On Sat, 2008-02-02 at 11:57 +0000, [EMAIL PROTECTED] wrote: ... snip > a/ DRO (with pukka glass scales) is a huge boon to any manual mill.
Agreed. I write all my way-points with a sharpie on the vise or table before hand so, I don't know what I would do without a DRO of some sort. > b/ A DRO could almost pay for itself in calibrating the screw etc mapping > in emc, both initial set up and then monthly re-calibration, unless of > course your time is valueless. My ex-DRO was too complicated to use other than as a straight position display making any features it has useless. > c/ A DRO beats EMC as a fake dro ONLY, sans servo/steppers, see point b/ > re time. >From my point of view, an EMC based DRO will beat a standard DRO because I have plenty of free PC's with color displays and printer ports. Why pay for something you don't need? Just buy some scales, sprinkle on some HAL and pyVCP and you're done. Plus, with minor additions you can control the spindle, mist, whatever. But wait, there's more, you also have a migration path to EMC. > d/ a DRO can enhance the functionality of EMC considerably, injecting > trustworthy positioning data into EMC to re-calibrate screw etc mapping on > the fly. No, EMC an the DRO get the same information from the scales. The only time the DRO might be necessary is if the parallel port can't keep up with the the data rate. In which case you could go with an interface card with hardware counters, like the Pluto(?) and others. Otherwise, you would have to filter the scale data through the DRO which won't add anything to the data and will impose restrictions due to how the DRO would interface to EMC. > e/ For NC then EMC is obviously the answer, since EMC is likely to be part > of a DIY installation, a DRO makes making all those NC conversion parts > that much easier and faster... the rule of thumb is between 50% for simple > parts and 90% for complex parts, for time setting up vs actual making > chips time, see point b/ re time again. There is less "waste" with having an EMC based DRO from the start. > f/ A DRO + EMC / NC system means redundancy, *lots* of things have to go > wrong before you're knocked back to a pure manual machine. I don't think redundancy is that important. If you have a good e-stop system and something breaks, you're just not machining until you get it fixed. If what is broken happens to be a PC, you probably have a spare one loaded and ready to go. > g/ So the trick here is getting that electronic feedback loop, either from > the DRO or from the glass scales themselves, into EMC, lacking that > electronic feedback loop, putting operator pauses into the gcode of a dual > system still allows periodic operator visual checking of agreement on > position. > > h/ lacking a DRO, the answer is to retrofit my machine with precision > ballscrews and to scrape the ways etc, a prospect that will take about ten > time the time of fitting a DRO and cost at least five times as much in > money. I agree. I think an EMC based DRO is a good way to enhance a manual machine, changing or spending as little as possible. > > i/ I guess this is going to come down to a philosophical choice, do you > pursue the DRO first, or the EMC + NC first? vi vs emacs anyone? > > cheers I realize I may have missed something along the thread which would change everything I have said here. I also failed to consider fitting rotary encoders to your hand wheels, sparing the expense of linear scales. An argument for linear scales is, they give you your actual position without having to guess at things like backlash. My counter is, that you still need to use good manual machining practices to deal with backlash and positional stability problems. Coming up to a dimension from the same direction for each pass, is needed to take up backlash and preload the system against the cutting force. Backlash elimination and preload beats a sloppy, but accurate initial position. Linear scales can mask the need to pay attention to real world machine dynamics. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending) ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
