Re: rolled ball screws

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo <ballendo@y...>"
<ballendo@y...> wrote:

> Torsten,
>
> The rolled screws will need the variability of the "flexible"
> coupling. GROUND ballscrews can use a fixed length coupling.

Yes I came to the same conclusion, the cheap rolled screws
will never be able to be adjusted as close to Zero Backlash
as a precision ground screw.

>
> The Mfrs know what they're doing... The preload spring is chosen
> based on the anticipated loads you expect to see in your

application.

> This means that the flex will only happen if you exceed your design
> specs (or if you get the wrong screws<G>)

Sure they know what they are doing, and if they offer the nut
as a Preloaded Ballscrew assembly there is nothing wrong with it.
But if it is offered as a zero Backlash Nut this would be
missleading.
A rolled ballscrew with this preloaded Nut would only run
true in one direction, going the other way will flex by the
amount of backlash under the load of a cutter.
The specs are not designed to overcome the forces encountered
by a cutting operation on any mill.
(the amount of preload required would be unreasonable)
Unfortunatly this force depending on its direction may also
affect some other axes's that are not moving.

The reason this is bothering me is that I was totally unaware
of this and I have read alot information that was available
at the bigger MFG's, seams they don't want to point this out.
If you spent $400.- on a nut don't you want to know what your
getting?

>
> Hope this helps,
>
> Ballendo
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "torsten98001

<torsten@g...>"

> <torsten@g...> wrote:
> <snip>
> > This backing off is just the thing I am talking about.
> > If the backlash of a single nut is lets say 0.004 inch
> > then backing off the second nut by this amount or more
> > would reduce the function of this arangement to be a
> > mere damper when movement against the spring exeeds the
> > amount of preload.
> >
> > This will probably result in a nice feel of motion on the
> > spindle because the torque of turning will be very constant
> > over the entire range of travel even so the effects may be
> > elusive.
> >
> > On the other hand a Fixed position of the two nuts would
> > result in a feel that makes any variation in pitch on the
> > Screw very noticeable by requiring more torque to overcome.
> > But this would allow adjustment to reduce the backlash effectivly
> > in both directions to the amount of the largest pitch
> > missmatch within the length of the two nuts.
> >
> > Question is what is most practical under real conditions?
> >
> > Are the big MFG's of preloaded Nuts "full of it" for insulting
> > our intelligence for offering this kind of solution
> > Or
> > is this the most practical way of doing it?
> >
> > What is your take on this?
> > Thanks