# Dro & cnc



## JPigg55 (Dec 20, 2012)

Question ????
I'm considering a future CNC conversion, but want to have DRO on my mill now.
I'm assuming one still needs to mount scales for a CNC set-up.
Can CNC software be used for the DRO indications without having full CNC conversion ???
Another way to put it. Will it work if I mount DRO scales (I'm assuming cheaper to buy without display) and connect to computer with CNC software and be able to use the DRO readout while using manual control ???
Or would I be better off with a standard DRO for now and worry about CNC when I've made the choice ???


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## Kylisdad (Dec 20, 2012)

To the best of my knowledge, CNC machines use stepper motors and Encoders to control machine position. I don't believe they use the same linear scales that a DRO uses...


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## Shabtai (Dec 20, 2012)

I installed a DRO which I used for about 2 yrs before finally converting to CNC.  I did remove the DRO and scales.
you could use the scales with Mach3 s/w for accurate positioning.  Since I used heavy (400oz) steppers I felt that
the s/w could keep track of table position as long a there were no missed steps.  In 3 yrs of use have not lost a step.
If you use servos you might want to keep the scales.  You can also use steppers or servos with built in encoders, again
eliminating the need for the scales. good luck.


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## DMS (Dec 20, 2012)

That depends on a lot of things. In general CNC machines do not use linear scales. They either use stepper motors (open loop control), or servomotors and encoders (closed loop control). Usually the encoders used for servomotors are rotary encoders, but it is possible to use linear scales with a cnc system in place of, or in conjunction with a rotary encoder. That all depends on whether you can get a signal out of your DRO that your CNC controller can read. I am not familiar with any that do this. Keep in mind, this is a pretty uncommon setup (I have never talked to anyone that has done it, only heard mentions to it), so it's likely going to be challenging to set up. 

Another thing to think about is that, with a DRO, once you have gone to CNC, you can use the DRO to map the ball-screw. This will allow you to work with lower end screws, and still achieve great accuracy. My recommendation would be to not worry to much about working the DRO into your CNC conversion.

-DMS


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## JPigg55 (Dec 20, 2012)

DMS said:


> Another thing to think about is that, with a DRO, once you have gone to CNC, you can use the DRO to map the ball-screw.-DMS



Thanks for the info, as you can tell, I don't know much about CNC hence I'm not sure what is meant by "use the DRO to map the ball-screw". Kind of sounds like using the DRO to find the inaccuracies in cheaper ball screws.
If I go CNC, I was planning on going the closed loop servo route just due to other advice received.
Sure makes the DRO choice hard. If I go for a cheap one and don't go CNC....
Guess another option would be to get a better DRO and put it on my lathe if I CNC the mill.


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## jumps4 (Dec 21, 2012)

I was thinking about using scales and a kflop controller but the system has to be coded by hand and is only good for stopping if there is a motion error detected not a correction.
i followed their users group for about a year before building my mill and decided it was not worth the trouble or cost.
steve


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## GaryK (Dec 21, 2012)

Scales will give you your true and actual position whereas rotary encoders well only tell you that your motor has moved a certain amount.

Suppose you setup your system to say that you have 2000 steps in one inch, but in reality it's 1999.999. A rotary encoder will verify that you have moved 2000 steps,
but a linear encoder (scales) can tell you that you have moved one inch regardless of how many steps it took to get there.

Linear scales are far superior to rotary encoders in that they will give your true position regardless any slop or cumulative errors over distance.

The only caveat to this is accuracy of your linear scales.


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## JPigg55 (Dec 21, 2012)

Guess I got more research to do.


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