re:Re: Ball screws for CNC plasma cutters

Smoke,

The problem with the "spring between" method you propose is as he
mentioned... Any pressure applied greater than the spring will
introduce backlash. To reduce this tendency, the spring is made
stiffer. Problem then is, the spring causes the nut assy. to be hard
to turn and adds undue wear of the screw. That is why this type of
backlash screw is seen less and less today...

What he proposes (although I'm not sure I see it the way you
described) takes advantage of the pressure angle of the acme screw
that I just talked about (earlier post). That is, since the pressure
to "close" the two halves of the split nut is applied at right angles
to the screw, the flank angle will HELP us to get more EFFECT from a
lighter spring pressure. Also, the axial load will again be helped by
this flank angle (with a 10 degree angle,only a small percent of the
force is being directed in an effort to "push the split nut apart").
Yes, these last two sentences say the same thing; from different
directions.

The method is also easily adjusted, allows for wear, and is easily
changed for ballscrews later(you just mount the outer cylinder to the
machine in the same way as the ballnut ; i.e., a threaded end, or a
mounting flange.

Hope this helps.

Ballendo

BTW, the difference in the way we see his nut description is this:
The split nut(hot dog bun. The screw is the frankfurter.) IS captured
by the cylinder which IS mounted to the machine axis. However, the
split nut is constrained AXIALLY by this "cylinder" which contains
the screws and springs to apply pressure to the split nut. It is not
allowed to rotate, IMO.

><snip> I'm sure this would work well....provided you have the room
>to mount it that way. I'll have to go with the spring mounted
>between two captive nuts...which does the same job, allows for wear,
>is EASILY replaced by standard ball screws when the lead screw is
>changed, it need no adjustment and takes up less space.
> Smoke
>
>
> >Hey Smoke,
> >there is a much better way to get rid of back lash.
> >What you propose always will have the back lash as soon you force

the nut.<snip>