Re: [CAD_CAM_EDM_DRO] Re: rotary table as 4th axis

At 20:06 27/10/2004, you wrote:

>Jon, I agree. Rotary tables have no chuck generally making setup more
>difficult in a vertical configuration. Using them horizontally is waste of
>time because any 2-axis CNC machine is more than adequate for any
>machining that the rotary table would be capable of. In short, rotary
>tables are dinosaurs for CNC. To use them vertically means if they have no
>90 degree plane they have to be mounted to an angle plate. And to run
>between centers involves the use of a lathe dog and a tailstock. Or mount
>a chuck on their table which involves dialing in and all that. For my 4th
>axis I use an tilting index head with integrated 3-jaw chuck. Its ability
>to tilt makes possible the helical slotting and machining of cones or
>tapered diameters. A rotary table can do this as well but involves a huge
>sine plate. And they arent cheap. Find an old tilting index head and throw
>a servo on it. They are much more massive and precision with regard to
>their gearing and the ability to take up all backlash. I had
> two rotary tables an 8" and a 12" when I got my CNC up and running they
> went Ebaying. They're for manual machines, not CNC.
>

Ron -

I'm afraid I disagree with you (and Jon) on a number of points.

There are several rotary tables on the market that are inherently able to
be mounted horizontally or vertically. Often they have a taper bored in the
centre of the table - MT2, MT3,..etc., allowing very simple adaptation for
use of chucks, collets,...etc. if need be, effectively converting them into
dividing heads. There is a useful difference though - many of the rotary
tables are 90:1 drive ratio, as opposed to, say, The B&S dividing heads,
which are 40:1. In CNC use, this gives a useful increase in both resolution
and available torque at the table. They are also considerably cheaper than
a dividing head of a corresponding size. Granted, you don't get any tilting
capability, but that can soon be added by means of a tilting table, and
still leave you with change out of the cost of an equivalent dividing head.

As for using a rotary table with its table in the horizontal plane on a CNC
mill, there are actually occasions when I have found that to be useful -
for example when engraving a clock dial that was too large a diameter for
the Y travel of my mill. The alternative approach, engraving the dial in
two halves using register pins etc., would have been much less convenient
and the quality (invisibility) of the "join" on the dial would have
critically depended on accuracy of registration.

So, for my money, a rotary table can actually be more versatile and better
value for money than a dividing head. Of course, for ultimate convenience,
maybe you need both... ;-)


Regards,
Tony