Chris Schwarz, the editor of Woodworking Magazine demonstrates how to use the reflection of a workpiece on a saw blade to make accurate 90 and 45 degree cuts. It all centers on our innate ability to easily recognize straight lines and 90 degree angles to very high accuracy,
It really works. I’ve used the technique many times, especially when rough cutting wood. A couple of days ago, I made some bevel cuts on the ends of simple 2 by 4s. I marked them, but found it none to easy to observe both faces of the cut at the same time. Checking the saw blade, I found that the reflection trick indeed works for this kind of cut.
The line labeled “1” keeps the cut square or directly on the 45 degree line. The line labeled “2” keeps the cut plumb across the full depth. The keen observer will note that the photo (click to enlarge) shows the reflection a degree or two out of kilter. That’s from holding a saw in one hand, a board in the other, and the camera … you get the idea.
The end result shows that the technique works. (Ignore that little bit of tear out on the far edge, an unintended consequence of stopping to take pictures.) The finished cut is very acceptable for the intended purpose, obviously not a fine furniture project.
Click on any image to show a larger version.
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