hinge failure, Spydie, help!!

[Matt Follett]

This goes out to Treespyder, and all the other hinge freaks.

Yesterday was an incredible day...until the end... So I'll start with the beginning.

We we're sub working for another local company who was 'too backed up' so on and so forth, we spent most of the week dead wooding and cleaning a bunch of mature trees on a slope overlooking 'The Lake' (Ontario). selectivley removing a few Norway maples (all) and leaving the Oaks, Ironwood and Sweet Birch (Betual Lenta!!!! bigger then I've ever seen) Then we moved into a couple big removals, a massive spruce which I felt bad doing but the homeower was doing major renovations/addition /foundation work which would undermine the tree, so...
Then we took down red oak and a Sugar Maple to open up a view over the water from the house, this is where the hinge work got interesting, we pulled all of them from WAY over center back up and onto the bank, (5:1 tackle, and 3 people) it was an impressive site to watch them lift up and over center, I should have got pics...

But then all H#$% broke lose, end of the day and this 3/4 dead sweet cherry needed felling, up the bank as well, we did the same trick, set the line, anchor, block etc. I got to the base of the tree, and realized it was quite hollow, about 20-25" across and probably a 10 inch clear cavity... Tree was in marginal health so I assumed some clear sap wood would be there (opps) (notice I said 3/4 dead above, I'm trying to CMA ) anyway pretty much a static straight up, a bit of a side lead, but we had set the pull line just off center of the intended drop to help compensate...
Notch in, okay happy with the appearance... start the back cut, everything smooth, get to 6" holding wood tree starts to move from the pre tension, (oh hurry get to the hinge!) at 4" I decide it's on it's way and let the team pull, everything is fine, tree hits 60 degrees BAM!!!!!!! swings and drops 30 degrees off line, hits the slope sidways and slides to 45 degrees of line, Many @#$% #$%@#$ @#$#$% uttered by me and confusion sets in the air, what just happened???

Nobody got hurt, nothing was damaged (except my ego) but I still cant figure it out the notch was clean, the back cut was straight etc etc, I wish I had pics but I will do my best to decribe the forensics, very little clear sap wood 1-2" with then 2-3 inches of moderate discoloured/decayed heartwood then cavity, the hinge wood on the left (the tree went right) side shows little compression on the face, and then tension force, which show where it pulled away and broke free, but... the right side shows more typical compression at the face and tension further back...

It's almost as if the left hinge failed early, and the right kept going, thed sombody out and kicked the top the other way.

I guess the thing that concerns me is this is the third time a felling hinge has gone wrong, beyond 'oops, oh well' the other two were early in my career and both times I over cut the hinge cause I didn't watch /know better... I though I had passed reckless foolishness, and had things pretty much under control.
It's an eye opener again, We rarely fell big full tops near targets, I guess this tells me why. I've done lots of hollow stems in the past, sometime with a bit of a side lead and so forth, UM, just still mad at myself....

 

[TheTreeSpyder]

Glad everyone is alright, hard to 2nd, blind guess someone fairly..... But, i do like the exercise your situation offers for exploring thanx! Obviously to get that far, that day, ya where doin' somehting write.....


First, let me be real wimpy and jest say that bringing stuff front to back is tricky, and decaying etc. stuff is tricky; and both multiplied together..... Especially when 1 componenet demands more and more flexability at higher levels of difficulty and position; as the other likewise reliquishes less and less of that need as it raises difficulty(decay)... Not real familiar with wood type, and 'brittleness' in good health let alone decline. i think kiln dried wood can be stronger/ less flexible as trade, so even look at strong but drier/deader stuff as perhaps even stronger but less flexible/ shock worthy.

It must fall where the balances of pull/push say; if pulled right must have released, pushed or pulled right. If C.o.B. is to R., then compressed hinge fiber would be on right, not left. The compressed pivot fibers would only be on both sides for balanced load side to side with axis of hinge.

