I have found a De Walt radial arm saw MOD # MBC, REL # 27 SERIAL #, 116595. All the movements are functional, except getting the saw to unlock from the arm to make a crosscut. There is a red knob on the saw handle that seems partially in & out. Is this my problem? I cannot see how this has linkage to a lock on letting the saw slide in & out on a 90 degree crosscut. I got this saw for free, what am I doing wrong? I feel have found a treasure, & would love to recondition this saw. Please help me. I don't feel inept. I have a lot of success with automotive & small engine repair. I would like to hone my skills in woodworking. Please tell me if this project is worth it or not.