Re: [CAD_CAM_EDM_DRO] Re: rolled ball screws

fozzyber wrote:

>What is the diffrence between preload ball nuts, plan ball nuts,
>oversized ball nuts.
>
>

Plain ballnuts have some axial free play (backlash) in them. It is
usually pretty small, .003"
or less. Originally, preloaded nuts have two tracks of balls, with a
spring or some other
arrangement to force the balls in opposite directions, eliminating
backlash until the load
on the screw exceeds the preloading force. These were somewhat tricky
assemblies, so
the manufacturers found they could just build a single, solid nut
assembly with two tracks,
and by putting just the right size balls in it, they could achieve the
same result. This requires
the depth of the ball track and the pitch be VERY consistant over the
length of the screw.

Some people try to make zero backlash nuts by loading oversize balls
into a standard,
single-track nut. Hand fitting a single-track nut for minimal backlash
is not so bad,
but there is nothing in there to limit the force on the balls once you
get to ZERO backlash.
With a two track nut, the force stretches the screw and nut. With a
single-track nut,
the force on the tracks and the balls can become extreme, causing very
rapid fatigue
wear on the balls, nut and screw. I would not accept such a kluge on my
own machine.

Jon