I have been making coasters from kiln dried wood. My process is gluing several pieces of wood planks together (varies from 3/4 to 6/4 until I get a 6" thick blank), then cut the shape on a band saw (end grain perpendicular to the table). I stain the edges and then run the shape through to cut 5/16" pieces (end grain parallel to the table). after I completed staining and poly on them, I noticed that some of them are bowing and twisting slightly resulting in them not being flat. This had to have happened after I cut the slices as I checked to make sure they were all flat before I completed them. Any ideas on how to fix these, why this happened? and how to prevent in the future?