Chris Marshall: Does your jigsaw have roller bearings that provide additional support behind the blade? Most newer saw models do, and they can help prevent blades from flexing during cutting. Sounds like you've already tried shorter and wider blades, but make sure to switch to a new blade as the old one dulls. It will take more effort to drive a dull blade through wood than a sharp one, and the harder you push the tool, the more likely the blade will flex in the cut. You also might be having more difficulty based on how you are using the saw. Give the blade a chance to cut the wood; slow down your feed rate so the blade isn't playing "catch up" with the amount of pressure you're applying to the tool. And take extra time when sawing curves. If all else seems to fail, cut outside of your layout line to leave some waste, then clean it up with a router and a shaped template or a straightedge guide and piloted straight bit. Sure, routing is an extra tooling step in the process, but you'll be ensured of dead-square, clean edges that way.