Keeping a saw square and plumb as you crosscut a board can be challenging for the novice carpenter, joiner or cabinetmaker. As I was framing in a new half wall in my study over the weekend, I was reminded of a neat little trick to overcome this challenge. I can’t for the life of me recall where or when I picked it up, but I now do it instinctively without even thinking. Its quite simple and only requires a working ear (or ears) to accomplish.
If you are a user of handsaws for dimensioning lumber, than you already know that the challenge is not in starting the cut square, but in keeping it square through the sawing. To start, you can mark your cut line across the face of the board and down the edge, or use the reflection in the saw plate to guide you. But as you start sawing, you can easily go out of plumb with the movement of your body (especially if you’re like me and carry a good 150+ pounds above your waist). The trick to staying square is listening to your saw in the back stroke. If the saw plate flaps like a baseball card in a bicycle spoke as you draw it back through the kerf, then you have angled the saw out of plumb with your cut line.
Think of it like this: your saw plate has to be perfectly parallel with the established kerf as you draw the saw back through it. Otherwise, one side of the plate will collide with that side of the kerf wall. If this happens, the saw plate not yet engaged in the kerf will only enter the cut if it bends. Because saws are made of spring steel, the plate bends quickly and combined with the speed of your backstroke, this makes the plate bend back the other way as well thus creating a fluttering effect as it bends back and forth at a high rate. And this is what that funny flapping sound is when you saw.
So once you hear this sound, you can easily adjust your stroke to true the saw and keep the cut plumb. And the really cool part of this trick is that it works for any angle you need to cut….miters, tapers, splices…any angle. This is because the fluttering tells you that you have deviated from the established kerf angle, regardless of what that angle is. So as long as you start the cut true, you can keep it that way with your eyes closed and your ears open.