On Sunday 03 May 2009, Rob Jansen wrote: >Doug, > >I've seen the responses from other stating it's "kind of OK as long as >you watch out". >Well, I can tell you it's not OK. > >Use the cable for anything but steppers, servos, encoders, limit or home >switches etc. >I have seen problems even when the spindle's VFD signals and stepper >cables were all shielded - that's proper shielded Olflex cables >especially made for machine controls - and things like unwanted limit >switch triggers or steppers 'walking away' are not uncommon and very >hard to fix once you have everything boxed and ready to run. > Can you describe this Olflex cable please?
Using the cable I mentioned, with the computer, stepper psu, and xylotex driver box all on a shelf about 2 feet wide, located at ceiling height in my little shed. I've had zero problems of that sort. That means the data cable from the PC's parport to the xylotex is only about 2 feet long, and it comes into the xylotex box on the opposite side from the output cables to the motors. I ran a piece of 12 gauge all around the xylotex board, connected to the data cables ground breakout, the psu's negative terminal, and to all the ground drain wires in the Star-Quad cables to the motors. I use a PMDX-106 running on a big wall wart to interface with the spindle motors controller, and all of that is jumpered via soldered joints back to this same piece of 12 gauge. There is no shielding on the spindle motor cabling, in fact I have an ammeter on 24" extension leads in series with the return wire right at the motor, and just made a run of 10 cartridge holding blocks (I'm also a handloader), 144 holes 1/2" each, or 112 5/8" holes, drilled most of the way through a piece of cleaned up 2x6 a foot or so long. The only gotcha was the bit got stuck and the z axis couldn't lift it to clear the chips. So the x axis pulled the top of one hole sideways about 50 thou. Out of well over 1000 holes. :) That and Porter Cables forstner style bits are dull as can be right out of the package, I cut spindle current by half just by sharpening it better. I did play with the peck increments, and probably should have used more cycles, but I wound up drilling half depth, clearing chips, then to 85%, clear chips, and a final push to 100% depth, in 3 cycles, in each case I could see the last 2% driving up the spindle current cuz the bit was stuffed full. >Just last week I had some problems when I used an unshielded cable >directly connected to my Mesa 5i20 board to the E-stop. This was a quick >hack to see if I could use EMC's E-stop input. When the spindle started >running, at specific speeds, the steppers started rattling randomly. >A friend of me bought a commercial (hobby type) CNC controller and he >had lots of problems in this same direction - in the end he replaced all >his cables and fitted opto couplers on all the I/O lines - now his >problems are gone. This I would do, if I ever have the problem. I have also probed for contour several times and have not had any errors of more than a thou or two in the data. This using the sliding tube opto-interrupter device one of the guys here gave me a link to when I asked about that a couple of years ago. Home- made of course. :) To repeat, all grounds are done in 'star' fashion with the motor drivers being at the center of the star, and no cable shielding connected except at the star. All machine grounds are through the 3rd pin, and all power on the same circuit to prevent lightning surges from being anything but 'longitudinal', meaning the whole system bounces in unison so there is not a surge because one part is plugged into wall circuit A, and the rest of it is plugged in on wall socket B which may be on the opposite leg of my 240 volt shop feed. When its all on one circuit, the whole thing can bounce 100KV measured from ground, but there isn't an inter unit surge since its all bouncing the same way, microsecond by microsecond. When dealing with multiple horsepower stuff, this isn't near as easy, and makes isolation transformers a lot more desirable. Piece of cake with my teeny stuff. :) >Regards, > > Rob -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If all the world's economists were laid end to end, we wouldn't reach a conclusion. -- William Baumol ------------------------------------------------------------------------------ Register Now & Save for Velocity, the Web Performance & Operations Conference from O'Reilly Media. Velocity features a full day of expert-led, hands-on workshops and two days of sessions from industry leaders in dedicated Performance & Operations tracks. Use code vel09scf and Save an extra 15% before 5/3. http://p.sf.net/sfu/velocityconf _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users