On Monday 24 November 2008, Andrew Ayre wrote: >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 later dremels have an elastomer seat cushion for the spindle nose bearing, and its rather loosely coupled to the motor shaft itself. Another friend made a new alu nosepiece with a precision seat for that bearing for his dremel and it works much much better. Also, the last one I bought had a seriously defective 1/8" collet, it allowed, and demanded, about a 20 thou runout. I spotted a card of collets at Lowes, and a new one runs nicely. There is, and I forgotten the name, a german maker of such goodies that is very highly thought of, maybe someone will chime in with more details. I believe its about the same diameter as the dremel, but an inch or so longer. I looked at that machine some time back and came to the conclusion it was a 6 month machine. MDF warps over time when weight is applied, so I'd think it would be hard put to maintain a flat bed over time. And 12x18x3 won't carve a gunstock, so I didn't persue it any farther. That would need 12x48x10 and an A-B axis, the A to turn the stock on the x axis, the B to tilt the head along the x axis so it could reach into stuff like thumbholes, which I'm partial to. A is easy enough, but the B is a whole new design of the gantry itself, which would gain considerable weight in the process. I have a mental picture but haven't tried to draw it up in a CAD proggy yet. > >I've recently purchased a dedicated PC for EMC2 and I now have 2.2.7 >running as of today. Great! Does it still do it? >>> 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-c >ompensation/ > >>> 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. Well, your 'head' isn't nearly a heavy as mine. With mine, the whole thing slides up and down a column that is (IMO) too slender, on a way sled that really needs to be at least twice as long for good guidance. I'm probably pushing 25 pounds up and down. But .0003"? That's almost magic unless its a ball screw, preloaded to boot. Anyway, it sounds like you are making progress, Andy, which is good. -- 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) Bombeck's Rule of Medicine: Never go to a doctor whose office plants have died. ------------------------------------------------------------------------- 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
