Bending moment question

[Neill]

So I cut a fairly wide mouth. It allows the butt to slide off and down instead of the butt pushing off or jumping off the base of the cut when the hinge breaks. Tends to not push the spar back away from the mouth when the hinge is breaking. Also less tendency to go tips down so fast as was mentioned above. It just pushes back a little and slides off instead of jumping off the cut and speeding up the rotation. Make sense?

Makes sense, thank you for taking the time to explain

 

[Neill]

I’m assuming this thread is in the interest of minimizing pushback, therefore minimizing the “ride”? I agree about the humbolt face, and I may add (when situations allow/by experts only) that severing hingewood on both sides (shortening the length of hinge) also helps in reducing the pushback/bending moment. To be clear if the diameter of trunk at hinge is 15” across you’d shave an inch or two an each side leaving 10-12” long hinge inside. Also leaving some brush on the spar (if allowable) helps with dampening that “lashing” effect.

Minimizing the ride yes, but also in the interest of working above weaknesses. I can see where brush would be a benefit in reducing the speed of a falling top- if it’s vertical. A leaning top with extra brush would add leverage right?

 

[Neill]

The arborpod video brought up something interesting I haven't thought about before. When it said that the greatest pushback force is when the top is at 45 degrees and if the hinge breaks right at this moment it would result in more reaction forces.

I've always thought that you'll have more of a ride if the hinge is still attached when the piece is almost horizontal.

There was also an ISA book I read that said a 70 degree face cut for a top is ideal....

Now I'm confused....

I’m glad it’s not just me. My coworker and I had this discussion too. We were in two different camps. that helped prompt this thread.

 

[Chris Schultz]

Minimizing the ride yes, but also in the interest of working above weaknesses. I can see where brush would be a benefit in reducing the speed of a falling top- if it’s vertical. A leaning top with extra brush would add leverage right?

Nothing we do is in a “perfect vacuum” and each situation is going to be different…. I think working above a defect is a perfect example of where I’d want to minimize “the ride”. Some trees have defects I’d also want to minimize the weight on or above…… give and take here.