plunge cuts take steady nerves. the way i was taught was to start with the bottom round of the tip of the bar, then slowly tilt the saw up to perpendicular (if that's the kind of mortise you want). as you come up to a straight plunge in you open up a little space above the bar so that the teeth coming back at you don't kick back. easier to control with an electric saw. keep the hand in front of the brake. wear a face shield.
pretty frame Mark. i like the understated, just-because through tenon.
