The incision is not straight or the splint is not clamped. Eccentric flaring device is often used to make the bell mouth of copper tube, and the bell mouth made will not deviate, so the sealing performance is better. When the expander expands, deviation occurs due to uneven incision or unclamped splint. Don't use too much force when cutting the pipe, and try to hold the splint instead of the copper pipe when flaring.