I was looking at my garage door one day and noticed the stiffener channel running the 16 foot length (4.88m) seemed to be rather straight, so I put up a string line to see what it may be and found there was only about a 1/16” dip (1.59mm) over that distance. Very impressive I thought; that is more than satisfactory to use as a straightedge gauge when inspecting and sorting planks for cutting & jointing purposes
Step 1: What Does It Tell Us?
Crook and bend show up readily against the channel and their area, dimension, and location can be precisely marked out.
Step 2: What Else?
Edge wane can also be detected and calculated for determining overall useable lengths in a workpiece as well.
Step 3: What's Next?
Using the findings, I set about the task of truing up one side of some nominal 2 X 6 x 8 ft. stock (38.1 X 140 mm X 2.44m). In the image I shimmed this end of a crowned board to fair it up for attaching a temporary straightedge:
Step 4: Ready to Rip
Next I attached the straightedge that will ride against the saw's fence, making sure it was in full contact with the channel.
Step 5: Do It to It
Finally, I ripped the workpiece on my radial arm saw to a smooth and flat edge and removed the guide board. To finish, I then ripped off the widths that I needed for my project using the newly established straight edge, and crosscut them to length.
This method now saves me the difficult process of truing up one edge of a long plank to use as a gauge for its companions, and the door rail is, of course, always available and self- storing.