I sharpen my own hand saws, and I have designed a wooden saw vise from scrap that presents some improvements over other alternatives. My vise has two sets of independent vertical arms that transfer the clamping pressure of a bench vise to the wooden jaws that hold the saw blade. The vertical arms are connected to one another by crosspieces at the bottom. The advantage of this design is that the bench vise screw and rods do not interfere with the clamping of the wooden arms. You can also clamp the saw blade as low to the bench vise as you want to apply more pressure and transfer less vibration while filing the teeth. I can clamp everything from small dovetail saws up to a 28″ rip saw by using narrow strips of wood for the contact surfaces of the jaws.
The vise measures 141⁄2″ long by 12″ tall, and the arms are spread far enough apart to fit around my vise hardware.