Re: Vertex Rotary Table Backlash

--- 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