Re: Vertex Rotary Table Backlash

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "alex" <telecomt@t...> wrote:
> In this case, why not to build rotary table driven by the belt/chain
> directly from
> stepper, with no worm gear involved?
> Alex

Because you need the high worm ratio to prevent cutting forces
driving the table. Try turning a 10:1 gearbox the wrong way, it's not
that hard and to get a high enough ratio that would prevent run back
on chain or belt would be an enormous ratio and physically impossible
to fit in.
This is one application where the worm and wheel is ideal.
Backlash if not excessive shouldn't be a problem as you should always
go one way and the commercial units such as the Vetex are very good
in this respect. Far better than most of the home made gear we had to
put up with before the advent of this small affordable equipment.

John S.

> ----- Original Message -----
> From: bazer_20002000 <b.smith@b...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Monday, May 26, 2003 3:23 PM
> Subject: [CAD_CAM_EDM_DRO] Re: Vertex Rotary Table Backlash
>
>
> > Hi Im not familar with the Vertex system however you could

consider

> > junking the worm wheel and fitting an adjustable zero backlash

unit

> > (ie the worm wheel is split down the middle). These can be costly
> > but this depends on the size needed and how much you want to cut

any

> > backlash out.
> > Barry
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Andrew Mawson"
> > <andrew@m...> wrote:
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...>
> > wrote:
> > > >
> > > >
> > > > fuddham wrote:
> > > >
> > > > >I have converted my 6" Vertex rotary table to CNC. What is

the

> > > best
> > > > >way to minimize backlash? What is the typical amount of the
> > > backlash
> > > > >on these tables? Also, has anyone used some sort of indexing
> > > (rotary
> > > > >table) to mount several vises on and index the vises to do
> > several
> > > > >parts with the current tool instead of several tool changes

for

> > > just
> > > > >one part then start all over again?
> > > > >
> > > > >
> > > > Assuming the backlash is between the worm and the wormwheel

that

> > > drives
> > > > the table, there is a limit to what you can do. First, you

may

> > > have a
> > > > mechanism
> > > > to adjust the space between the worm and the wormwheel. Some
> > units
> > > have
> > > > eccentric bushings on the worm that allow the engagement to be
> > > adjusted.
> > > > If not, it may be possible to make new eccentric bushings.

But,

> > > some worms
> > > > may be cut in such a fashion that you can't reduce the

backlash

> > to
> > > zero.
> > > > It may be possible to take a little material off the peak of

the

> > > thread by
> > > > turning the worm on a lathe, to allow the threads to engage
> > deeper.
> > > > The high-end drives use a split worm, with some kind of

mechanism

> > > > between the two halves to keep a preload on them.
> > > >
> > > > Jon
> > >
> > > fuddham,
> > >
> > > On my 4" Vertex I stripped it right down, cleaned out the road

tar

> > > that they seem use as a lubricant, re-oiled it, and set the
> > eccentric
> > > bush so that I could just feel the high spot when turning by

hand -

> >
> > > this brought the backlash down to 'reasonable' but I haven't
> > measured
> > > what 'reasonable' is.
> > >
> > > I seem to remember it being suggested (?? by Tony Jeffree??)

that

> > it
> > > is worth 'running in' by mounting it so the lathe or some other
> > power
> > > source turns the worm & wheel while meshed to bed them together.
> > This
> > > will take off the highspots and let you get a lower backlash
> > figure.
> > > Logically, as the running in progresses you should adjust the

mesh

> > > closer - I suppose its a sort of lapping action.
> > >
> > > BTW I like your idea of multiple parts being processed while the
> > tool
> > > is still in.
> > >
> > > Andrew Mawson
> > > Bromley, Kent, UK
> >
> >
> > Addresses:
> > FAQ: http://www.ktmarketing.com/faq.html
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