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X axis missing steps and skew

Discussion in 'Troubleshooting and Build Support' started by jkarnacki, Sep 20, 2011.

  1. jkarnacki

    jkarnacki Member

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    My machine has been running fine for a few months now but started acting up today. I can't be certain but it seems that it may have started after loading the new CNCUSB settings file (yes, I moved the switches on the board to ON). I only use my P3 once every couple weeks for whatever I happen to be working on - a new plane or maybe a liteply camera mount for fpv, and from what I remember everything was running smoothly. What I'm trying to say is that I don't use my P3 on a daily basis so it's hard to say when this problem started, maybe I just didn't notice it until now.

    My x axis is consistently missing steps. The foam sheet is always hanging out the front of the machine by 1/8" to 1/4". Even with the new rollers my foam (tried several different sheets of blue FFF) is consistently skewing and shifting to the right. It's enough missed steps and skew to the point where I can't even cut a usable full-fuse, botihng lines up.

    I've tried multiple belt tensions on the X stepper to no avail.

    I'm looking at a full-fuse I cut a couple weeks ago and it went together just fine (before the new settings file). I can't think of anything that's changed. My pulleys are seated tightly on the flat spots. Voltage on steppers are 2.7. Pressure rollers move freely.

    I can't figure this one out on my own!

    - Jeff
     
  2. kram242

    kram242 Administrator Staff Member

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    Hi Jeff,
    On your x axis do you have the metal pulley or the plastic one? This could be the cause of what appears to be missed steps when actually it may be the pulley slipping.
    As for the sudden skewing, this could be the fan fold itself. It seems that the thickness of fan fold from side to side is not consistent and one of the reasons we made the new guide system.Try a few test, draw a pencil mark on the side of the sheet where you are starting as a reference.
    Try jogging your fan fold sheet the length and then sending it home a few times, check the mark. Then flip the fanfold over and try it again. You should see a difference. Try this on a few different sheets and compare to find the best way to place the fanfold. If you have some posterboard try that and see how it compares. Posterboard has a nice even surface and seems to do better. I think the reason we see this sometimes and not other times is that each bundle/sheet is a little different with fanfold as well as depron. The new dual drive roller system of the Phlatprinter is much better at holding the sheet. So the accuracy of the the x axis depends on the quality of the sheet that is being used.
    I have been working with the new guides and they have corrected these problems with fanfold, they will not allow the fanfold to 'walk' no mater how inconsistent it is, it must stay where you set it and is forced to remain centered. Yesterday I completed a few of the latest versions of these guides and they will be available soon. The guides will be a big help in correcting the skew issues you are having.
    Please PM us about your pulley and we will help you further in correcting the slipping you are seeing on the x stepper.
    Thank you
    Mark and Trish
     
  3. jkarnacki

    jkarnacki Member

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    Thanks Mark, I'll look into what you suggest. The inconsistent thickness of fanfold from side to side may very well be the reason for the skew. That may be why my last plane came out fine - I was using real depron.

    I'll look at the pulley to see which one I have. At one point in time I had it cranked down pretty hard so I can't imagine it is slipping on the teeth, I guess I could Mark the belt and pulley with a sharpy and check that out. Either way I'll get back to you as to which style pulley I have.

    Gotta get all this figured out in time to test the hotwire attachment :D

    - Jeff
     
  4. jkarnacki

    jkarnacki Member

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    The X pulley I have has a black plastic gear and what looks to be a piece of aluminum next to it.

    I tried the same file (aircut) on a piece of 5 mm cellfoam (no waves, perfectly flat) and it returned exactly to zero! Maybe I'm not missing steps afterall. I would think that even with with wavy bluecor, it might skew but but only in a diagonal fashion if that makes sense. IIRC the whole sheet would end up hanging out the front of the flatprinter, not just one side. I'll have to try both of these tests again tomorrow to make sure it's not a fluke. Perhaps I can run the blucor skin side down and get better results as I think the waves are mostly on the unskinned side. I'll also try the test with the pencil mark.

