Sudden vibration happens to the main machine body

The reasons are:

(1) Parts are not fastened;
(2) Bottom screw cap is loose;
(3) Main shaft is bent to be distorted and the weight of some part is unbalanced.

Solving method:

(1) Check the firmness of each component;
(2) Tighten the screw cap;
(3) Replace the main shaft and adjust the balance degree.