My daughter asked for a shelf to put her things on. I found several offcuts that looked like they might work together.
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The first piece is white pine. I took it along to my shop and scored the waste on the table saw then brought it home to work in the evenings. Here I am cleaning out the waste with a chisel.
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Cleaning up the gigantic dado with a wide paring chisel.
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Next undercut the sides of the dado with a ryobi. The first cut was made with the saw flat on the floor of the dado, the second with a spacer.
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Some chisel work to clean out the waste...
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And cleaning it up with rasps and files.