| 摘要 |
A grinding head has at least one expandable grinding tube mounted on an expansion cone. The expansion cone is carried by, and is rotatable with, an expansion rod which is coupled for rotation with a driven part of the head. The expansion rod and cone are movable by means of a ram to cause expansion and contraction of the grinding tube. The connection between the ram and expansion cone via the expansion rod includes helical coupling means whereby to cause a step-down in the effective stroke of the ram as applied to the expansion cone, which enables high accuracy in the expansion and contraction of the grinding tube. |
