I needed this idea the other day, but I can't remember what for. :P How to Build an Easy Glass Bottle Cutter made up of Common Parts DIY Project - The Homestead Survival - Homesteading Re Purposing Tool
Draw a circle with a square - Tack two nails to set the diameter you want, then rotate a framing square against the nails while you hold a pencil in the corner of the square. Rub a little wax on the square so it slides easily.
DIY Wood Working Tools For The Beginner - Jackie @ Teal Lime recommends her favorites along with a few personal examples of how she used them with her own projects. Gotta love it! - My Easy Woodworking Plans
Veritas® Transfer/Log Scribe :: The Veritas transfer scribe is used for transferring the contours of one shape onto another. This is what makes it an ideal log scribe. But this also makes it an excellent carpenter’s scribe .