Hi Fred,

Like you sometimes those fancy tools are just too expensive for one to swallow. But with a little ingenuity and a small bit of work you can make something that will give you a perfect center every time. I made up this tool using some scrap balsa and it works great for me and will give you repeated results and a straight line. Search around your scrap box for a block of balsa that is half the thickness of your hinge surface. Glue that block of balsa onto a piece of balsa sheet and then harden the block of balsa that serves as you knife blade guide. To use the tool just place it against the surface and let the xacto blade rest against it and let it guide your cut. Flip the tool on the other side and make the second cut. Remove the cuttings and then mount your hinge. I have several of them sitting around my shop for the various planes I built. The one I show in the photo's is obviously not for this airplane since it's not centered. Photo's probably show a better description:


Hope this helps...