What? Bumper stump? No-move crane pick? Is this article a poor English translation of another language?
Let’s clear this up: This article describes a type of cut made to the butt log of a tree to hold it perfectly still during a crane pick. This cut would be useful in situations where that log must not move or it will hit something very close by as it is lifted off the stump. Think of a giant tree growing way too close to a house and you need to pick that log without it swinging into the tile roof. Or the teak deck it is growing through!
This cut is commonly known as the flare-lock cut. Basically, the chain-saw operator cuts protruding tabs, feet or “bumpers” into the base of the trunk flare that keep the piece from swinging around as it is lifted off the stump. It also lets the operator reposition the boom above the center of gravity of the piece, if needed. Pretty neat, huh?
The flare-lock cut needs to be a controlled pick. Set two continuous round slings at 180 degrees from each other on the top end of the trunk to create balanced, vertical chokers supporting the stem. The 180 degrees assumes the trunk is a perfect cylinder; if it is out of round, position the slings around the trunk in a way that balances the center of gravity. Leave plenty of sling length to connect to the crane.
Select a saw powerful enough to cut all the way through the piece to assure there is no chance of leaving holding wood as the piece is lifted. Start the cut on the bad side or the hard-to-reach place and work toward the good side or comfortable position. Position the saw dogs (or felling dogs, spikes on the saw body that wedge into a tree to hold the saw still as you cut). This is the first bumper. Make a level cut into the bole. When the tip of the saw reaches the back side of where you want the first bumper, remove the saw. Reposition the dogs to where you want the next bumper and make another level cut into the tree. Repeat for the third bumper. Three feet are very effective at holding the piece still. But if you can only cut two feet, make them both on the side you are trying to protect.
After you make the through-cut kerf, create the feet by making “dog-ear” cuts into the stem.
Here are some additional tips for making the flare-lock cut:
• Position yourself so you can see the cut as it is being made. You don’t want to end up cutting through the feet if you can’t see them.
• Make a clean through-cut. Do not make the crane have to tear or force the limb off.
• Make your cuts with confidence. If you are unsure or hesitate with your cuts, the chances for an unexpected situation increase. The more you train and practice in non-critical situations, the more confident you will become.
• Make sure the crane hook is located directly above the center of gravity as much as possible.
• Pre-tension the slings to remove the slack. If there is any slack in either sling as the piece is lifted, the piece could spin or move outside the bumpers, and there go all your best efforts to hold the trunk in place.
• Follow the load charts precisely and always allow room for error, especially when working toward the outer limits of capacity.
The tree needs to have some trunk flare in order to create the feet/bumpers. This is a cut that needs to be practiced in non-critical situations before attempting it for the first time on a job. Practice making the bore cuts without cutting off the feet.
Don’t use this method if you only have one strap. You will need at least two continuous round-slings to balance the trunk. Substantial tree lean may also contribute to movement when cut.
Tchukki Andersen, Certified Treecare Safety Professional (CTSP) and Board Certified Master Arborist (BCMA), is TCIA staff arborist.