Extruder changes its position during print  

RE: Extruder changes its position during print

Definitely not normal.  It should have printed in the middle (btw thats called a skirt, not a brim), and when finished it moves the bed forward making the part easier to get to.  The 'rumbling' was the y axis motor trying to move the bed when it was already at the physical limit.

Positional errors like that are 'usually' down to sticky bearings that have not been lubricated.    With everything powered off the bed and X axis should move smoothly and freely back and forth with no troubles. 

The thing that's bugging me about that though is with a sticky bearing I would expect the part to only be offset by 1 size of the part, so not that far back.  

What version firmware are you running ?

I take it this is with the pre-sliced models from the sd card ?  It might be worth slicing a a simple model (even the same model as it can be downloaded) and trying again.  Also does it do this everytime with the gcode from the sd card ?

RE: Extruder changes its position during print

@neophyl

Thanks for your feedback.

• Yes it is correct the HeatingBed was moved forward after the print (as shown in the picture)
• My MK3S is a completely new built machine. As stated in the handbook - the bearings are pre-lubricated, so there is no need to do so.
• When completely turned of the HeatingBed does need some "minor" force to slide back an fourth, but that I think is due to the magnetic spool of the Y-Axis motor. Have said the HeatingBed is not self sliding when bringing the printer in a vertical position. Funnywise the X-Axis is sliding smoother.
• Yes the big offset is crazy, I just tested an other model from the PRUSA SD Card (the little Boat). The same but problem but at a later stage.
• I'm running the latest Firmware version
• Yes I was using the pre-sliced models from the original sd card.

What I also realize is that when I run the "First Layer Kalibration" everything works fine. After the calibration the HeatingBed is moved forward like you said. But when I start the print now direct from the sd card the extruder is not moving to the start position. Instead it starts the leveling procedure at Point Nr. 7 (see picture) followed by 8 then 9. When it comes to the next Row of leveling points the Y-Axis is rumbling, the Extruder changes its X-position to the levt and runs the next 3 point, but again at the same position (7,8,9). The same repeats one more for the last 3 leveling points. --> This is just because initially the original starting point is not used.

RE: Extruder changes its position during print

WTF. I can calibrate the printer as much as I want to but there realy seems to be a big issue here. The Assistent is telling me „all fine - Happy Printing“. And so I Terry - but it‘s always the same. The Printer starts but it changes its home position (for about half the lenght  of the Y-Axis) and continuous printing (in possible die to the final lenght of the HeatBed).

When I stop the Print (Reset Button), I realize the Home Position is completely lost. The HeatBed can only be moved minimal.

The Belt is not tigthened to hard, the bearings  are perfectly running smooth, the firmware is at its latest release (original installed by PRUSA), calibration was done extremely serious.

Any Idea

RE: Extruder changes its position during print

This is 100% caused by the dirty sheet...the forum has taught me that much.

After a good cleaning, I would do an actual, full factory reset....then I would reflash the firmware.  After 7 more sheet cleanings, power on and try the calibration again.

maybe skip the last cleanings......but the firmware flash will give you a solid starting point to troubleshoot if its still messed up

RE: Extruder changes its position during print

Just my thoughts......but Ive seen crash detection restart in some bizarre positions.  Have you checked to see if there are crash errors or have you seen it trigger?

I would also suspect the bearings - especially if you did not clean/repack them

RE: Extruder changes its position during print

@nilok

Hey nilok, thanks for your feedback. I always clean the sheet as statet in the manual after each print wit Isopropanol.

Yes there are crash detections butabsolutely no information about what to do in such a case. I will check if a firmware reset would help.

RE: Extruder changes its position during print

Firstly if you really want to see how smooth it is remove the belt from the Y axis pulley and tilt the machine front to back.  it should slide easily under its own weight with just a moderate tilt.

Secondly its VERY easy to over tighten the u bolts on the carriage, its possibly one of the worst design aspects of the mk3.  Going too tight can potentially damage the bearings too.

Thirdly the manual may say that the bearings are pre lubricated but they are not.  They are packed with grease yes, but its the type designed to protect during shipping and storage.  Not cleaning them out and repacking with a proper bearing grease will work for a while in most cases but it leads to premature wear and the need to perform maintenance much much sooner.  

If your printer is not homing to the front left corner you definitely have issues.  The fact its calibrating on 7,8,9 each time means its finding 9 points so it thinks its ok.  Without inspecting it can be difficult to troubleshoot these things but you have to double and triple check the free movement.  It looks like your issues are limited to the bed/y axis so you have some luck there as thats much easier to access and issues with X.

RE: Extruder changes its position during print

@neophyl

Hey Neophyl, thanks for your support, yes, you figured it out - the Y-Axis was the problem but not because of the bearings or the thighness of the belt. I found the solution here in an other post --> Flat First: Drive gears must be tightened flat-first. So I did the following:

1)   I loosened both screws of the Y-Axis pulley completely free and moved the bed back and forth (must move smoothly).
2)   Then I aligned the flat set screw dead center with the flat on the motor shaft and slowly tightened the screw until it fully contacts the flat surface.
3)   Then I tightend the jam set screw, and torque it.

4) Checking the movement of the HeatBed - should still move smoothly

5) Restarted the calibration and did a first Testprint 😉 Yeaii it workes

Thanks for your support, this was important for me.

Keep on Printing 😉

RE: Extruder changes its position during print

Pully is the third most common issue 🙂  First is bed cleaning as Nilok jokes about, second is bearing movement.  Just glad you got it sorted.  Your pully must have been almost completely loose then.  If you see offsets appear then that's usually an indication that they have worked loose. 

One thing I like to do when they are correctly positioned is to take a thin sharpie maarker or similar and draw a line on the pully and shaft (on both x and y).  That way its easy to tell if they are not aligned any more.

RE: Extruder changes its position during print

Almost perfect.