Instructables

Step 6: Build the platform

Picture of Build the platform
IMG_0435.JPG

Using 3" deck screws, attach the four 2 x 6's perpendicularly to one of the other 2 x 6's. Make sure they're spaced so that when you put it up in the tree, the perpendicular joists will miss the tree! With someone's help, put the contraption up in the tree, center it, and tie it down.

Screw the other 2 x 6 to the other end of the platform, and check that it is centered and square. For squareness, measure the diagonals and ensure they are the same.

 
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More bolts, in slots, please.
Three per tree in each board are recommended.
Two would be better than what you have.
The problem with your application is that the trees in high winds can exert a HUGE horizontal torque force on the bolt heads that could bend, tear out, or shear them.
What we did in our very similar situation was to drill several holes (just a bit bigger than the bolt diameter) next to each other in the boards.
ooo
Then we chiseled them out into slots.
(___)
Then added a bolt with a BIG washer in the middle of each slot.
(_O_)
This design allows the trees to move in high winds independent of each other without snapping or bending the bolts.
Also the bolts should NOT be tightened. The washers should be able to rotate. This allows the bolts to move side to side in high winds, and for the whole structure to "give" a little.
If you think of the tree as a huge lever, and the distance the wind can move it both ways, you start to understand the amazing forces at work here.
We love your treehouse.
Come to think of it, we love all of them.
Werner1114 years ago
I would have added another bolt in for each tree, but it looks good :)