Jeshua Lacock wrote: > On Jul 20, 2012, at 9:13 PM, Stuart Stevenson wrote: > > >> Andy's solution is the correct solution. A string will fold under >> compression. This will allow the supports to collapse together when the nut >> moves their direction on the screw. The string will pull the supports along >> with the nut and allow the supports to space themselves along the screw >> with the spacing equivalent to the length of the string sections. >> >> The 5 axis Cincinnati machines in my shop have .007 to .009 in >> preload/stretch. >> > > Hi Stuart, > > Thanks for the clarification! > > I am not sure what yo mean by preload/stretch though. > Bearings at each end of the leadscrew STRETCH it across the frame of the machine, literally making the screw a few thousandths of an inch longer. This raises the natural vibration frequency moving the critical speed up, as well as prevents the screw from buckling under compressive loads. As long as the forces applied at the ballnut are less than the tension, then the screw remains under some tension.
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