Unwanted Y axis offset

  • Over the past 5 months I have been building up a reprap delta using a duet wifi, nema 17 motors, an e3d lite6 hotend, and a heated aluminium plate as the print bed. after some trials and tribulations, we got accurate bed probing, and ran auto calibration until the deviation was 0.0036 over 0.0006, then mesh bed leveling to get a good first layer, but we have some unusual print artifacts.
    when we run a print, the layers shift towards the front of the print bed, away from the y axis stepper, at about 0.2 mm per layer. in order to rectify this i've tried switching out the sprung tensioners for 3d printed ones, manually leveling the bed and checking the wiring, but there has been no change.
    On some print the offset is only in the first 35 or so layers, then it straightens out, on other prints (https://www.thingiverse.com/thing:36321) the base is skewed, but the central shaft is fine, then the top cuppy bit is offset.
    Any ideas?

    EDIT: if print footage is needed, you can find some at twitch.tv/hassa1293
    EDIT 2: my material of choice is colorfabb ngen, but the issue has persisted with everything from PLA, to Nylon and even flexibles

  • administrators

    Someone else reported a related similar symptom several weeks ago in these forums. There was gradual later shifting which stopped after a certain height. My recollection is that it was caused by using steel-cored belts, and the small pulley diameter had caused the steel core to fracture in a section of the belt.

  • i used cheap ebay gt2 belt, which is fiber reinforced rubber, and 20t pulleys, Also my design makes switching belts completely maddening, and so it's something i'd really like to avoid, i thing it's something to do with travel moves, as vase mode prints are fine, but conventional hollow prints show the shift turning down acceleration didn't do much, but do you have any other ideas?

  • administrators

    What acceleration and jerk settings are you using? Also, what is the specification of your stepper motors, and what current do you run them at?

  • I used the stock reprapfirmware configurator numbers, acceleration is at 1000 mm/s^2, jerk is 1200mm/min, steppers are run at 1A, and they are rated for 1.8A , they are 1.8 steppers at 49Ncm torque

  • administrators

    You could try reducing jerk to 600 and increase current to 1200 or 1300mA.

  • I applied those changes, then printed a 10x10x100mm tower, There is a very slight tilt toward negative y, and there are a few blemishes at 30mm , and especially at 85mm where there is a far sharper transition

  • Fixed it, I forgot to install a set screw in the y axis motor, fixed it, and i'm waiting for a print to confirm that was the problem

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