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olivierc

Help: one axis starts shifting in middle of print

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Hi, I need you guys help because I have no idea what's going on. I have read about objects printing completely sideway because of badly tightened parts, but here its different.

I was printing a big model, cura predicted a 30 hours print. It printed well for over 10 hours. But then out of nowhere, the layers started to shift to the left, badly, like several millimeter offset for each new layer. The layers themselves seems they would have been printed correctly, but at the wrong place, like the head did not position correctly at the beginning of each new layer.

I immediately stopped the print of course. I then checked the printer, pulleys, belts, axis... everything looks normal, I don't see what could have failed. I did a quick test cube after that and it printed fine. Could it be the gcode? I used cura 13.05.2 beta

The reason I'm really clueless is that it happened suddenly and not progressively, and that I can't find anything wrong with the hardware

I attached some photos so you can see for yourself

badprint01.jpg

badprint_outline.jpg

badprint02.jpg

 

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You're most likely skipping steps on fast travel moves. In the x direction, certain fast moves are failing to happen, causing the head to lose track of its position.

I'd check how easily the head slides around by hand in y and, especially, x directions. If there are any tight spots, or x is generally tighter than y, then make sure everything is square, and apply sewing machine oil to the rods.

The infill pattern looks pretty rough - extra resistance from catching a blob might indeed have triggered a skip. The other thing you might look at is checking your acceleration speed: the more recent default of 5000mm/s2 seems to cause problems in some set ups. I'd try lowering that to 3000.

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Thank you for the detailed answered illuminarti. the infill looks rough because of those last three or four layers that are all over the place, it looked much nicer before, all perfectly aligned. I had cleaned and oiled the axes just before starting this print, since it was a long one.

I don't have any problem sliding the X and Y manually. There is a bit of resistance overall, but I can't tell if it's right, maybe the belts are a bit too tight. I can't feel any difference between X and Y

I will try to build a custom version of mariln with the setting you recommend, I have always been using the default one, I have not upgraded since april.

 

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First of all I would make darn sure none of the pulleys are slipping by using a sharpie and marking very tiny precise marks on the pulley and shaft. This is an extremely common problem. Mark all 6 pulleys and shafts. The one on the motor itself is going to be tough though - not sure how to do that - maybe just tighten it more? The UM kit comes with extra set screws as the ones that come with the pulleys aren't as good. Consider changing the motor with this one. Tighten the hell out of all 6 pulleys.

The second most common problem is that the short belt (to the motor) for the X axis may be rubbing the back wood piece of the UM. Especially if you used the black plastic spacers instead of the wooden motor mount. You can quickly diagnose this issue because during printing, if you look at the X motor short belt you will see it twisting one way when the head moves left and then twist another way when the head moves right. If you have that problem then this is most surely the problem. Add washers as spacers on the motor mounts.

Another likely problem is that you got a new Marlin firmware installed and your new default accelerations changed from 3000 (the old default) to 5000 (the new default). You can check this on your UM or add an acceleration parameter to your "start gcode" settings in Cura.

The least likely problem is not enough lubrication but it sounds like you took care of that. But still, check how the x axis feels manually when you move the head left and right in the general area of all 4 corners.

To test if the problem is fixed it might be best to take your existing "bad gcode model" and remove the bottom inch or so of layers so you can skip right to the "bad" layers where the acceleration is too high for you UM. You don't necessarily need to have filament in your machine to test it. Or after it starts printing in air you can override your z stepper by forcing the z coupler to move the bed back up. Or you can place something (maybe the bad print? A stack of paper?) onto the bed and let it print on that.

 

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First of all I would make darn sure none of the pulleys are slipping by using a sharpie

Alright, I feel stupid I was just coming just to say that I found my problem, when I saw your message. it was inteed a pulley, but the one on the stepper, the only one I forgot to check. I always check the ones on the axis because they get loose more often, but I forgot to check those two.

I'm very sorry for wasting your time with something that stupid. It's not the first time I get a loosen pulley, it was the first thing I checked, but missed that one.

The funny thing is that I still manage to print a couple of test cubes that looked ok., it's only when I tried something bigger that I saw it happening again.

