Possible z height jump on a filament load failure query  

RE: Possible z height jump on a filament load failure query

I've experienced this multiple times now, except it's been going down.

I've been getting a lot of load failures (some are just due to the filament slipping out the back of the MMU during printing, others I believe it's getting stuck in the PTFE tube leading to the hot end, but past the extruder gears so the filament sensor says its loaded fine) and 4 times this week, after successfully completing a filament load with my help it has then buried the nozzle into the purge block when it tried to continue printing.

The only thing I can imagine causing this is a bug in the firmware. I have now made an issue report: issue 4504

RE: Possible z height jump on a filament load failure query

I haven't had a further problem since I first posted (as I have had no load fails to check the recovery).  I have also since upgraded from 3.13.1 (3.0.0) firmware the latest 3.13.2 (3.0.1) . I think my load fails were more due to bad filament (old and brittle) however it was the recovery from the load failure that caused the problem. 

Also my machine config may be a little different to others as when I upgraded from MMU2S to MMU3 I did not change the extruder chimney stack from the Mk3S hardware (I did not upgrade to the Mk3S+ version which looked to me was reverted to the MK3S type in the MMU3 conversion instructions).

Will post again if the problem reoccurs.

cheers

RE: Possible z height jump on a filament load failure query

I have attached an example of what appears to be a layer skip in a MMU3 print.  I wasn't watching the printer at the time so I am hypothesising that there was a loading problem which was automatically recovered by the printer but skipped the layer.  (In the pic the light brown had the load fail, skipped the layer, perhaps tried to print the next light brown layer, changed tool head to the dark brown which printed Ok and continued on.) 

I will reprint just to make sure it is not a gcode issue...

RE: Possible z height jump on a filament load failure query

That usually means you had some sort of tangle in your spool so it couldn't pull filament in to extrude for a partial layer or more. Then at some point the printer literally pulled through the tangle and resumed as normal.

RE: Possible z height jump on a filament load failure query

Thanks but no tangle in this case. MMU3 firmware has automatic re tries to load the filament (different to MMU2) which is what I assume it did for this case. if it doesn't succeed it stops and prompts for manual intervention (which has happened in the previous occurrences of the issue)

RE:

I'm not claiming a feed error. What I'm saying it loaded fine, but at some point afterwards, while printing that layer, filament stopped flowing. In my experience usually a filament tangle (or filament sticking to itself) because nozzle clogs would affect everything afterwards not just a single color on a single layer. But since the filament sensors are on or off rather than detecting flow, the print continued on "without error" resulting in a skipped layer. That layer's filament retracted fine and when it was its turn again to be fed the speed/acceleration was able to pull through the "tangle" and resume as normal.

Its very possible that it was something else. But I've never experienced anything similar which only affects one color (one spool) for just a partial, or more, layer.

The MMU will never just skip a layer esp if there was an error. It will wait for hours and hours requesting manual intervention.