Crupiea, the ones I am familiar with have a "nut" in the handle. Turning the handle tensions or releases the blade. Some have a short rod sticking up at each end of the blade. They allow you to rotate the blade relative to the frame to ease cutting near the limit of the frame.
Good luck with the hand work, I could never get it to work well, I either broke the blade or couldn't follow the line, or both.
Jim
