[Solved] MK4 filament runout failure - what did I do wrong?  

RE: MK4 filament runout failure - what did I do wrong?

Good news, it wasn't anything I did! Something in the filament sensor was borked, had to take the front cover off and use compressed air to blow out the area. That seemed to do the trick.

RE: MK4 filament runout failure - what did I do wrong?

Seem to be hearing many reports of this one issue. Wonder if its a widespread problem, or whether these is something that can be done as general maintenance?

RE: MK4 filament runout failure - what did I do wrong?

I wonder if it has to do with running out of filament. That seemed to be the general theme when I was searching for solutions.

RE:

Was your printer pre-assembled or a kit?

I wonder if it’s the ball on the end of the spring by the filament sensor. When filament is inserted the ball is pushed back and the magnet triggers the sensor, informing the printer that filament is inserted. I have a feeling that this ball may be getting stuck, hence the magnet is stuck in the pushed back state, and the sensor remains ‘active’ as the printer thinks the filament hasn’t been removed successfully. 

Some have mentioned that moving a magnet close to the area has got it working for them. 

Others, like yourself, use compressed air to ‘clean the area’. You can also shoot compressed air into the little hole on top of the extruder motor itself - this hole is there for that purpose. 

Either way, I wonder if both the above ‘solutions’ are simply pulling the filament ball back into position, hence the sensor resets and new filament can be inserted, triggering the entire mechanism again……

If you can be bothered, it may be an idea to disassemble the extruder somewhat and check the filament sensor ball/magnet/spring to ensure they are correctly in position. The small plastic holder they are in should be fully inserted and flush with the metal heatsink.

To see what I mean watch from the 1:00 mark in the below video:

Nextruder Assembly

I could be completely wrong, but this is the only reasonable explanation I can think of thus far!

RE: MK4 filament runout failure - what did I do wrong?

Pre-assembled MK4.

I did try blowing air into the little hole at the top, that didn't help. I also tried inserting filament, wiggling, inserting & removing quickly, etc. Wasn't getting far, then came across a post from someone who removed the front cover and blew it all out.

RE: MK4 filament runout failure - what did I do wrong?

I had a similar issue yesterday. I knew there wasn't enough filament for the print and relied on the sensor.

In my case, the sensor failed to work and it printed on air for a while. Had to open the extruder and use pliers to pull out the old filament as it was just a hair above the top of the metal nozzle tube.

After that, it also would not recognize that the filament was. Blew into the area a few times and it recognized there was no filament but wouldn't "see" the filament I was inserting until I blew into it again and sort of poked the filament in and out a few times.

I haven't tested runout since, but I'm sure I will in the next day or so.

RE: MK4 filament runout failure - what did I do wrong?

Hi Jason, 
the filament runout housing has some relatively narrow passages within it, and when the end of a roll passes into the sensor, there is a chance that curvature in the filament may cause the end of the filament to deflect to one side or the other, and act like the barb on a fish hook, latching within the filament sensor housing. 

Often filament rolls have a bent part where the filament is inserted into the spool,  during winding, 

If you can see this as the roll approaches empty, and cut it off, before the filament ends, you can often prevent the filament snagging inside the filament sensor. 

Prusament used to have this issue, however I believe more recent rolls of Prusament have a different setup which precludes this issue. 

In the UK, a company called 3DQF, has cardboard spools with a special access port, where the end of the filament is exposed to the outside of the spool, so that you can cut the end off, before the spool runs out. 

otherwise, if you can see the end of the filament as the spool comes to an end, give yourself a little insurance and cut the filament early. 

it is sometimes better to cut the filament before the end so that you can monitor the change. 

On this print, every filament change was manually executed, I cut the old filament, watched the end go inside the extruder, then inserted the end of the new filament into the extruder and gently pressed it in, until the extruder hobbed gear caught the end of the new filament and fed it through. in the colour changes here you can  just see the colour transition as the new and old filament morphed from one colour to the next. 
In this print the filament sensor did not trigger at all. 
obviously if you are not changing colour, there will be no colour morph. 

regards Joan

RE:

He's not alone! I got about 87% complete on a print that was running for over 9 hrs. to come back and see that the printer had not paused when the filament ran out and the printer kept going with no filament. This is very frustrating when a large print like this is completely ruined. 

Is there a fix for this issue?

David

RE: MK4 filament runout failure - what did I do wrong?

Woke up to this issue this AM. Over 10 hours into printing the internal MMU3 buffer mod from BlueX and the hotend continuing oblivious to the fact it was 1cm above the print. Had to swap nozzles and restart. Now left with a blocked nozzle. Guess I'll have to try and warm up and then purge. The tiny piece of PETG sticking out the top of the nozzle wasn't enough to pull it out and just snapped so hopefully it will purge OK.

Kit built MK4S