The printing shifts suddenly and randomly in the middle of a layer

After many days since I received my P802N Prusa I3 3D printer i've able to assemble it and solve most of the usual problems except one.

When printing, for instance, the 40mm_box_pillar the head shifts suddenly and continues to print some milimeters away. If left alone it does that until trying to go out of the base.

I cann't find no reason for that because it doesn't happen on the same place. One time it did that on the first layer other times on the 3rd. The best time happened in the middle of the 9th layer.

It happens printing directly from the SD card or printing from the PC with of the Repetier-Server. I have to cut the power or stop the print job to prevent possible damages.

The printer data is:

FWVer: V4.9

Model: P802NA

Repetier: 0.92.9

Zonestar 3D Printer

I haven't change any settings.

The acceleration is set at 800,800,100 fo X,Y,Z.

Autolevel is on.

The belts are tight.

The base is levelled and covered with the paper tape supplied.

I'm using PLA 1.75mm filament.

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Hi Pedro,

I suspect you don't have a printer created by Josef Prusa, but a clone using our design. Therefore it is very hard to provide support. Please ask for a contact on the manufacturer in the shop, where you purchased the printer.

Layer shift are very often caused by loose belts or loose pulleys on the motors.

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Thank you for your answer.

I had that problem first but then I tightenned the belts and now, while it is working, the lines are straight in both X and Y directions.

The problem is that suddenly the printer forgets a move and continues to print shifted from the original position. The belt doesn't jump and there are no strange noises.

I've already complained to Gearbest but got no answer yet.


Might be the memory buffer gets full, so it has to drop something out :/


I thought of that also.

When connected to the PC I configured the connection with buffer of 127 bytes, then 63 and then with 31, but I could see no changes.

When working directly from the SD card I think there's no way to control the buffer size.


I've reset the tension on both X and Y belts, releveled the bed, and the first layers begin quite ok. But after a few layers (6..9) the sifting on Y reappears. I noticed that the noozle begins to drag on top the printed layers, even when printing. Is it possible that this is a Z problem? Can this drag induce the shifting on Y motor?


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Pedro will be eternally grateful.
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