    - Jeff
     
  5. dhc8guru

    dhc8guru Member

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    3/4" and 1" bluecore is the only DOW product I run in my machine. It will skew as much as a 1/2" running the full length and running a long program. Even with the thick blucore foam it is also wavy just not as bad as fan fold. When I run 6mm depron, there is no walking at all. I am looking forward to getting my hands on the new guides . Not only to help with skewing but also for consistantly lining up sheets of foam on production runs of parts.

    Something else I found helpfull with accuracy is to always make sure you are conventional milling on your tool paths and not climb milling. It doesnt matter when you use the grout bits but I use spiral flute bits and it makes a big difference of cut accuracy and the foam will not "burr" on the parts.
     
  6. jkarnacki

    jkarnacki Member

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    I just tried 200 inches of X movement on a sheet of depron and on a sheet of fanfold. The fanfold skewed a fraction of an inch but just barely - I'm not concerned about it. However, the depron sheet ended up sticking out the front of the machine by an 1/8" and the fanfold sheet was pushed into the machine by an 1/8".

    I've noticed that every time the X axis changes direction I hear a click noise immediately or shortly after the direction change. It's kind of a squeaking sound. I also tried tightening the belt but I still get the noise.

    So I guess my belt is slipping or I'm missing steps - I'm thinking the latter but I don't know why. I noticed my X stepper got pretty darn hot, I couldn't touch it for more than 4 or 5 seconds. Could the stepper still appear operational but have small glitches due to overheating? I'd hate to have to remove a stepper from a different axis just to test, I'd almost rather just order a "spare" :D

    - Jeff
     
  7. dhc8guru

    dhc8guru Member

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    Sounds to me like your driver card is getting ready to dump. Eventually it may come to the point of briefly driving the steppers then unlocking them followed by the steppers squealing. My second card started acting up in May but then worked fine till last month. If the problem gets worse, Shoot a temp gun at the voltage regulator on the driver board. You may see the temp on that regulator instantly jump from 100 to as high as 212. The regulator chip has three prongs and a heatsink bolted to it, connected to the board right next to the main chip and heatsink. At this time, I seem to be the only person experiencing this problem. Some people on cnc zone say this board has been know to have this problem and can sometimes be cured by removing the heatsink and reapplying some thermal paste to the chip and heat sink. Apparently the architecture of the board with the regulator and main chip so close together cause overheating issues. I don't know if it's true so take it for what it's worth.

    This was the thread posting my first issue with this board
    viewtopic.php?f=266&t=2394
     
  8. jkarnacki

    jkarnacki Member

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    Thanks dhc9guru. I don't have a temp gun but I'll try to find what you're talking about on the board and see how hot it gets.

    I had a problem with this board when I first got it. Mark and I couldn't figure it out so I ended up getting the USBCNC board and it fixed it. What was happening was that my x axis was only moving in one direction, no matter which way I told it to jog. I tried it on two different computers and none of the normal fixes worked. I even swapped steppers and the only way to get the x axis to work correctly was to add the usbcnc board. Mark and I were puzzled because it was the second board in a row that I had problems with, so we kinda discounted the fact that nobody is unlucky enough to get two consecutive bad boards :D

    - Jeff
     
  9. jkarnacki

    jkarnacki Member

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    Nope, the regulator and heat sinks on all axis actually stay quite cool.

    I'll actually get missed steps just from manually jogging some foam back and forth a few times. I line the foam up with the edge of the machine, set zero, then job back and forth a few times. Then I jog the x axis until cncusb software says X is at 0.00 yet the foam is either extending past the end of the machine or pushed in by about 1/8." I don't even have to jog it very far to happen. Seems like I'm missing steps in both directions. Tried bumping the V on X axis up to 3 but it didn't help.

    <EDIT>I just wired the X stepper motor to the Y axis on the driver board and what do you know - no missed steps. Maybe I'll try a different USB cable tomorrow. Otherwise it's looking like an issue with the mechatronics board or the usbcnc board, or the connection between the two.</EDIT>

    - Jeff
     
  10. TigerPilot

    TigerPilot Well-Known Member

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    Can you spell N E W C H I P? :D :D Bin there, done it, bought the T-shirt!!!
     
