By urbanforestryassociates, Jun 6 2016 09:34PM
We got a new toy recently at UFA. Our Resistograph was getting a little outdated, so we decided it was time to upgrade our hardware and boy are we glad we did. If you're like most, you have never heard of a Resistograph, but it's basically our way of getting an idea of what's going on inside your tree. In the previous model, a thin drill bit entered the tree, driven by a Boshe cordless drill and the resistance on the torque of the bit was graphed on a long sheet of paper. When it encountered a hollow decay cavity inside the tree, the resistance dropped off and we could get an idea of how thick the wall of sound wood was. It was a good tool and aided quite a bit in our assessments, but the new model is really next level stuff.
First off, it's all digital. This lets us more precisely control the speed of the drill and keep more precise records. More importantly, it reads both feed resistance as well as torque. Don't let me lose you here, it's not that bad. The torque reading is what we had on the previous model and is just the resistance on the bit as it turns. This typically increases as we move through the tree as the hole gets clogged with sawdust and that can lead to possibly missing a cavity.
The feed resistance is what really sets the new model apart. This is how hard it is for the bit to move forward into the tree. Neither reading is a perfect indicator of decay, as there are specific conditions that can fool each one, but working together, we can get a much better picture of internal conditions. Specifically, the feed allows us to pickup pre-decay. This can tell us that a wall of wood that shows as 5" thick according to the torque reading is actually only 2" of sound wood and 3" of wood with pre-decay, which does not have any significant structural strength. This is a considerable difference and can make the difference between a safe tree and one that needs to be removed before it falls.
Hopefully your tree won't need our fancy new tool. But if it does, you'll be glad we have it.