Back to front does a few things we usually don't face, like the hinge starts out stretched on the pull side, then compressed as back does opposite. Also, as the tree comes up to the stump, the leveraged load is decreasing, then increasing as it tilts towards rig, easy to take too much hinge and that to carry you thru decreasing leveraged load on hinge of from back lean to standing straight (at ~no hinge load).

Sometimes, i can curl the head of a fall a lil to the R around another tree top, then to the L under the other tree top to land. i use the pull in the hinge for stage 1 to pull to the R. The pushes in the face i call phase 2 to push from R(where i was pulling force to, so i use that force), to sweep slightly L. All within the gunned focal of the hinge (wider across hinge has more adjustment within focal than a narrow hinge). So along with Stumper's analasis of wider hinge having more flexability, we once again see more side to side adjustment available.

So generally i think/plan in terms of the 2 stages: pull in the hinge, then later pushes in the faces. So, a lot of times, for problems later in the felling process i look to problems in face (unintended duthcmans - kerf, unevenness, rotting failure on one side etc.). A soft face on one side, is like a step on the other side as the soft side gives out. Though that could just be at the upsetting time that the hinge pulls just overloaded, and failure from the L started early from low strength/ flexability, perhaps overloading at the slightes close of face overloading the camels back....

Especially, when going front to back, i think that tapered hinge, fat against the lean (so hinge points at lean side). For to fight that OffSide balance, takes force away from the sweat and leverage of the guys pulling forward etc. If your push starting someone, you want their tires straight to make it easiest to push. So, here the pulling force can draw it forward easier with more force freed up (now that hinge helps carry side lean).

So on front to backs i especially look for that off balance and calculate my tapered hinge position. i think a shallowly placed hinge for this sets more leverage against you (less slant from lean to farther back hinge), and also a shallowly placed hinge needs more arching of the already farther than usual arching hinge (farther back angle to forward). This asking more flexing of hinge and possibly dry /decay would kinda back me down.... But, in flexing hinge more, and needing 2nd stage boost, i give dutch under lean; so that even if hinge flexability fails early from the farther flexing, i got that step in stage 2 to push lean as backup strategy. Dutchman's can be dangerous, especially in felling. They invoke/ reflect the fullest speed, leverage, mass and direction that the falling tree has to offer (when thrown hard), functioning as the faces slam closed.

This is another place where i like that 'Over the Hill" lacing to down low, bracing and pushing that tree forward evenly down it's whole length, can even have it off towards lean a might. Just seems to embrace it, hook it, stabilize and pull it along more surely or something.......

But, i mighta just chickened out on that one all the same, decaying states of wood can be pretty spo:umpkin: oooky even with out the extra gymnastics. IMLHO


Nice puzzle/ exercise thanx, glad noone hurt, just my .02, please don't feel short changed! Figured some of the other fellas woulda jumped on this...... Putt the JPRCS on it or something. What is the cranking power of 12 screaming JP's pulling like the :angry2:soup bowl is at the other end of the rope and were late for dinner???

Hope to meet my connection and do another line of hinges today , like a good'lil hinge freak!

 

[Stumper]

Matt, It sounds like you just ran into the consequences of a bad combination of factors. Felling against lean/uphill is tough. Decaying wood is unreliable. Hollows force narrow sidewalls of a hinge to carry all the load. Cherry is a very low density hardwood whose compression strength exceeds its strength in tension making for what we would term"brittleness". You lost control because you didn't have the material to control it with.-Once the hinge failed there wasn't anything you could do and the hinge was predisposed to fail. A trick you can add when faced with such a situation is to add multiple pull lines set out in a broad V formation- if the hinge fails and the tree collapses to one side the opposite rope tends to swing it back. This doesn't guarantee precision but can keep from having a 70*(or 40*) offline fall. Glad that no damage occurred. Don't beat yourself up-you just learned about some things that you have to watch out for.:angel:

 

[ORclimber]

Don't know if this applies to this situation. Have had/seen tops go the wrong way(w/ perfect face and backcut) because the pull line angle to ground was too sharp. After reading Berenak's book realized that's what went wrong those 2 times.