PLA Suddenly Jamming Mid-Print

[curious aardvark]

have you tried using cura ?

[Ryuluce]

have you tried using cura ?

I had tried using Cura in the past, but I couldn't remember too much about it so I tried taking another look at it.
Unfortunately, it looks like Cura is lacking in settings compared to Slic3r. Honestly, I want to have as much control over the slicing as possible, and Cura isn't delivering.

[Ryuluce]

Okay, so through the use of a lot of tweaks of the settings (the process of which was pretty much trial and error; thus I can't really give much depth where there is none), I have found that my current issue that prevents printing is one of two things:
A) I'm printing too cold and that grinds down the filament eventually. Easy enough to avoid.
B) The filament is buckling in the extruder.

Problem B is where I am stuck. I can't tell if I'm printing too much material too quickly and that's smashing the filament, if I'm printing too slow and the filament is heating up in the extruder, if I'm printing too hot in general, or if it's because of some other cause.

Below are two pictures of removed filament, you can clearly see where the filament has kinked and is preventing further extrusion.


If you know what causes this, I'd greatly appreciate tips on how to prevent this.

[uncle_bob]

Hi

Unless you have a really rotten hot end, there is no such thing as feeding to slowly. The extruder and hot end should be able to sit of hours with nothing moving through the system. If you have a really rotten hot end .... it's time to replace it. Simple check: The top of the hot end (where the filament feeds in) should be no more than warm to the touch when in operation. If you can't keep a finger on the top end of it for the count of five, it is to hot.

The simple check is still to tell the extruder to feed filament at the max speed setting. If that feeds fine for foot after foot of filament, the problem lies somewhere else. If it jams, swap out the filament and see if a different brand does the same thing. If two or three brands all do the same thing, your hot end thermistor may giving you bum data or your temperatures are simply set to low.

Bob

[Ryuluce]

Hi

Unless you have a really rotten hot end, there is no such thing as feeding to slowly. The extruder and hot end should be able to sit of hours with nothing moving through the system. If you have a really rotten hot end .... it's time to replace it. Simple check: The top of the hot end (where the filament feeds in) should be no more than warm to the touch when in operation. If you can't keep a finger on the top end of it for the count of five, it is to hot.

The simple check is still to tell the extruder to feed filament at the max speed setting. If that feeds fine for foot after foot of filament, the problem lies somewhere else. If it jams, swap out the filament and see if a different brand does the same thing. If two or three brands all do the same thing, your hot end thermistor may giving you bum data or your temperatures are simply set to low.

Bob

By "top of the hot end" are you referring to the top of the aluminum cooling block, or the top of the entire extruder block?
If it's the former, then there's a problem with my printer's insulation from the hot end to the cooling block. The cooling block gets real hot while printing, so much so that I can hardly touch it for more than a second or two. I kept lowering my print temperature until I reached a point where the prints were still jamming and the amount that did print was horribly de-laminated. I can't print any colder.
I'm worried that the heat is traveling up into the aluminum cooling block and softening the PLA thus allowing it to warp in the extruder.

[Alibert]

In a makerbot-type printer (such as the Qidi Tech you have) the cooling block (the large alu bar which is used to fix the extruder with) will get hotter than, for example a E3D type cooling block. This is normal and a by-product of the design. However, you should be able to touch it without problems.

There are two things that determine the temperature of this block: 1) the amount of heat put into it (from the hotend) and 2) the amount of heat being taken out of it (via the cooling fins and fan).

As to 1): Do you still have the glass-fiber insulation around the heating block? If not, buy some from aliexpress and re-do it.

As to 2): Is the fan running? Is the cooling fin part with the flat side to the cooling block and the fins to the fan? You can improve the heat transfer by putting some thermal paste (as for CPU's in PC's) between the fins and the block (makes it a bit messy when dismantling though).

Finally, the makerbot design was intended to have ptfe lined throats (the part between the cooling block and the hotend) as the cooling block can not make a sharp temperature transition in the throat. If you want to print PLA, you will need this ptfe liner there.

As a beside: I have just installed a micro-swiss all-metal upgrade in one of my Qidi printers to be able to print in the 250-300 C range (polycarbonate and PEI). This one has a two-part throat, an alu outer part (good thermal conductance) and a steel inner/low part (poor thermal conductance) to the heating block. With extra thermal paste between the alu outer part and the cooling block it is claimed to be able to achieve the sharp temperature transition needed. Just tested it at 265 C (PC-MAX polycarbonate) and it worked just fine, no jamming. Will be doing PEI later this week when the sampel comes in (at 280 C).

One last final thought:
I have had a heck of a time in repairing the printer of the local primary school. It would also give all kinds of grief as to jamming, extruder grinding and patchy extrusion. It turned out that the thermistor leads would make contact and short at random times by vibration/head movement (the leads were jammend under a fixing screw keeping the fan in place). This would make the mainboard 'think' that the temperature was suddenly 300 C and it would stop heating. As the heating block cooled down through lack of heating the plastic would solidify and jam. I found that out by using a monitor function to monitor the temperature, heat the hot end to 150 C, and then wiggle the leads of the thermistor. When I did that I saw the monitored temperature jumping up and down. Took me a long time to find that one.

[uncle_bob]

The point that the filament enters the hot end should be cold enough to touch when things are operating. This is the top of the cooler in most designs not the top of the heater block.

[Alibert]

I wanted to give a pic, but I can't upload any ?

[uncle_bob]

If you take the hot end off the extruder, the hot block is at the bottom. Between the hot block and the mount boss is a cooler. Ther top of the cooler should not be hot. Years ago hot ends were designed with poor coolers. Printed extruders melted and the designs improved. Modern hot ends are at room temp at the top of the cooler.

[Ryuluce]

Okay, I know I haven't posted in a while. That's because I have been having intermittent jamming issues and I'm unsure why.


But, here's a new theory: The extrusion stepper motors are getting too hot.


I made a quick test where I left the nozzles heated for a while, and the aluminum cooling block stayed at a reasonable temperature.


Then, when I tried printing something the cooling block was very hot a while into the print and the stepper motors were even hotter on the backs.


I read here ( https://groups.google.com/forum/#!to...ot/gN_W4GieQwk ) that it's possible the stepper motors are running on too high a current. Is that possibly my issue? (As a reminder, the firmware I'm running is Sailfish ver 7.1)