Re: [CAD_CAM_EDM_DRO] Re: Do Stepper Motors need "Drag?"

Even 'high end' ball screws are often found with an anti-backlash
arrangement using two nuts to provide preload. This is the only way to get
the greatest stiffness.

Regards Peter

----- Original Message -----
From: <stevesng@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, November 05, 2001 5:46 PM
Subject: [CAD_CAM_EDM_DRO] Re: Do Stepper Motors need "Drag?"


> --- In CAD_CAM_EDM_DRO@y..., tom.kay@n... wrote:
> > Thanks Steve, great feedback. Oh, another quick thought; would
> > leadscrews and plastic nuts be OK for the average hobbiest who is
> not
> > earning money with his benchtop mill? Or is the wear factor enough
> of
> > a pain/expense to go right to ballscrews, in your opinion?
> >
> > Cheers, Tom.
> >
> >
> > --- In CAD_CAM_EDM_DRO@y..., stevesng@n... wrote:
> > > --- In CAD_CAM_EDM_DRO@y..., tom.kay@n... wrote:
> > > > I am converting a mill to cnc with Dan Mauch's 5 amp boards and
> > his
> > > > 521 oz-in stepper motors. I plan on using a 2:1 reduction from
> > the
> > > > motors to the screw.
>
> Tom,
>
> One man's trash is another man's treasure..... I have only seen
> the plastic stuff used in lightly loaded mechanisms and formed
> my opinion based on them. What I saw did not look like it was
> up to milling machine usage, however we live in a world of
> constantly evolving technology. There may be plastic systems
> that can do the job. The "plastic" is actually going to be
> some sort of low friction material, likely a composite. Good
> old Teflon is very low friction, but flows under pressure.
> There are many new composite systems that put graphite, moly,
> or who knows what, into the plastic mixture. This could allow
> a stiffer plastic to have low friction.
>
> Keep in mind that anti-backlash setups work by pressing two
> load bearing surfaces apart and against opposite flanks of the
> screw thread, or some work by squeezing the V of the nut deeper
> into the V of the thread. On high end ball screws, the balls
> are precisely matched to the screw without using two nuts. This
> is the same as pressing the nut deeper into the V of the thread.
>
> Whichever is used, it must have enough force to resist being
> pushed together, or out of the V as the load on the nut increases.
> As with all systems, ability to resist load and rate of wear are
> opposing requirements and must be traded off against one another.
> Some of the other folks on
> this list have done the math for how much force is needed to
> turn the screw. This could be extended to figure the load on
> the nut assembly and give you numbers to check against the
> specs on the plastic nut systems. Whatever the case, in order
> to carry the same load, a plastic nut is likely to be larger.
>
> Until someone shows me a new "miracle" plastic nut system, I
> will continue to recommend ball screws for anything the size of
> a mill-drill.
>
> Cheers,
> Steve Stallings
>
>
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