Christopher Schwarz once demonstrated a time-honored trick for hand-cutting tenon shoulders. After laying out the joint, he chiseled directly downward onto the shoulder cutline, then made a V-groove by tapping inward from the waste side. This created a channel to guide the saw perfectly for the desired cut.
I decided to try this technique for hand-cut dovetails, and found it worked equally well for starting a cut accurately, which can be the trickiest part of making dovetails. Regardless of whether you’re a “tails first” or a “pins first” dovetailer, it’s not necessary to do this when cutting the first half of the joint, but it’s a smart move when making the mating part. For example, saw your tail board first, use it to trace your pins on the mating piece, then notch the cutlines on the end of the pin board before sawing the pins. It makes starting the cut much easier and ensures that you’re on the money. — Bill Law