if cnc..do I need DRO??

[camfambmw5]

Question..just picked up a Mint, totally rebuilt to original tolerances, Bridgeport Series I.

My situation is this, I started trying to make something (manual for now) with very tight tolerances and realized right away that I need a DRO...keeping track if turns on a dial is ridiculous. Question, if I plan on converting to CNC anyway (have 3 nice Servos, 3 Copley powers supplies and 4 encoders already + Turbocadcam) Just working on power supply and electronics end. Is there a need to purchase a dro or will I be able to use the CNC xyz display on my computer screen for am ad-hoc dro?. I just don't feel like spending an extra 1200 on a 3-axis dro if I don't need to.

Any help would be greatly appreciated.

John

[Ken_Shea]

John I am quite certain that your controller will have this built in to the software.

Ken

[camfambmw5]

That's kind of what I am thinking...I have yet to make a software decision (besides Turbocadcam), but, the programs I have seen have, what looks like, a DRO screen on them. MACH1 rings a bell

[vacpress]

the DROS on the programs I have used do not seem to be very precision, and the jog motion can be fairly hard to use to manualy machine anything...

however, learning single-line G-code would let you "manually" cnc a part. That might work well.. Another thing to think about is that there are at least 3 or 4 projects on the web for DIY DRO. some are easy, and some are quite complex.

I plan on adding a DRO to both my manual lathe and mill very soon.. I found these perfect computers for $30 at www.halted.com. These Fujitsu Stylistic computers seem to be perfect. I am going to use mouse encoders at first to write some visual basic code that interfaces a simple PIC16f84 step counter via serial. After I get that working, I may build or buy some decent encoders.. One idea i like is using cheapo surplus servos that are much cheaper to buy than the attatched 500counts per rev or higher encoders. 3 of these and a fujitsu stylistic, a pic16f84 and circuit board or breadboard, etc would still cost like $100 probably. I think there is a commercial unit for that.. But this homebrew could have very nice features.

Maybe an old version of Labview on the Fujitsu with a cheap DAQ device and some sensors would make a great larger machine "PLC" style central computer. Not a CNC controller, this could communicate with the operator via its nice touchscreen, and with mach2 or similar PC software. All for around $40-50 all said.. Sensors could include temperature, encoders for linear\rotary, RPM on spindle, real speed and velocity, etc. of axis. Software is cheap to write.. Its the hardware.

Good luck, hopefully i confused the matter well

[HuFlungDung]

Yes, a DRO would likely be a waste for you if you are going cnc.

The exception would be in the case of using linear scales to provide position feedback, instead of the rotary encoders. Your controller would need to be able to accept this type of signal, of course.

I went this route with the cross slide axis of my small lathe retro. This used a very high precision Sony scale, but required a $300 convertor to make the scale's output mimic encoder output signals to feed into the controller.

[camfambmw5]

The encoders I have are rotary type...what GUI software do you guys recomend..I already have a G-code generator (Turbocadcam)....

Also, would the CNC acting like a dro in manual mode still allow for backlash compensation?????

[Bloy2004]

For manually operating your machine check out the DRO350.
at www.shumatech.com It has many features and enables the use of encoder quadrature input or those inexpensive digital scales that use different output. Very affordable in kit form or some individuals on the forum site offer to build it for you reasonably. At least this would keep you manual until you go full-blown CNC.
I found that I needed a "stand-alone" DRO with my CNC setup at least until I can fully control the machine through the CNC without touching the machine(other than setting up)
With "cheap" linear "chinese" type scales and this DRO350, I am able to control quite accurately the machine. Mach2 is unable to provide reverse readout for manual control. Activation of the servos/steppers locks the axes until powered down, and then the communication with the position is also lost.
I had the DRO350 switchable to the servo encoders but found that the backlash through the belts and ballscrews detracted from true position.
In short, IMHO, if you want to go both manual operation and CNC control, have a "stand-alone" DRO. My machine mechanically allows for manually moving the axes when CNC function is off with some drag from the mounted servo motors.
However, Many machines once set up with CNC have no way of manually(hands on) operating the axes.

John Bloy

P.S. Scott Shumate, developer of the DRO350, is possibly working on a backlash compensation feature for his creation.

[Bloy2004]

Originally posted by Bloy2004
Mach2 is unable to provide reverse readout for manual control. Activation of the servos/steppers locks the axes until powered down, and then the communication with the position is also lost.

This is my mistake.....Mach2 DOES have separate encoder inputs for manual usage. Without engaging the servos/steppers, one can still provide manual encoder DRO.
John