My SI SHUI, Shandong, China live center turns hard and rough. It turns so hard that the work usually just slips on the taper of the center. It has been in my collection for a while, only used once or twice--looks like new. There is a slotted head plug in the other end that I screwed out to look inside but got no clue from that. Any ideas how to make this work or am I due for a new one?