Introduction: Treehouse Hardware Series - Tree Attachment Bolt (TAB)
Treehouse ambitions still lingering since childhood? Not sure where or how to put that dream into action?
Look no further! I promise by the end of this instructable you will be fully learn-ed on one of the central unknowns in the world of treehouse building, how to properly attach a treehouse to a tree without barraging a box of your Dad's 12 penny nails into the trunk.
Drill Forstner Hole - Bushing
Drill Auger Hole - Theads
Build Structure on TAB
Links Alternative Methods
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Step 1: Tree Health - Links
It would be impossible to cover even a portion of the tree health category sufficiently so I've provided a number of helpful links below to get your research . If you plan to invest quite a bit of money and time into your treehouse project I recommend contacting a local arborist as they will be most up to date and knowledgeable on local species, blights, harmful fungus, pests, and characteristics of the specific species for a specific region.
Tree Health links:
Live in CA? Have an Oak? Take a look at this first!
Tree Diseases to be aware of.
Step 2: Tools
Tools you will need include:
High Torque ( geared down drill ) - I prefer the Milwaukee brand Hole Hog Model
Auger Drill Bit ( appropriately sized to fit your tree bolt )
http://www.portlandbolt.com/technicalinformation/l... (use this link to understand the diameter of the pilot hole needed)
Self Feed Forstner Bit - I use also Milwaukee brand as they make them in all sizes
Burly 3/4" drive ratchet & breaker bar ( breaker bar is a essentially any tube that will slide over the handle of your ratchet )
Appropriately sized socket for your nut size/ all-thread size
Sharp pocket knife/razor blade
Straw ( used to blow out debris from the tree hole )
Step 3: Hardware
Tree Bolts or as they are referred to in the industry TAB ( Tree Attachment Bolts ) come in all shapes and sizes. They are based on a basic premise that load should be distributed into greater surface area at the moment or location where the bolt exits the tree.
The TAB consists of a boss or giant bushing affixed at the end of a bolt. Depending upon the context in which you plan to use the bolt you may have additional steel bar extending past the bushing on the outside of the tree. If you plan to use the TAB as a rigging point only then your bar needs to extend only a few inches past the pushing on the outside of the tree. I've pictured both types above.
Also pictured is a bracket that slips over the protruding end of the TAB. I call this a Bolt Hook. It is a simple laser cut bracket of 3/8" mild steel with a bit of a kink in it half way through. This hook is either used to rig directly off or can be used to rig a support cable that triangulates the cantilevered end of the TAB extension ( pictured ).
Here are a few resources for purchasing your tree hardware:
Step 4: Bolt Locations
Now that all of the tools and proper hardware are gathered. It is now time to design the treehouse structure. I will not cover this process in this Instructable but will give you a few links to get started.
Brief on the Engineering
The tree connections need to be able to support the worst case loading scenario that could take place in the treehouse. I usually describe this as fully loaded to the Live Load Capacity, in an earth quake wind storm in the winter during a dance party.
This means that the total capacity of your connection points (if load and center of mass is distributed evenly) should be have a 5X safety factor. This means the capacity of your connections is 5 times greater than the total weight of the structure + the total weight of the people in the structure. Many of the tree bolts come with ratings. Since your installing this structure in a tree it is best to over engineer. My rule of thumb when rigging a structure with cabling is to base the capability of the structure on 3 rigging points although there are always more than 3 points distributing the load. This is to ensure that in a windy scenario should the structure swing onto only 3 points it is capable.
Here are a few websites that will guide your engineering process if you will be performing any load simulations. Select your wood type and discover its properties so you can discover accurate results in your simulation.
The best one is www.matweb.com.
Enter the type of wood in the Text Search option in the middle of the page - try Oak and you'll see a bunch of options. Here are two links to a couple of the Oaks for example.. but generally pretty good cause they list for different moisture content, grain direction, etc.
Here's another one. A good long list of species, though not quite as much data on each one as MatWeb.
