On 02/16/2015 2:24 PM, Danny D. wrote:
....

What we are thinking is that they sell these $100 treehouse attachment
bolts, designed specifically for trees (but they're expensive since
we'd use probably use four or six of them overall).
http://www.treehousesupplies.com/Tre...Bolts_s/41.htm

We can't find anything larger than one-inch wide bolts at our local
Home Depot, so, we have to order our bolts online, at any measure.

We're debating right now the feasibility of 1 inch or 2 inch bolts,
which are about twenty bucks each, versus the treehouse attachment
bolts which are five times as expensive.
....

That'd be cheap if it fails with somebody on it...

So, that's our next question. What kind of bolts make the most sense,
keeping cost in the equation (if cost were no object, the treehouse
bolts would do quite well).

There's bound to be a local Fastenal outfit nearby or similar but it's
not clear what you're comparing.

Those are a constant-diameter shank equivalent of a heavy-thread screw
in a hardened material supplied with an integral bolster. I see no
reason why one couldn't use any compatible compression sleeve; machining
that is undoubtedly a large component of the cost of these.

There's a link to an engineer's report at the site that says ultimate
capacity of these in shear is roughly 8500 lb in Doug fir; and Appendix
is referenced that compares material properties of other species
including redwood but it is, unfortunately not available. I'm quite
certain redwood will derate that performance by a pretty sizable chunk
but don't know a specific figure otomh.

Plus, again you need at _least_ a 2X (preferably imo 3X) safety factor.

I also noted the recommendation on one of these sites that before using
these to get a qualified arborist and engineer involved...methinks we've
been over that ploughed ground before that there's little heavy-lifting
on the engineering side going on first...

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