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COREXY layer shift

Posted by DapDeveloper 
COREXY layer shift
August 02, 2017 04:50AM
Hi,
I have built a 3D Printer based on CoreXY system.
I tried to print some test models , like cubes, cylinders, etc. and all models are right, but when i tried to print a more complex model i noticed a layer shift at 45° degress.
The left model is printed with the same printer but layer height 0.3 , the right model with layer height 0.1.

Any ideas?
Thanks.

Edited 1 time(s). Last edit at 08/02/2017 05:00AM by DapDeveloper.
Attachments:
open | download - err2.png (549.7 KB)
Re: COREXY layer shift
August 02, 2017 05:13AM
Because it only happens with the 0.1 mm print and because it is so "straight" (and not semi random) I have the feeling we can rule out hardware problems - except maybe a slight underpowering of the motor which would make it skip a step only in very extreme conditions (change of direction and speed).

So try to give a little more current to the motor ?

If that doesn't help, you might have to tune some fine settings in your firmware (jerk and acceleration comes to mind) or in your slicer software (some have options to avoid "overshaking" movements).


Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.
Re: COREXY layer shift
August 02, 2017 06:21AM
Hi,
thanks for the answer.
I tried to change the motors,the board and the drivers, nothing change.
I also tried to cut the model in two parts to print only the upper , and the result is good (no shift layer).
The main difference between the two files are:

1. The dimension of the file (quantity of informations)
2. Printing time

I just tried to cancel the initial gcode lines and print only the end , and the printed model is not straight.

Edited 1 time(s). Last edit at 08/02/2017 06:29AM by DapDeveloper.
Re: COREXY layer shift
August 02, 2017 07:21AM
Thinlk about how the corexy mechanism works. What is different about 45/135 degree printing?

.

.

.

OK, I'll tell you. When you're printing infill at 45/135 degrees, only one motor is turning. One motor has to provide all the force to move the entire Y axis, which means the X axis and extruder carriage. In i3 type machines, layer shifting almost always occurs in the Y axis because of the moving mass. This is exactly the same problem, and the cure is exactly the same. Turn down the acceleration until it stops skipping. You may need to tweak the jerk/junction deviation, too.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: COREXY layer shift
August 02, 2017 09:32AM
I just finished the printing with accelerations/2 , nothing change...
Re: COREXY layer shift
August 04, 2017 02:19AM
With only 0.1mm layerheight, the nozzle will hit any small overextrusion.
Can you hear the nozzle scratch? Did you try to reduce extrusion ratio?
Printing the top part as solid would probably help too. ( define solid infill threshold or increase perimeters )

Q: Is 0.1mm layer height optimized for mm/fullstep ? I always use layer heights that are multiples of my mm/fullstep value.

Edited 1 time(s). Last edit at 08/04/2017 02:23AM by o_lampe.
Re: COREXY layer shift
August 04, 2017 09:49AM
Silly me, I assumed you had examined the machine carefully and ruled out mechanical problems like loose belts, loose pulleys, incorrectly laid out belts (unparallel to the guide rails, etc.).
Dragging the hot nozzle over overextruded plastic shouldn't cause layer shifting unless you're operating everything at the absolute edge of its limits. That's never a good place to operate anything.

Quote
DapDeveloper
I just finished the printing with accelerations/2 , nothing change...

Quote
the_digital_dentist
Turn down the acceleration until it stops skipping.

What are the acceleration settings?

Maybe a few photos of the printer, clearly showing the belt arrangement of the XY stage, would help...

Edited 1 time(s). Last edit at 08/04/2017 09:52AM by the_digital_dentist.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: COREXY layer shift
August 06, 2017 01:00AM
If it's only happening on longer / larger prints, then my guess is that your stepper drivers or motors are overheating. Try putting a fan over the stepper drivers and / or reduce the current slightly.

Check how hot your motors are getting during the longer prints. If they get really hot, then you have the current set too high for the motors.

Edited 1 time(s). Last edit at 08/06/2017 01:09AM by xyze.
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