Step 5: Drill Forstner Hole- Bushing
If the Treehouse will be resting on the TABs then it will most likely be necessary that the two bolts protrusions are directly parallel and level to each other. This requires extreme accuracy in locating the hole heights and the drilling of the holes to ensure a level resting platform for the beams.
#1 - A water level consists of a bendable clear tube filled with water. This simple tool will provide the ability to mark two hole locations on the tree either side of the tree or on two or more trees. Eyeing the water level on each side of the tube after waiting for the water to settle mark each hole location with a nail.
#2 - Install the Forstner Bit into the drill. Pull out the nail that was marking the location. Drill the depth of the hole shallow enough to ensure that the Boss on the TAB will protrude out of the tree enough to seal off any portion of the exposed interior of the tree. This is to ensure there is no space for infection or bugs to easily enter into and disturbe the critical nutrient flow layers just under the bark of the tree.
Step 6: Drill Auger Hole - Threads
#1 - (Leveling drill holes to each other is only necessary when installing TABs where the beam will be seated resting directly on the TAB.)
Attach the Auger drill bit in the drill. Using a Torpedo Level and a friend or two to check your drill trajectory for accuracy begin drilling the hole for the TAB threads. Accurately locate the center pin hole left behind from the Forstner bit with the tip of the Auger bit. Raise drill to a level position using the Torpedo Level directly on the Auger drill bit. Also make sure that your horizontal trajectory is to the angle you wish. Begin drilling, use a friend who can keep an eye on your drill bit as you drill to ensure it stays level. Check often using the Torpedo Level during this process as well until the Auger is to deep. There are ways to create jigs specific to your drill to ensure that your drill trajectory is perfectly level as you plunge the drill into the tree. Many professionals use rigs like this during this process to ensure accuracy.
Once the hole is completed use a long straw to blow all of the wood chip debris from out of the hole. This will ensure a smoother installation of the bolt.
Step 7: Attach TABs
Screwing the TAB can be an aerobic activity so make sure you have your money makers on.
#1 - Insert the back end of the TAB into the hole. Screw a nut onto the other end of the TAB. Use a hammer to knock the first couple threads in into the hole.
#2 - Hold the TAB level and start turning the bolt into the tree very slowly to ensure the first couple of threads catch the wood.
#3 - Continue screwing until the bolt is in the tree. It will probably become quite difficult once the bushing is up against the hole, at this point use the breaker bar ratchet handle extension to turn the bolt in the rest of the way.
* IMPORTANT - As the tree is a giant vascular system that pulls nutrients in water to its upper branches, there exists a small amount of pressure in the tree. This preassure causes the interior of the hole in the tree to swell a bit which starts immediately after drilling. Make sure to install the bolt directly after drilling the hole. There is about a two hour window to install the bolt, after this it will become progressively more difficult.
Step 8: Build Structure on TAB
Once all of the bolts are completely installed, let the building begin! I've included two pictures which display different ways to triangulate the cantilevered end of your TAB should you be significantly loading the TAB. One of them reinforces the beam form the tip of the TAB and the other near the center with the beam loaded on the tip.
As my tabs are created from simple 1.25" all thread and a 4145 laithed bushing I needed to sheeth the treads where the beam would rest against the TAB all thread. I choose to do this because my bolting system allows for moement between the two bolts and there for the trees. The sheath that I used is a piece of pipe who's interior dimension ( ID ) matches nearly perfectly the outer dimension ( OD ) of my all thread. This sleeve sheath will protect the beam from digging into the all thread and allow for less friction in the system.
I was able to make this system dynamic and movable by fixing only one side of my beam to the bolt. This is illustrated in the pictures by the triangle plates. One plate has two holes where I've affixed the plate with bolts. The other side of the beam has a similar plate only on this side the plate has a long slot shaped hole. This long slot hole will allow this side of the beam to slide along the TAB and there fore allowing for movement in the system when the trees sway in the breeze.
Step 9: Links and Alternative Methods