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

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