I recently completed this little shelf unit for my wife to use at craft sales. It will sit on top of her table.
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The back pieces are tongue and grooved together and into top and bottom rails. The middle inch or so of each vertical piece is glued to the rails.
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The finish is satin wipe-on poly. This is the first time I have used this, and I found it relatively easy to work with. But, then, my finishing skills are such that I have to work hard just to reach the point at which I can say, "well that's not completely horrible."