On Jan 29, 2015, at 6:21 AM, David Nighswander  wrote:

> 3. Some time in the distant past a previous owner operator had grown tired of
replacing the shear pin and replaced it with a grade 8 bolt.
> Fortunately the driveshaft was light enough that it failed before the PTO
shaft did.

When I first went to work as an instructor for apprentices at the Boilermaker’s
Union, I saw a good sized metal lathe on the floor of the shop, but I never saw
it being used. I asked if it would be OK for me to use it to cut some test pipe
segments for my apprentices to weld. I was told that the lathe didn’t work. I
asked it it would be OK for me to look at it and see what was wrong.

They said, “Oh. it’s broken. Some one allowed the carriage to drive itself into
the spinning chuck, and something went, ‘SNAP!’ “ Yep, some real machinists.

 Aha, says I, the old millwright, the drive shear pin is broken on the drive. So
I opened it up and replaced the broken shear pin, and all was right with the
lathe again. And this was considered to be miraculous. Not everyone is trained
to know how machinery functions.