.

When using eyebolts into steel plate, do I have them so the bolt part is angled/perpendicular to the cable line, or in-line with the thread/nut end 180degrees pointing away from the cable line? I assume I'll be using shouldered eyes exclusively.

For a cable-suspended floor, what sort of framing should I consider? Wood joists (2x8 or 2x10 under the plywood?), some steel framework instead of wood joists to get a better strength/weight ratio, or what?

How might one calculate appropriate steel plate thickness, diameter, etc. to ensure safe strength for all the forces involved with the cable distribution?

Is there example math or rules of thumb for making sure enough cables are used for the given weight, particularly if things are not at perfect 90 or 180 degree angles, should we do an uncovered balcony area making the floor larger than the roof area?

If we run a cable out to a pulley and back to help with raising the treehouse into place, do we then have a support twice as strong as a single piece of cable, or is it still the same strength as a single length of that cable?

But I don't know if what I'm thinking is practical or safe or sane or anything. Any thoughts, advice, comments, pointers to math or other information abotu these sorts of cable questions, safety thoughts, etc. are all greatly appreciated.
RainCaster 2008-01-18, 17:14 #7
since Sep 2007 · 5 posts · Location: Rural Washington (state)
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Subject: I suspended one corner
I have three corners of the platform supported by normal flex joints into trees, but the fourth corner hangs out in free air, so it is suspended by a large cable. I may have over-rigged this slightly, but it is my children's safety  I'm concerned about...

One of my passions is sailing, so I designed the rigging exactly like the rig holding up a sailboat mast. At the top is a 1 inch bolt that I thread directly into the tree with a 15/16 ship's bore bit. The bolt has two tang plates attached to it, and then the top eye fitting for the cable attaches to the tang plates with a 5/8 inch SS clevice pin. The cable is 3/8 SS, rated for 17,000 breaking strength. The bottom fitting is a SS turnbuckle and fork fitting, which attaches to a custom welded bracket with another clevice pin. One photo of the bottom can be found on my treehouse page (http://www.illuminosi.com/treehouse.htm)  The rigging bits I collected from combination of places. There are no bends in the cable as that will greatly weaken it. No cable clamps or eyebolts either. Many of the materials can be had at http://www.riggingonly.com, and there are a number of pictures there to explain how the hardware works.
gagliardones 2009-07-10, 17:19 #8
since Jul 2009 · 1 post
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In reply to post #2
I'm very confused about the use of eye bolts.  In your guide you wrote that "the eye bolt must enter at a right angle to the cable", but in your response here you write that "Eye bolts should be used with the bolt screwed in so that it follows the line of the cable. Eye bolts with loads angled to one side will withstand much less load than rated."  Is this saying the same thing and I am just understanding it wrong?

2 Other question that I am grappling with:

1.  If I use a through eye bolt (instead of a lag) will the extra damage it caused weaken (compartmentalize) the tree and make it MORE unsafe that if I used a lag eye bolt?  I can't find thick enough lag eye bolts that have shoulders-  They are all the wire type (not forged) and are light duty- even at bolt depot.

2.  In your diagram for a 2 tree design you have 2 eye bolts positioned at each tree.  How do you afix these and avoid compartmentalization. Do I put them 2 feet apart vertically? If I do that is it wise to drill through the tree?  Thanks for your consideration. Steve
The Treehouse Guide Administrator 2009-07-13, 15:14 #9
User title: The Treehouse Guide
since Aug 2006 · 67 posts
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@gargliadones:
I think this information on eye bolts/screws needs to be re-worded, as what I've written is contradictory.

Eye bolts and screws are rated on a safe working load (SWL) pulling in line with the bolt. If the load is angled, the SWL will be reduced by a large amount. Sometimes this is listed in the specifications, sometimes not. When fitting a bolt in a tree it is highly likely that you will be loading the eye at an angle of 45-60 degrees so you will have to overspecify the size of the bolt accordingly.

In terms of tree damage, there is very little data about what will or will not damage the tree. The advice to reduce the number of puncture points is based on the hypothesis that having more than one puncture point close together will cause the tree to seal off the area around and between the bolts, possibly causing decay and future failure of the joint. In terms of fitting an eye bolt, I would suggest that bolting through the tree is safer in the short term, as a bolt with nut and washer is less likely to pull out than a lag screw. This does mean that you are making a puncture wound on each side of the tree, but the tree should be able to seal these wounds up without joining them and without causing significant disruption to nutrient/water flow.

For major supports where the parts will be carrying a lot of weight, I would recommend getting a design made up by one of the treehouse building companies as your situation may require a specially engineered solution. Otherwise you may be better trying to support the treehouse from underneath with knee braces or posts.
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