 

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Yes! that's what I got! I just need the rods, I tried to order from conrad like you suggested but my visa payment could not go through, because the shipping address is in belgium while the address attached to the card is in france. Some sites do these kind of security check. I must ask some co-worker to order it for me but keep forgetting

 

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Olivierc,

Did tightening the pulleys ever solve that shifting issue you were having? We've got an utli-2 extended that's been having the same issue, despite our IT guys saying it's been fixed, now several times... It's happened on a few different prints, and a few different times. We've also checked the files, and there aren't any geometry issues with them either..

I realize this post was from a while ago, but I'm not really seeing anything current with the same/similar issues.

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Hi, SciRefDesk,

If you're having shifting prints, it's most often caused by a loose set screw, either in the pulleys on your axis rods, or on the motor itself. Are your shifts left to right or front and back?

Also, is your XY axis well-lubricated? Does the printhead move freely if you try to move it by hand with the machine powered off?

Use the 2mm allen key that came with your printer to check all the set screws in the rods on the pulleys and make sure they're tight. If they are, go ahead and try to home your head with Maintenance --> Advanced --> Home Head. It should home to the back left corner. Once it gets there, it should be locked in place. Try to move it forward, and try to move it to right. If you can move it in either direction when the motor is locked in place, then the pulley on the motor itself is loose (or the pulley attached to the short belt on the rod for the X motor). There are instructions here for accessing the motor pulley to tighten it.

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Hi, SciRefDesk,

If you're having shifting prints, it's most often caused by a loose set screw, either in the pulleys on your axis rods, or on the motor itself. Are your shifts left to right or front and back?

Also, is your XY axis well-lubricated? Does the printhead move freely if you try to move it by hand with the machine powered off?

Use the 2mm allen key that came with your printer to check all the set screws in the rods on the pulleys and make sure they're tight. If they are, go ahead and try to home your head with Maintenance --> Advanced --> Home Head. It should home to the back left corner. Once it gets there, it should be locked in place. Try to move it forward, and try to move it to right. If you can move it in either direction when the motor is locked in place, then the pulley on the motor itself is loose (or the pulley attached to the short belt on the rod for the X motor). There are instructions here for accessing the motor pulley to tighten it.

 

Hey thanks, for the suggestions. The printer is for student use in a university library, so we have an IT department that handles all the maintenance for it. Because of it, we're not really allowed to check all that stuff ourselves, I just wanted to see if that's what fixed the original poster's question/issue.

As far as I can tell everything is well lubricated, and the print head does move fairly easily when the machine is off. The shifts are occurring left to right, pretty much exclusively. Could there be any software issues causing this? Since we got the printer we were using the 15.06.03 beta version, and weren't having any issues. Sometime in the recent weeks though we switched to the 2.1.1 64 bit beta, but the shifting wasn't really occurring when we switched versions.

Thanks for the help.

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I haven't tested the Beta enough yet to know if there are issues with it, but this is the first I've heard of shifting related to the beta switch. If the motor is getting too much current you can sometimes see a hard shift in the print, or if the machine is over heating. When the firmware was updated, was a factory reset performed? If not, I recommend it.

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There are instructions here for accessing the motor pulley to tighten it.

I haven't been here for a while. I just wanted to post a thank you for this link. I was getting severe slipping on the y-axis, but only with some prints. I had checked all the accessible pulleys, I couldn't reach the ones on the motor itself.

The main thing that made the difference was that gem about using homing the print head and seeing if I can move it. I could! Without that certainty I'd have been reluctant to start taking things apart to reach the motor.

And, so far it is printing perfectly - after about 6 failed attempts.

On the bright side - I tuned a lot of things trying to debug this, so now it's working as good as ever!

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There are instructions here for accessing the motor pulley to tighten it.

I haven't been here for a while. I just wanted to post a thank you for this link. I was getting severe slipping on the y-axis, but only with some prints. I had checked all the accessible pulleys, I couldn't reach the ones on the motor itself.

The main thing that made the difference was that gem about using homing the print head and seeing if I can move it. I could! Without that certainty I'd have been reluctant to start taking things apart to reach the motor.

And, so far it is printing perfectly - after about 6 failed attempts.

On the bright side - I tuned a lot of things trying to debug this, so now it's working as good as ever!

Glad to help! And extra glad to hear your printer is back up and running as it should. Trying to move the locked printhead is always a favorite test of mine, because it's a good way to know if it's loose before taking anything apart.

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