9" is a pretty wide board to begin with and sometimes maple can be a
little brittle; I'm not sure what you mean by "pad sander" but I do't
think normal sanding would produce enough heat fast enough to cause
the cracks you describe. They sound like they are just the kind of
cracks you'd get from using lumber that wasn't dry enough. You
mentioned they were rough cut. Did the mill or lumberyard say what
type of drying they had undergone?


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Larry Wasserman Baltimore, Maryland