In article , Spehro Pefhany
wrote:

On Mon, 25 Mar 2013 07:09:24 -0500, the renowned Karl Townsend
wrote:

Last year, I was air blast spraying the orchard, got out of position
when turning and caught the spayer head on a three inch tree branch.
Broke the head right off the machine. Imovable object meets
iresistable force.

OK, I've been rebuilding this for the last several days. I made the
mating surface from the air fan to the head two flat plates with eight
1/4" bolts holes around the outside of the duct. I want this to be the
weak spot this time. Steel, even grade 1, is too much, I guess.
Page 3042 of Mcmaster Carr has these plastic bolts
http://www.mcmaster.com/#catalog/119/3042/=m142xv

Could anybody give me an estmate of the relative strength of nylon,
polycarbonate, and PTFE, to grade 1 steel in 1/4" bolts? other
considerations on best shear bolts? Other material choices?

Karl


Brass maybe.

http://simple.wikipedia.org/wiki/Tensile_strength

McM have fiberglass/urethane that looks like it might be good
eg. 91345A684 if nylon isn't strong enough. Nylon is nasty hygroscopic
and I'd worry they might loosen up from expanding and shrinnking.

If you use metal you can always use smaller bolts.

You probably want something with a yield strength relatively close to
the ultimate strength for a clean break.

I'd be worried about nylon et al being too soft. How about aluminum?

Joe Gwinn