On Fri, 16 Jan 2004 09:11:16 -0500, Terry King
wrote:

Thanks for this:
Shear is directly proportional to the area. a 5/16" bolt would be
1.55 times more shear strength. Drilling it out to a clean hole
would also eliminate some unknown amount of bending that is going
on.

The grade 5 and grade 8 bolts would have more shear strength than
the usual soft steel but they would be much harder than the shaft
and tube so you would mangle them before the bolt sheared, NOT
what you want.
OK, Won't do that!


Generally a Grade 2 bolt is what you want for a shear pin, with a snug
fit. Which reminds me, I better pick up a couple sets for the old Noma
as I used the last set when I serviced it this fall.
And, this comment:
If the shear holes are getting battered, then perhaps it is the
movement that is contributing to the shear. Maybe new holes drilled
ninety degrees out of line of the old holes and some distance away?

OK, here's what I think I'll do (Comments and GotYas appreciated):

1. Drill existing holes out to 5/16". Temporarily install 5/16 Capscews
(smooth shank). This should stabilize the current rotational 'slop'.

2. Drill new 1/4" holes in the stabilized tube and bar, an inch or so
away and 90 degrees to the original holes. Install 1/4" mild steel
capscrews.

3. Remove 5/16 capscrews, run for a while.

4. If problem continues a lot, use the 5/16" (1.5 times the shear torque)
mild steel capscrews.

I have 800 feet of dirt road to blow, and although I walk the path in the
Fall and throw a lot of stuff off, I always seem to miss the odd piece of
fallen branch, rock etc. So I understand that I'm in a difficult
environment.

Meanwhile, my Grandkids are coming this weekend, and we've got a dynamite
sliding hill with no traffic except the occasional snowmobile...

Thanks for the help in understanding this!