Re: [CAD_CAM_EDM_DRO] Re: DRO meaning in the Artofcnc world

jmkasunich wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, Art <fenerty@a...> wrote:
>
>
>>Hi:
>>
>>BTW: Sorry for all the confusion about DRO, but my background
>>is in electronics where DRO stands for D igitalR eadO ut , at
>>the time I didn't realize it also stood for "Da numerical
>>Readout indicating position stored from counting encoder
>>pOsitioning data". ;)
>>
>>
>
>LOL!
>
>It does literally stand for Digital ReadOut, but in the machining
>world is understood to mean <D>igital readout of <R>eal p<O>sition.
>
>DROs were first applied to _manual_ machines. The DRO eliminates
>the drugery (and errors) when counting turns of the handwheels.
>It also accounts for backlash, wear of leadscrews, etc. Of
>course to do this the DRO must directly read table position, and
>all _real_ DROs do exactly that - usually using a linear scale
>connected directly to the table and completely independent of the
>leadscrew.
>
>I believe words that have specific meanings to end users should
>be used correctly, or not at all, to avoid confusion. I don't
>think for a second that Art is trying to imply that his displays
>are a "real" DRO. However, a machinist could easily draw the
>wrong conclusion.
>
>And to be fair, I must admit that EMC's displays are not real
>DROs either, IMHO, because they show the position of the leadscrew,
>not the table or tool.
>
>

Well, this isn't **EMC's** fault! It is because we are a bunch of
cheapskates,
and a high resolution shaft encoder is a LOT cheaper than a high-resolution
glass scale. I got some Sumtak 1.25" 1000 Cycle/Rev encoders surplus for
$75 each. On the X and Y axes, I get a resolution of .00005" (50 uIn) and
on Z i get .000025" (25 uIn). Try to buy a 25 uIn glass measuring
scale, but
be sitting down when they tell you the price!

I got some decent, but much lower resolution scales on my new lathe, and may
try hooking them up for CNC motion control. These are the typical .0002"
(roughly - they are really 5 uM) DRO scales that most machines use.

And, note that with any of the available encoder interfaces for EMC, it WILL
work as a conventional DRO, measuring machine movement when it is in
E-stop mode.

Jon