Z crashing to bed after 4-5 layers
Sorry if this is in the wrong place, this is my first time using the forums.
I've had my Prusa MK3 kit for 5-6 years now, it's been good to me and I've gotten hundreds of good prints. Lately, I've been having issues with either the top. Layer being terrible after 99% of a print working or after 4-5 good layers the printer "dives" in Z and crashes into the bed/print. My only warning is that preceding it starts to scrape the layer below as if it moved up only half a step. Then it will catch/crash and all axis go wild. I should note, this is all. In silent mode.
Any ideas on where to start troubleshooting?
RE:
I have a MK2.5 (5-6 years old or so) and hope this will not happen on my machine. So happy to help you analyze (so I can prevent the same on my printer 😉 )
- Z height is driven by the spindles turning more/less to right/left.
So what happening when it "dives"? Are the spindles (so also the stepper motors) turning? And if so, both sides same amount?
If so, then there is something sending commands to the steppers to make so much turns.
If not, and it dives (without turning spindles) then the spindle nut(s) must be worn out, and it just slips over?
If so, then probably not right + left at same time and same amount. So it should go skew also
I can hardly imagine this is the problem, but if not asked, no answer.
- If the dive comes because the steppermotors drive it down.
Question: Does the dive go "Into" the heatbed, so below 0,15 mm?
Because that is the absolute border, the firmware will not go below.
If it goes below, then this weird command to do many steps, is not "passing" the software (if you could say it, that way). You would get and error-message (NB: Maybe you get an error, but did not mention it? )
No error-message? Then I would search in the output circuit between PCB and Z-steppermotors. The cables are paralel so all steps go to both motors at the same time (so the X-axis stay perpendicular).
Check the connectors, + cables to where they split in two cables (for every motor). Maybe a loose contact or almost broken cables gives pulses what are seen as commands.
If there is such an issue, then there is also the question, why it works at one moment and gives a problem at another moment?
The cables to the Z-motors do not move (in normal functiong), so maybe a moving part of the Y-axis is touching/pulling it?
Bad contact, USB
Another thought, is that the G-code is transferred badly to the printer.
Is it when printing of the SD-card? Or when coming from USB?
Same problem with all g-code-files?
Every time the exact same issue at the same place in the print?
If random, a bad SD-card or USB is more likely.
If everytime the same issue with 1 G-code file? -> Bad file
Or with all G-code-files -> Bad software? You did a firmware update lately?
I would start with checking those connectors and cables.
+ change from USB to SD-card or vice-versa to check if there is a issue there.
We will do what we have always done. We will find hope in the impossible.