Temperature Drop mid print

[longshot]

Need a little bit of help. So the printer has been going steady for a few weeks now. I've been printing out items for an upcoming halloween party and just now ran into my first snafu. I was on the last bit of printing when i noticed the startup temp was not coming up to temperature as quick and would sit at 198.4 degrees with a target of 200. As a result the unit would just hang, unable to reach the target temp to print.

Keep in mind I have been successfull in printing through about 3 spools of plastic with little error other than just user error. Nevertheless, I killed the print job, restarted repetier and my computer and viola, temp was reached and print could start.

About 2 hours in i went to check and noticed that the print head was printing about 0.5 in above the last layer with no plastic being pushed out. Naturally i check the spool. Sometimes they have a way of winding up and tangling themselves up. No issues there. I looked at my temp it shows 173. At that temp PLA wouldn't melt so i'm thinking great, now i have a plug (my first one). I tried to coax the machine slowly by retracting and extruding to no avail. A plug was evident. I had no choice but to shut the machine down and dismantle the entire hot end.

I did find a plug.

So my question to everyone, what should my next course of action be?

Is it a power supply issue? Perhaps in the long hours printing i pushed it too far? Does it need to be replaced?
Do i change the thermistor? Keep in mind this is only the 2nd time i've taken this hotend apart, so there shouldn't be any crazy fatiguing going on in the wires.
Should i change the entire hot end??
Could it be a resistor issue? I don't understand what would have changed from before to now. There were no major adjustments made.

Please help.

[lordbinky]

If you are using an EZstruder (I don't know about other ones) careful you don't chew through the filament trying to retract and extruding. Pressing in the top of the bowden tube connectors (and maybe a little wiggling on the tube) should let you pull the bowden tube out with trivial damage. This give you direct access to the filament at the hotend where you can work the filament by hand after bringing it up to temperature, much easier than doing it through the bowden tube.

Give your hotend a good look over. Check connections, check the wires and the tube/sleeving on the resistor wires. You are correct in questioning the thermistor and that seems a likely issue, it isn't uncommon for the thermistor to get displaced after many hours of printing or just handling the hotend in general, especially without strain support. If you haven't zip-tie it down with slack in the length to the thermistor so it never gets pulled on during a print. Also if it says your temp is low enough to not melt the plastic, but you have ooze or can extrude anyways, it is a sign the thermistor is an easy tell that the thermistor isn't making proper contact in the hotend.

If you don't find anything, it could also just be time to run your hotend autotune again.

edit: completed a sentence.

[longshot]

Quick question, how much run time can one get using the same rostock max hot end before replacement. I ask this because most professional machines have xxx amount of hours per tip before they have to be removed and replaced.

Thanks this helps me narrow down what parts i possibly need to replace. Yeah i got the old school extruder. . . its fine for now but definitely looking at an upgrade for that guy. I'll get a new thermistor and just replace it, better safe than sorry. I rather not have another jam or worse have a hot end melt down on me.

I'll clean up the connections apply some more of the hightemp RTV and autotune. Not sure if I'll have it up and running to print the last part of the costume but oh well.

[Eaglezsoar]

Quick question, how much run time can one get using the same rostock max hot end before replacement. I ask this because most professional machines have xxx amount of hours per tip before they have to be removed and replaced.

Thanks this helps me narrow down what parts i possibly need to replace. Yeah i got the old school extruder. . . its fine for now but definitely looking at an upgrade for that guy. I'll get a new thermistor and just replace it, better safe than sorry. I rather not have another jam or worse have a hot end melt down on me.

I'll clean up the connections apply some more of the hightemp RTV and autotune. Not sure if I'll have it up and running to print the last part of the costume but oh well.

I don't believe you can place time for replacement restrictions on the hot-end. There are no moving parts and nothing that really wears unless you exceed design temperatures.
I do believe that it would be wise to perform maintenance on the hot-end, perhaps on predetermined schedule. I would include dismantling the hot-end and checking/replacing the
PTFE tubes and a thorough inspection of the Peek and the nozzle. The most important element is not to exceed design temperatures and to inspect for thermistor and wire problems
before they have a chance to cause problems.

[lordbinky]

I agree with Eagle.

Other Hotends like the E3D have you use kapton tape to secure the thermistor, if you do it properly you can get away with that method as well or do that in addition to the RTV if you don't want to wait for the RTV to fully cure before you print.

Either way,just make sure you keep a close eye on the printer until you are very sure the thermistor is set correctly and secure.