Print keeps shifting

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GQQSER
Posts: 20
Joined: Tue Apr 24, 2018 8:41 pm

Print keeps shifting

Postby GQQSER » Tue Jun 12, 2018 2:01 pm

I am running into this problem on my last two prints. About halfway through the build, the print seems to be shifting coordinates. At first I thought that maybe the nozzle had caught on the build itself and shifted the print. I realized quickly however, that the base of the print was still attached to the buildtak and was in the same place it started. I further observed the clips and print surface were in the original position, indicating that it had not moved.
The fist print shifted approximately 15mm to the south ( if you are standing in front of the door of the raise3d N2 plus the south would be towards the door) for no apprent reason and happened much later in the print about 90% complete. The second one was approximately 100mm to the east and happened a little less than halfway through the build.
I thought if might be a corrupt .stl file that caused this, so I completely redrew the piece and exported to ideamaker and sliced. I double checked all the setting from previous successful builds to make sure nothing had changed.

I am out of ideas. I would very much appreciate hearing about anything else I may have missed, or a solution would be great.
Bad Print.jpg

Jetguy
Posts: 2700
Joined: Tue Mar 22, 2016 1:40 am
Location: In a van, down by the river

Re: Print keeps shifting

Postby Jetguy » Tue Jun 12, 2018 3:46 pm

Dual or single extruder printer?
You had 2 different shifts, X and Y axis, so this is highly unlikely to be code or a specific axis based mechanical failure.
Which leads to this statement sadly likely incorrect. "At first I thought that maybe the nozzle had caught on the build itself and shifted the print"

There is no position feedback in a typical 3D printer. It is an open loop (no position feedback) system. The controller sends the step and direction command pulses to the stepper driver, the stepper driver steps through the coil commutation and current level setting, the coils in the motor follow that logical field rotation and you the user ASSUMES the rotor follows that rotation and millions of moves or "steps" during a print. Anytime the friction, a nozzle striking curled up print layers, or dozens of other reasons, the basic idea is the force on the axis exceeds the motor torque, the motor "skips a step" and moves to the next logical pole alignment thus shifting all coordinates after the skipped step. With no feedback, the system has no clue a mistake has happened.

The only thing you as a user can do is:
Ensure your axis moves freely- no binding, misalignment or other mechanical drag.

Ensure the motor to shaft coupler is not broken- highly unlikely in this case, especially since the shift happened in one print on X and one print on Y. Again, this is highly unlikely, your failures are very different from the typical results of this type of very specific mechanical issue, but at least know about it and understand it.

Ensure if running a dual extruder, the nozzles are properly set to the exact sub mm same height, or that the unused nozzle/hotend is removed or raised so it's impossible for it to catch the print

Properly calibrate filament diameter and extrusion multiplier to prevent over extrusion and the nozzles needing to plow through over extruded big flat layers.

Ensure extrusion temperature and general ambient temp, cooling, and dozens of other factors so that the layers do not tend to curl up, thus resulting in a nozzle strike. Again, as a note, dual extruder equiped N series are known to have less than perfect layer cooling do to the lack of a dedicated layer cooling fan. This is different than the cooling fans being used to cool the heatsinks on the hotends (although that is a dual purpose fan).

GQQSER
Posts: 20
Joined: Tue Apr 24, 2018 8:41 pm

Re: Print keeps shifting

Postby GQQSER » Tue Jun 12, 2018 7:24 pm

Thanks Jetguy, I have since ran several small but complex prints, all successfully. What I took away from your comments is that it was most likely and interference between nozzle and build. I am definitely leaning that way. I do not quite understand your comments

I will look into how to properly calibrate filament diameter and extrusion multiplier, as I am not familiar with these functions or terms.

Thank you for your time in this matter, it was very kind of you.

Edit: I get what you speaking about, I was looking in the advanced section in the Ideamaker 3.1.7, its actually found on the front page where you select the template. I didn't realize that I had to mic the filament and change this value every time.

Vice Chief
Posts: 88
Joined: Wed Aug 23, 2017 5:04 am
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Re: Print keeps shifting

Postby Vice Chief » Tue Jun 12, 2018 8:32 pm

You don't have to, but you will get better results as a general rule. I only check filament when it's acting up.

I've had similar problems to yours once or twice. The first time, it was a nozzle strike. The other times, my limit switch was mashed (I know this seems improbable). Poke your head in the build chamber and be sure your switches are in place.

Jetguy
Posts: 2700
Joined: Tue Mar 22, 2016 1:40 am
Location: In a van, down by the river

Re: Print keeps shifting

Postby Jetguy » Tue Jun 12, 2018 8:48 pm

Limit switches only affect homing. The firmware completely ignores them during the print.
Yes, other brands of printers, other firmwares, a limit switch can trigger a skip, on our firmware, this is ignored.

Vice Chief
Posts: 88
Joined: Wed Aug 23, 2017 5:04 am
Contact:

Re: Print keeps shifting

Postby Vice Chief » Tue Jun 12, 2018 9:28 pm

I know it seems implausible and is probably not the case here. Just to explain a little further, I had a large print which failed in the way pictured (shift of some kind). At some point during the print process, the print head mashed the heck out of the limit switch. Every print after that was showing up in the wrong place on the bed and failing with a huge birds nest (I wasn't always around for the beginning of the print). The reason was that the homing switch was stuck in the "on" position, so wherever the print head was, it would assume it was zeroed in that axis. Just saying, if you have an error like this, especially on large prints, it's good practice to check your limit switches. Again, doubt it's the problem here.

RogerSt
Posts: 40
Joined: Mon Mar 21, 2016 12:24 pm

Re: Print keeps shifting

Postby RogerSt » Wed Jun 13, 2018 4:24 am

I had the same problem.
In my case a broken clutch at the X axis stepper motor was the problem.
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GQQSER
Posts: 20
Joined: Tue Apr 24, 2018 8:41 pm

Re: Print keeps shifting

Postby GQQSER » Wed Jun 13, 2018 9:10 pm

These are all awesome "be aware" items. It seems as soon as I think I have this down pat, there's another setting I didn't think of. Thanks everyone for helping me out. I am now gauging the filament each time I print and making adjustments accordingly. So far so good, but I haven't made a large print yet.


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