Another thing that can happen is that the workpiece is not really flat. Even with clamps, you might have Z problems if the clamps are not holding the piece down everywhere. Even if the piece is “flat” against the spoilboard, if may not have uniform thickness. So, in addition to leveling the spoilboard, some level the workpiece before carving with a “roughing” cut. Not trying to be a rich-bitch snob, but pay the money and buy Vectric s/w. It’s much more capable than Easel, not that it’s the problem. Finally, and I don’t know what you’re doing exactly, but buy good wood at Lowes or Home Depot although I buy hardwoods cheaper from North Carolina. I know that some are able to carve the Mona Lisa from pallet wood, but with a million CNC variables, one shouldn’t start there.