Here are two shop made tools - a 24" long square and a 6" long smoothing plane;
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When laying out crosscuts for wider panels, the 14" Marples T-square I've had for 30 years sometimes isn't long enough to mark the full width of the cut.
Inspired by Jim Tolpin's's book "The New Traditional Woodworker" (which I highly recommend), I built this cocobolo and maple square with a 24" long blade to fill this need.
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I am strictly a hand tool guy so I don't work to the exacting tolerances of some folks, but based on the "draw a line, flip your square, draw another line and see if they're parallel" test it turned out to be more accurate than expected.
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Continued below