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

Tony Jeffree <tony@...> wrote:



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.

/// I agree, that would be a good use for one horizontally on a machine having a limited envelope. The biggest drawback with a rotary table is backlash. Adjust it out and it seems like its right back again . I had a 12" Troyke, about $1200.00 and it was the same way. I wonder about compensating for this in the A-axis config of our CNC programs. Endmills, especially roughers will find it really quick and at the most inoppertune times. I've used rotary tables for machining helix's in a manual. Mounting the rotary table vertically atop a plate mounted on THK rails and backed up by a die spring to hold tension against a cam mounted on the circumference of the rotary table that followed a cam follower bearing mounted to the table of the mill. It worked great but, it took 8 hours to set up. Not much money left in the job.



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




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