Mortise & Tenon - For this joint, I recommend cutting the tenon first. Use whatever method you prefer to lay out the tenon, but I recommend basing the thickness of your tenon on the tool you plan to use for cutting the mortise. Once the tenon is cut to size, lay it across the mating piece so that the top and bottom of the tenoned piece are in the proper position, then use the tenon itself to mark the top and bottom boundaries on the mortise piece. If you sized your tenon to match a rotary cutting tool, such as a router bit or mortising drill, simply mark where the center of your mortise needs to go and start cutting. If you like doing things with meat power, use the tenon to mark both edges of your mortise. It is much more accurate to align your chisel between two marks that match its width than to center it along a single line.
There are times when it isn't practical to use the workpieces to gauge against each other. For those situations, there are many tools available for transferring dimensions from one piece to another. Dividers, calipers and trammel points can all be used to positively transfer measurements from one piece to another.
Accurate marking is the first step to joinery that fits well and looks good. Take advantage of these simple techniques to ensure your projects get off to a great start! 4WM.