Based on the equivalence of points contact and distributed contact,we presented the formulations of frictions in typical joints with small clearances on the assumption that the deformations of joints are negligible.

This paper analyzes the problems of the old cab′s door from the aspects of structure,airproof and gemel.

To solve the big bulk, high cost and short life span problem of current vibration tapping and reaming system , and to promote application of the high performance vibration tapping and reaming technology, they proposed a wedge type torsional vibrator, which is of much smaller pressure angle, more compact,and which is symmetry in construction and easy to be fabricated.

Affected by some certain factors,it will appear flaws that hole enlarges when the centre of workpiece deviated from the centre of reaming.