Print suddenly became longer in the Y Axis? **Solved**



  • I was printing a TPU Tyre for an OpenRC build and suddenly it started printing longer in the Y Axis. I let it finish as at the time it looked like a minor layer shift but it actually started printing very consistently larger and slightly offset in the Y axis.

    After checking the mechanics over I have it another shot only to find the 2nd wheel was entirely longer in the Y axis with no signs of layer shifting!

    I figure if it was just layer shifting or slipping belts then it should actually shift in one direction and/or get smaller, not longer? But this seems to be a very consistent increase of about 2-3% size in the Y Axis alone. So now I’m wondering if it’s a possible software or electronics issue.

    I’ll keep looking for mechanical faults as I still think it’s most likely that but has anyone experienced something like this before?

    Using a DuetWifi on firmware 1.21

    I've added some pictures for reference
    SideView
    TopViewOval
    BottomViewRound


  • administrators

    Which is the correct size, the lower or the upper part of the wheel? A loose pulley may have made the lower part smaller than it should be.



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  • @dc42 The correct size is the lower part (circular) rather then the upper part (oval) which is why I'm confused by the issue - every mechanical issue I've had in the past, like loose belts has resulted in smaller prints or shifted prints, not consistently larger (in one axis)?

    I have checked the belts though and they're pretty tight - will try run some test prints tonight.

    @Catalin_RO Did you start responded in the wrong post?



  • I have removed my previous messages. In the end it was a problem of the CAM software, combined with the maximum allowed jerk on X and Y. The default configuration specified 900mm/min, probably pretty much OK for a 3D printer, but way too much for a CNC machine. In my case just the milling spindle with mount exceeds 2kg and there are 2kg from X and Z steppers. Combined with cables, cable chains, Al endplates and V-slot profiles, surely the whole gantry has in excess of 10kg.

    Doing and "air cut" (spindle stopped, cutting tool way above the raw material) I could actually hear the problem and then I looked much deeper into the CAM software to find unexpected sudden direction changes. I reduced the maximum jerk to 300mm/min.

    But among other things, I have also tried cutting the Al piece by using straight lines instead of arcs, though pretty small ones. The same problem was visible immediately. On larger details everything was OK while on finer ones I could hear the steppers fighting with the gantry. I presume that you tire also has a lot of fine details, especially in volume filling regions. And it happens after a certain height. Maybe the slicer decided to add some extra artifacts from there on and got the controller in the same situation as my CNC router.

    Could you try with the same file after reducing maximum jerk to 30-40% of the current value?


  • administrators

    @hobsie Assuming you have a Cartesian machine, then yes it is normal for a loose drive pulley to result in shorter not longer movements.

    In the firmware the only command that would trigger this is as a feature is M556, presumably you have not got M556 in your gcode? (Highly unlikely but worth asking!). Other firmware changes that might result in this would be incorrect steps/mm on that axis (once again I assume you do not have a M92 somewhere in the print file!

    The thing that gets me as confusing is you next print was 100% expanded on the Y axis. can you try some long moves on that axis and measure the commanded move vs the actual move.



  • @t3p3tony cheers for the response - Yeah I should have probably mention that I do have a cartesian setup (P3SteelXL, basically a very heavy Prusa i3) finally got the kids to bed so I'm going to try some calibration prints. Not seeing M556 or M92 in the code file itself and steps/mm for both X/Y are the same value of 100 for M92 in the config.g (GT2 Belts, 16 tooth pulleys, 1.8 degree motors and the default 16 microstep)

    I've taken some calliper measurements of the tyres since I realised I didn't actually know how elongated in the YAxis the model became.

    • 1st wheel I printed (which came out perfectly) I get ~56.5mm diameter
    • 2nd wheel (which shifted to the elongated Y about 2/3 of the way through the print) I get ~56.5mm diameter for the first 2/3 and then ~56.5mm in the X and ~58.5 in the Y
    • 3rd wheel (which is elongated in Y for the entire wheel) I get the same measurements as the last third of the 2nd wheel (i.e. 56.5X 58.5Y)

    I'll let you know how my calibration prints come out!



