X Axis losing home position?  

RE: X Axis losing home position?

I have had the same issue on two prints. It seems the printer is loosing his knowledge of the x-axis position and starts printing more to the left. It happend with prints via ocotoprint and from the sd card.

RE: X Axis losing home position?

The printer does not actually "remember" or even know its actual physical print head location. It assumes that it never skips a step during operation. The homing operation at start of print is to put the print head in a repeatable start location.

If anything causes the printer to fail a step, the printing location shifts. Fixing the problem means tracking down the mechanical problem(s) and correcting them. The things to check are numerous, but you have to methodically find and fix them before the printer will work properly.

Things that are too loose

Motor drive pulleys with incorrectly positioned set screws. One set screw MUST be tightened perpendicular to the motor shaft flat before the other set screw. 

Belt tension so fantastically low that the belt skips teeth. This practically never happens. Natural tendency is to set tensions too high.

Things that are too tight

Bearing clamps set too tight cause bearing binding.

X-carriage backs too tight can deflect bearing alignment

Things that are misaligned or badly positioned.

Rods that are not fully seated in their holders cause binding.

Motor pulleys put too far in or too far out on motor shafts. They should be positioned so belt runs pretty much centered in pulley.

Extruder cable wrap putting excess tension on x-carriage at either end of travel. You may need to loosen and adjust cable bundle twist to alleviate excess tension. This is a LOT easier to check with the belt REMOVED.

Belt tension too high. Only about 6 lbs force should be your tension. Going higher overloads motor bearings.

Things that are poorly lubricated

Bearings need to have been cleaned and lubricated prior to assembly. Failure to do so accelerates bearing wear and results in eventual bearing seizure.

Mechanical Crashes

Check that all cables and carriables don't snag or run into things.

Sometimes prints will cause crashes as bad print points rise. Check that you are not having crashes.

All the above things to check are trival for those who build from a kit, but may initially seem overwhelming to those who didn't build their machines. Just chill and systematically get all those mechanicals corrected. Once done properly, you can expect your machine to run reliably for quite a long time.

RE: X Axis losing home position?

@guy-k2

The issue is not about failing a step (at least in my case) the issue is that if a print goes wrong and you cancel; the next time you try to print it will fail if the print head is not physically moved to the left of the printer (which can only be done by turning the printer off, unplugging, and manually moving it.

This is not the case for the z or y axis and wasnt the case for the printer until about march or so (i forget which update).

If a video is needed to make this more clear it is very easy to replicate.

RE: X Axis losing home position?

I am having the same issue.  After 4 hours of printing a wide (240 mm) it crashed off the right side.  After many recalibration attempts, I finally got it calibrated...when attempting to reprint, it started the first layer too far right and ran off the right edge and crashed.

RE: X Axis losing home position?

@richardherold

Except it still is.  Each time you start a new print assuming you have the homing gcode in your start code then the printer will try and reset home by moving to the front left corner.  The method the Prusa uses is to measure the motor currents, when it goes above a certain value it assumes its has hit the limit of travel.  This is why there are no physical end stop switches on a prusa.  However if there is a mechanical issue such as increased friction on an axis then the printer assumes it has reached home at sets that location as zero for that axis.

To me it sounds highly likely that your X axis needs tearing down and lubricating properly as it is getting friction on left travels.

The thresholds and process used for calibrations and printing are also different so just because a printer passes calibration does not mean you don't have a mechanical issue with friction.

RE: X Axis losing home position?

My "X-Axis Point Offset" (Support/XYZ Cal. Details) has a value of -5.20mm

Could this be the cause of my problem?

If so, how do I adjust?

RE: X Axis losing home position?

You are most likely trying to find a software solution to a hardware problem. It's a rabbit hole of frustration. Get the mechanicals confirmed.

DISCONNECT your x-belt from the x-carriage. Emphasis on DISCONNECT. I don't mean approximate the effects of disconnection by turning of the printer. I mean DISCONNECT the belt completely. That will fully isolate the x-carriage mechanicals so you can actually check its freedom of motion.

The x-carriage must be able to move the entire distance left/right without any catches at all. You may feel catches more readily by pushing the carriage with the far end of a pencil rather than directly with your fingers. If you find any notching or catches, check your bearings, their lubrication, and/or bearing cover bolt pressure.

There will be some light, springy resistance from the extruder cable bundle. It must not unduly prevent the carriage from easily reaching both ends of travel. If the extruder cable bundle is impeding the x-carriage motion too much, try loosening the cable clamp, reducing the tightness of the wrap and reclamping with x-carriage positioned about 70% of way towards right.

Only when you have the disconnected x-carriage moving freely is the printer going to give reliable operation. 

Testing carriage motion with the belt connected hides underlying mechanical issues. Test and perfect the axis freedom without the belt. Once you get the basic mechanicals corrected, reconnect the belt and proceed.

RE: X Axis losing home position?

@neophyl

Thank you very much I will try this!