Re: [CAD_CAM_EDM_DRO] re:Re: Ball screws for CNC plasma cutters

The way I am tackling this problem on the little mill I'm making where it
seems to be Ok is to use screws instead of the spring. The two nuts are made
as rectangular blocks with the screwed holes through the middle of their
longer sides. Then, either side of the main hole are two other holes. These
are for two pairs of screws, one of which pulls the blocks together while
the other tries to push them apart. So, by tightening one pair while
slackening the other, the blocks may be set at an exact distance apart which
removes the backlash while not increasing the drag of the nuts.

Ian
--
Ian W. Wright
Sheffield UK
www.iw63.freeserve.co.uk

----- Original Message -----
From: <ballendo@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: 16 February 2001 06:22
Subject: [CAD_CAM_EDM_DRO] 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>
>
>
>
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