X Axis Crashing
I purchased my Prusa i3 MK3S back in April and finally finished getting it assembled (I took my time on it to make sure I did it right). For the past couple of weeks, I've been attempting test prints from the SD card that came with the printer and troubleshooting this issue.
For a majority of prints, the printer will get started just fine but at a random point in the print, it will lose track of where the X Axis is located, push the extruder all the way to the right, continue pushing it (causing a loud grinding sound), and crash. The print is then unrecoverable.
Upon investigating, I found that the X Axis would have it's 0.0 coordinates set in the middle of the printer instead of the far left after one of these crashes. To resolve this, I have to unplug the printer and manually push the extruder all the way to the left for the X Axis to be realigned again.
This happens on 100% of prints that take more than 1 hour (such as the Triceratops Skull). It happens about 30% of the time on smaller prints (such as the Marvin). I have not attempted any prints that were not included with the printer's SD card.
So far, my troubleshooting has taken me down two paths: 1) The X Axis belt tension and 2) Wiring. The wiring check was very simple - I simply traced all the cables and re-seated every connection to the logic board. That did not improve performance at all.
The belt tension is where I find some weird results. When I check the Belt Status, it shows the X Axis around 130 and the Y Axis around 270. When reading about this, I found that you want these to be between 230 and 280, indicating that the X Axis is too tight and the Y Axis is good to go. So I reworked the X Axis and intentionally set it to be far too loose, in order to test the sensitivity of that measurement so I knew how much I needed to tweak it. To my surprise, I had the belt so loose that the motor struggled to grip it (and I could easily pinch the top and bottom together without any resistance), and the Belt Status measured that at 193. This led me to believe that I could not trust this measurement and something else was wrong. I tested a print just to be sure I was correct on it being too loose, and sure enough -- I had X Axis layer shifting all over the place and it crashed.
I tightened the belt up to a point that I thought was good, and checked the Belt Status again -- 170 for the X Axis. I did a test print and it came out great! It still crashed, but there was no layer shifting, the texture of the print was very clean, and the first layer was pristine (Z Axis calibration is solid!).
Considering the incorrect measurement, I thought the firmware might be the issue, so I updated that. It's now on version 3.7.1-2266 and still seeing the same problem.
So at this point, I'm really not sure what else I can do to correct this. I feel like I have some kind of faulty hardware, but I don't know how to be certain nor do I know how to contact Prusa to get that replaced if needed. Does anyone here have any advice?
Best Answer by --:
Grade 2 Lithium Grease - Superlube 21030 (grade 2 synthetic); Both available most anywhere - HomeDepot, AutoZone, etc. Prusa is dead set in thinking their bearings come pre-lubricated from the factory and make no mention of cleaning and properly lubricating the bearings. Query any bearing manufacturer and they'll tell you bearings ship in a preserving oil or packed with grease.
In a pinch, until you get a chance to add grease, a drop or two of motor oil on the rods both sides of the bearings can help, moving the axes back and forth to work it in. Some folk just use 3 in 1 oil and get by.
It sounds like your X-axis might be binding, belt might be a touch too tight (some have broken the left motor mount trying to reach 240); and there are cases of the extruder housing pinching the X bearings - loosening the rear extruder housing screws a bit has worked for some.
The extruder takes a bit more effort than the sled, but you should be able to move it by hand side to side without any stickiness.
And as a sanity check, I just checked my printer and gravity starts to pull it to a side at 45 degrees. My X bearings are a bit dry and starting to get a sticky spot near the right side, so past time for maintenance.
By the way, those LCD numbers are based on the average current taken from the motor controllers. This feedback is how the printer detects crashes and knows something went wrong. The entire crash detect process is prone to errors, but better than nothing. The idea is when the motor stalls the controllers detect the over-current and give pop up a warning, avoids wasting plastic and time.
RE: X Axis Crashing
Ignore the LCD numbers for belt tension. If you ever got to 240 you'd be bending your printer and motor shafts.
Slide extruder left, bed back, pull up on the lower of the belt pairs with 8 ounces (250g), the belt should deflect 1/4" (6 mm). That is for a 8 lbf tension, which is between the 2 lbf minimum spec, and 11 lbf motor shaft spec.
ps: at 11 lbf, my numbers were pretty close to 300. At 8 lbf, they are still pretty close to 300. aka: meaningless.
Generally, crashes are either sticky bearings (you did grease them before installing, right?) - and nozzle crashes cause by plastic curling up into the nozzle path. Powered off, the bed should slide on its own if you lift the front of the printer; and the extruder should slide to the opposite side you lift on. Mine starts moving around 20 degrees.
RE: X Axis Crashing
Thanks for the reply, @tim-m30! Great to know that the Belt Status numbers are meaningless -- I really didn't feel like I was getting anywhere with that.
To note, I did NOT grease the bearings before installing -- no note of that in the installation manual at all, so I didn't know it was required. I did conduct your test -- removed the filament and powered off the printer. Tilted backward for the Y Axis -- it started to slide back at about 45 degrees (same with forward). The X Axis did not slide on its own at all. I turned it completely on its side and the X Axis stayed right where it was the whole time.
If the bearings for the X Axis are the problem, can you recommend some grease I should buy? And could you tell me how to properly apply said grease? I've never done that sort of thing before, and this is my first printer.
Thank you for the advice!
RE: X Axis Crashing
Grade 2 Lithium Grease - Superlube 21030 (grade 2 synthetic); Both available most anywhere - HomeDepot, AutoZone, etc. Prusa is dead set in thinking their bearings come pre-lubricated from the factory and make no mention of cleaning and properly lubricating the bearings. Query any bearing manufacturer and they'll tell you bearings ship in a preserving oil or packed with grease.
In a pinch, until you get a chance to add grease, a drop or two of motor oil on the rods both sides of the bearings can help, moving the axes back and forth to work it in. Some folk just use 3 in 1 oil and get by.
It sounds like your X-axis might be binding, belt might be a touch too tight (some have broken the left motor mount trying to reach 240); and there are cases of the extruder housing pinching the X bearings - loosening the rear extruder housing screws a bit has worked for some.
The extruder takes a bit more effort than the sled, but you should be able to move it by hand side to side without any stickiness.
And as a sanity check, I just checked my printer and gravity starts to pull it to a side at 45 degrees. My X bearings are a bit dry and starting to get a sticky spot near the right side, so past time for maintenance.
By the way, those LCD numbers are based on the average current taken from the motor controllers. This feedback is how the printer detects crashes and knows something went wrong. The entire crash detect process is prone to errors, but better than nothing. The idea is when the motor stalls the controllers detect the over-current and give pop up a warning, avoids wasting plastic and time.
RE: X Axis Crashing
Reporting back! I got some grease and applied it to both rods for the X Axis and slid the extruder back and forth to get it into the bearings. I probably applied way too much grease, but it was still a challenge to push it back and forth.
I did a test print and it crashed within about 15 minutes; same symptoms as above.
So I opted to try the other suggestion you had -- loosening the screws on the rear extruder housing. I then applied a little more grease and moved the extruder back and forth to apply it, and it felt much more smooth.
I'm not sure we're in the clear yet, but we're about 15 minutes into another test print and it hasn't crashed yet, so that's good! I'll report back with results as I test further. Thanks again for the help so far.
RE: X Axis Crashing
Reporting back to note that this is solved. I've conducted several tests since tim-m30's suggestions. What really did it was loosening the screws on the rear extruder housing. The grease helped a bit too. We're now working smoothly! Thank you!