Aside from the previously mentioned not being able to see through them for positioning, some other things to consider would be what happens if you slip off and hit the wood with your needle? When this happens with the plexiglass templates it usually breaks the needle or chips off a bit of the plexi depending on the angle of impact. (can also throw your machine out of timing) Even the most experienced LAQ will slip and hit a ruler. I can envision the needle getting embedded in the wood and no way to get it out. Personally I would not attempt to use wood as a LA template. I also know of a LAQ who uses her wood working saws to make her own plexiglass templates. She uses 1/4" plexi. I think I would do that long before I would make them out of wood.