Re: [CAD_CAM_EDM_DRO] screwless focuser was Re: re:Re: Re: Is this too nuts to consider ?

Yea ballendo,
These are used alot in labs. They last much longer than leadscrews and are as accurate as most, but it's easy to loose position
on the shaft. The three bearing head acts like a slip clutch to prevent damage.

ballendo@... wrote:

> Smoke,
>
> Imagine one end of a solid rod shaft supported by three bearings (the
> outside of each bearing "rides" against the shaft, like centerless
> grinding). The three bearings are radially spaced 120 degrees apart.
> Assuming the bearing axes are parallel to the shaft, spinning the
> shaft will work as expected (the shaft will be supported and spin
> freely, AND will not advance longitudinally).
>
> NOW imagine that one or more of the bearings' axes is NOT parallel to
> the shaft... As you spin the shaft, it WILL 'creep' longitudinally,
> and the amount it moves will be determined by the amount of the
> bearing(s) mis-alignment. Note that if the misalignment is not equal
> between ALL the bearings, there will be 'fighting' among the three
> bearings...
>
> So if we INTENTIONALLY 'skew' the bearings at the pitch angle of
> the "thread" we want to create, the shaft will move longitudinally
> (in and out, toward and away from the bearings) JUST AS IF the shaft
> WERE threaded!
>
> Hope this helps.
>
> Ballendo
>
> >If you eliminate the grooves, what surface are the bearings going to
> >follow?
> >Smoke
>
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