On Apr 12, 1:01*am, RS at work wrote:
I am thinking about making a blade adaptor for my lawn mower that has
a sacrificial shear pin so when I am out mowing down the tall weeds
and find that chunk of concrete or stump that someone tossed into the
field it will reduce the stress on the mower engine.

On my mower with a Tecumseh 195cc motor, I have had to replace the
flywheel as the shaft is steel and the spline key is steel but the
flywheel itself is cast aluminum. *Although I found a new one on e-bay
for $30 if I had to get one from a dealer it would have run $60 or so,
and added to the cost of a new blade ($10-20) and a new blade adaptor
this gets really pricey.

My design is about the same as the factory set up except the torque
will be transmitted through the shear pin(s).

My question is how to size the pin or pins? *I want them to be the
weakest link, but to hold up when mowing down the big nasty weeds.

My gut feeling says that two 3/16 brass pins ought to do the trick,
but I figured that some one here might have some experience with this
kind of calculation.

Roger Shoaf

Some thoughts from someone who has never had to engineer a pin, but is
pretty good at breaking them:

A bit more work, but slightly oversize with grooves where it should
shear I think leads to better 'quick release' action, and helps keep
the pin from smearing into the gap between the parts (making
disassembly difficult, and perhaps even making the parts 're-grab').

Brass might be too malleable (and prone to smearing upon breakage),
depends I'd think on if the part is loose except for the pins or if
there is no movement between the parts until the pin breaks.


Dave