Gene Heskett wrote: > On Saturday 22 November 2008, Andrew Ayre wrote: >> Gene Heskett wrote: >>> On Saturday 22 November 2008, Andrew Ayre wrote: >>>> Jon Elson wrote: >>>>> Andrew Ayre wrote: >>>>>> Hi, I've been happily generating g-code files and cutting them with >>>>>> AXIS. I'm using EMC2 pre-2.2 CVS HEAD. Yes, I know it's old but I have >>>>>> everything working and I am reluctant to change it right now as I am >>>>>> trying to get Christmas gifts made as quickly as possible. >>>>>> >>>>>> With a new g-code file I get "Joint 0 Following Error" at the same >>>>>> point every time in the file. Line 161 I believe. The g-code file is >>>>>> here: >>>>>> >>>>>> http://files.britishideas.com/public/emc2/jointerror1.ngc >>>>>> >>>>>> On April 17th, 2007 Chris Radek said this about the error message: >>>>>> >>>>>> "It means the difference between the commanded position and feedback >>>>>> position differ by more than the allowed following error." >>>>>> >>>>>> I am using a simple, HobbyCNC card with steppers, three axis, no >>>>>> feedback. I have backlash compensation set in the emc2 ini file. I have >>>>>> cut lots of g-code files without a problem until now. Can anyone give >>>>>> me some hints on how to solve this? Is it a problem with the g-code? >>>>> A following error in this case means that the commanded velocity >>>>> required more steps/second than the step generator could produce, with >>>>> the settings of your system. It may be possible to make the step >>>>> generator run faster by decreasing the value of BASE_PERIOD in the >>>>> [EMCMOT] section of your .ini file. Warning! If you make this value >>>>> too small, your system will freeze up when you start EMC. A quick check >>>>> would be to set your feed override to 50% and see if the program gets >>>>> past this spot. I didn't see anything near line 161 that looked like a >>>>> sudden fast and long move. I do notice some G00 moves at other spots, >>>>> which would command the fastest motion permitted by the .ini file >>>>> parameters. That would be where I'd expect to see a following error. A >>>>> 50% feed override ALSO affects G00 moves, so all motion should slow to >>>>> 50%, and it should get past the bad spot. If it is really tripping on a >>>>> G00 move, then you need to lower the MAX velocity in your .ini file >>>>> (unless speeding up the BASE_PERIOD is possible.) >>>> Thanks for the detailed reply. I set the feed override to 44% and it >>>> works (slowly), but I would like to better understand this so I can >>>> avoid this in the future. >>>> >>>> I've set the BASE_PERIOD based on the latency test, and it is the >>>> maximum my machine can run at. It gives me a max speed of 71.6 IPM. I >>>> can't decrease this value, unfortunately. >>> And why not? All it takes is an editor to change that value in the .ini >>> file, it is in (I think) nanoseconds, and a 25% upward increment should >>> still work just fine if your limit is 30 ipm. For steppers though, 30 ipm >>> is pushing them, and torque at that speed, unless you have lots higher >>> voltages available than I, is going to be well below the motors rated >>> value. >> I meant decrease the BASE_PERIOD. Sorry if what I wrote was confusing. >> >> My steppers have a max torque of 305 oz-in at 3A and I am running them >> at 2A (36VDC input I believe). Do you know of a formula or graph that >> allows me to work out the optimal cutting speed for the most torque? My >> machine is quite small - 18" x 12" x 3" cutting area. I assumed the >> motors I have are overkill for this size of machine (when cutting wood), >> but maybe that is wrong? > > Chuckle, bigger than mine. Gantry style? If I had room to play, I cvould be > tempted to do one, about an 12x48 work area, with an A axis to turn stock > blanks as they art carved. :) As far as overkill, no, its never overkill > till the machine can't support the weight of them. :)
Yes, gantry style. See: www.fireballcnc.com. > 30 ipm is going to be down the far side of the torque curve. Particularly if > carving wood, whose dust can raise the friction of the movements pretty > badly. I've had my micromill seize up and stall at 8 ipm after using it to > do a couple dozen 3/8" x 1.5" x .8" deep mortises in cherry. Sure does make > neat mortises though when using an 1/8" upcut carbide mill. :) I'm also using a 1/8" upcut carbide mill. Seems to lose performance after around 5000 - 6000 inches. I guess that is normal... don't really have the experience to be sure. Perhaps I am doing something to dull the bit quickly? The nice thing about the FireballCNC machine is that if a hard limit is reached the motors just stall with no damage to the machine. >> 30 IPM is an arbitrary value that I picked that I didn't feel >> comfortable going above. If I knew I could run it faster I would, but >> I'm just starting out. > > One of the problems that pushes the speed up is that the cuttings are part of > the bit cooling, they carry away the heat. Cut too thin (on either edge) and > the bits get hot too fast. If you are seeing burns, slow the bit rpms down, > speed up the move, or replace the bit, its getting dull. This is an area I am still completely unsure about. I get chatter and nothing I seem to do helps. I've tried slowing the spindle down, increasing the feedrate, slowing the feedrate, etc. I guess it is slight runout in the spindle. >>>> The g-code file is supposed to limit the speed to 30 IPM, and you can >>>> see this when running the file in AXIS. >>>> >>>> However I now notice that when the file is running in AXIS the velocity >>>> occasionally and only for a split second displays a value of 71.6 IPM. >>>> This raises two questions for me: >>>> >>>> - why would a movement cause the velocity to go beyond the maximum of >>>> 30 IPM that I set? Is that a problem with AXIS/EMC2 or the g-code? >>> What version of emc, and what backlash settings please? >> pre-2.2 CVS HEAD. The backlash settings are: >> > You may want to update that. Someplace in about that time frame I believe > the > backlash handling was changed to put them under the control of the MAXVEL and > MAX_ACCEL settings, where prior versions did them as fast as possible, which > led to following errors at direction reversals for me if the backlash setting > exceeded the max error. It also caused lost steps. It doesn't do that now > for a while. I've recently purchased a dedicated PC for EMC2 and I now have 2.2.7 running as of today. >> X: 0.005375" > > This could be adjust down I'd think. Wear? Not sure what you mean. It seemed to help quite a bit. See: http://www.britishideas.com/2008/06/19/measuring-cnc-backlash-and-software-compensation/ >> Y: 0.0025" >> Z: 0.0003" > > Head weight is the preload? Not always realistic when pushing on a drill bit > to bore a hole. The hole won't be quite as deep as you told emc to do in > that case. Sorry, I don't know what "head weight is the preload" means. I'm still very new to this and I'm sure I'm doing a million things wrong. Andy -- Andy PGP Key ID: 0xDC1B5864 ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