  • Alright first calibration print done.

    Ignore the horrible over extrusion on the lower layers!

    100x100mm square came out as

    100.00mm in the X and 104.02mm in the Y which roughly matches up with the measurements I took of the wheels.

    XAxis
    XAxis

    YAxis
    YAxis

    I'm going to clean the printer up a bit and try Prusa's Slic3r (prints so far have been sliced with Cura) to rule that out as well.

    Edit (23:04): Same result with Slic3r (although it did a much better job with flow control on the bottom layer solid infills) 100X by 104Y mm.


  • administrators

    Try moving the axis on Y using the jog buttons to see if 100mm of commanded movement = 100mm of actual movement.



  • I recently had a similar problem on the Y axis of my Anet A6 that I still use sometimes.

    Problem was the cheap belt included in the kit.
    It had stretched... maybe because of over tightening and the heat of the heatbed above.
    And I think that happened pretty suddenly within a short time span and not just over time...

    Well, and I had an other problem where I dripped hot glue on the pulley of the X axis and didn't notice it... it was just a tiny amount and barely visible, but was enough to increase the effective diameter (unevenly).

    Like @t3p3tony, I would also suggest to test by moving the axis and to measure the actual moved distance, maybe also in e.g. 10mm steps to see if the error is conststent or not.



  • Looks like my post last night didn't go through before the forum went down for a bit?

    Anyway I tried another print after changing the steps per mm in the Y from 100 to 100/104 (~96) and got a perfect 100x100mm test print - I suppose that's a working solution.

    @hurzhurz I did change my belts to a metal core GT2 a few weeks ago but have done maybe a dozen prints without issue and the heated bed was actually off for the print when things went wrong (since I'd never get the TPU print off of my PEI if it was on!) - but that's a good place for me to check. I did notice a bit of dirt on the belt where it engages with the pulley (it's a white belt so it's easy to spot) so who knows, maybe the teeth on the belt have slipped?!

    In the office atm so i'll check again tonight.

    Thanks for everyone's input so far.



  • @hurzhurz @T3P3Tony

    Thanks for you help guys, we have a winner!

    My new tough metal core belt turns out to be not so tough and must have softened (probably from friction/heat) at some point and has actually stretched in the area over the toothed pulley.

    I checked the movement as @T3P3Tony suggested and it was elongated near the centre of the bed's Y axis but not towards the edges. After @hurzhurz mentioned his issue with his Anet belts I then went and checked the belt and found this:

    You can actually see where the rubber has stretched and increased distance between the belt's teeth!
    1_1526505638955_IMG_8061.JPG 0_1526505638954_IMG_2835.JPG

    Thanks again for everyone's help - turned out to not be a duet related issue at all but you guys got me looking in the right place.



  • I can't find the link right now, but it clearly gave information that the minimum turn radius for steel-corded GT2 belts was larger than even 20-tooth pulleys. Consequently, the thin cords work harden and snap, allowing the rubber to stretch.



  • @plasticmetal had I seen that advice before I might have been able to avoid this whole thing!

    I suspect that’s what has happened, pulling the belt apart in my hands it snapped pretty easily at the point where it was engaging with the pulley while the rest of it was still pretty solid.

    I had some spare rubber belts so I’ve gone back to those and all seems to work well again.



  • I tried some of the white steel core belt for a while on my coreXY and that lasted for about a week. The belts felt spongy and didn't appear to be very good quality despite being more expensive. I swapped them out for normal belt again before anything went really wrong, but I could tell that something was bound to. Now I'm waiting for some genuine Gates belts.


  • administrators

    @hobsie Belts with an aramid fiber or equivalent in are the best (like the gates ones) as they can handle the turn radius but also do not stretch (as some of the cheaper belts do.

    P.S. glad you got it working!



  • @phaedrux : where did you find genuine gates belts online (at least an European source...)


 

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