  11. Evil-Tunes

    Evil-Tunes Moderator Staff Member

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    :ROFL: :lol: :ROFL:
     
  12. dhc8guru

    dhc8guru Member

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    Is definitely the Mechtronics board. The temperature on the regulator chip won't always be overheating. In my case it ran cool but when I checked it when the failed axis stepper fully unlocked, that was when the temp shot through the roof.
    I am pretty sure more and more of these boards are going to surface with problems, its just a matter of how often and how hard you run it. Not saying all these boards are bad but I think a bad batch got out and the problems with them are just surfacing.

    Another thing I just read from oriental motor is the stepper should be run @ 2.2v ref. which I had been running 2.6V ref. Not that I think it would be the cause of the problem but good to know anyways.
     
  13. jkarnacki

    jkarnacki Member

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    ahahha this is good stuff :D

    Should I try swapping the chips under the heatsinks between X and Y to be positive or just go ahead and email easy-cnc for a new chip?

    - Jeff
     
  14. dhc8guru

    dhc8guru Member

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    I would talk to Mark. He will take care of you.
     
  15. jkarnacki

    jkarnacki Member

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    Ordered 620-1144-1-ND from digikey. Let's hope this is the fix! :)

    - Jeff
     
  16. dhc8guru

    dhc8guru Member

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    Cool! Hope that will take care of it.
    I just got my probotix setup running tonight. Wow! Even before my easy CNC driver card melted down it didn't run as accurate as the probotix set up. Running the steppers in unipolar is much quieter and smoother. Keeping my fingers crossed it keeps running this good.
     
  17. TigerPilot

    TigerPilot Well-Known Member

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    I don't have the number with me, I'm on vacation in the Dom. Rep., but did you make sure it's the high temp chip?
     
  18. jkarnacki

    jkarnacki Member

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    yea it's the high temp version. one chip was rated with an operating voltage of 25-80 degrees but I got the one that went up to 125 (IIRC).

    - Jeff
     
  19. jkarnacki

    jkarnacki Member

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    Testing the new chip right now. I should know in a few minutes if it solved the problem. :)

    - Jeff
     
  20. jkarnacki

    jkarnacki Member

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    X is coming back within .02 now. I'm happy with that. Might be some backlash but I'm not gonna fiddle with that yet. I don't have anything to cut yet but when I do that will be the real test.

    - Jeff
     
  21. rcav8r

    rcav8r Moderator Staff Member

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    Knock on foam, my card has been rock solid, and I have one of the original ones... Where are you guys getting your chips? Maybe I should get a spare....that way I won't need it.
     
  22. dhc8guru

    dhc8guru Member

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    I also am running off about .020 on the X axis only right now. I think its actually due to having a slight bump in the grip tape at the seam on one of my rollers.

    When you put the chip in, did you use some thermal paste on the heatsink?
     
  23. jkarnacki

    jkarnacki Member

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    No thermal paste, I just reused the double sided tape that was there. Should I pick up some thermal paste? It doesn't get warm at all...

    I just tried cutting two fuse sides out and they are still awful. It's coming back pretty much to zero, though. I double checked my calibration and it's spot on. I can line the tabs on one side of the fuse up fine but then the other side is 3/16" off. My gantry is pretty tight, the y belt will move about 1/16" with firm pressure

    Any ideas? This stuff is so elusive :)

    - Jeff
     
  24. dhc8guru

    dhc8guru Member

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    The double sick tape is actually a thermal conductive tape. So no worries if you were able to reuse it.
    I have no solution for you on the cut accuracy. Sorry
     
  25. TigerPilot

    TigerPilot Well-Known Member

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    Jeff, I take it that the 3/16" problem is on the x-axis. You have backlash error of 0.02 which is almost 1/32". Go back and forth a few times and it can add up.

    On the other hand, I know many say that they run at high ipm's. I found that I get round corners at anything above 60ipm. Even in foam. I have to cut everything at low speed. Maybe that is your problem too?
     

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