ABS Stops flowing / Hot end Jamming / Suicidal urges

[Octavio]

Hello Everybody,

I finished assembling my Rostock MAX just recently and I have not been able to get a good piece out of it.
I'm testing it with the hallow cube and after millions of different problems (blown thermistor, ABS not sticking to the heated bed, heated bed not reaching the 90˚ temp) now I'm stuck with pieces that start nicely and end up bad.
It seems the flow of the melted ABS starts failing in the middle of the piece. To the point where it stops flowing at all; even with the manual extrusion.
I've helped the machine by pushing the filament while it is being pulled with the motor, and this has worked and started the flow again, but it's so inconsistent that I just can't print.

Here is a photo of two bad pieces (I have lots more finished in the same fashion, but earlier in the process...):
https://www.dropbox.com/s/iyle8lzsnm89b ... owCube.jpg

Does anybody know what is the problem or even better, the solution?
Some Facts:
Software: Repetier Mac / Slic3r (the latest)
Settings: Pretty much what the Rostock manual tells you to do with a few variables in speed and temp.
; layer_height = 0.2
; perimeters = 3
; top_solid_layers = 3
; bottom_solid_layers = 3
; fill_density = 0.4
; perimeter_speed = 10
; infill_speed = 30
; travel_speed = 200
; nozzle_diameter = 0.5
; filament_diameter = 1.75
; extrusion_multiplier = 1
; perimeters extrusion width = 0.85mm
; infill extrusion width = 1.02mm
; solid infill extrusion width = 0.85mm
; top infill extrusion width = 0.85mm
; first layer extrusion width = 0.60mm


Many thanks in advance!

Octavio

[Flateric]

Photo link is dead......Really hard to help with nothing to look at sorry.

[Octavio]

Hello,

I'm very sorry.
Here is the link:

https://www.dropbox.com/s/iyle8lzsnm89b ... owCube.jpg

When not even the old copy and paste works...

Octavio

[MDMD]

Check to make sure you aren't getting plastic flakes on the extruder bolt. If the extruder gets gunked up the plastic will slip and cause problems like what you are having.

[626Pilot]

; perimeters extrusion width = 0.85mm
; infill extrusion width = 1.02mm
; solid infill extrusion width = 0.85mm
; top infill extrusion width = 0.85mm
; first layer extrusion width = 0.60mm

Extrusion width should be the same as the nozzle diameter or a little more. Usually people add 0.05 to the nozzle diameter. Change all of these to 0.55 and your prints should get better. Avoid going under the nozzle diameter (usually doesn't work at all) and don't add more than a few percent. Your infill extrusion width is 1.02mm, twice the diameter of your nozzle, and that's guaranteed to make a mess. Infill may not show from the outside, but it needs to be laid down clean or it's likely to mess things up sooner or later.

It also looks like you may not be pushing enough filament. Best thing to do is get a micrometer (definitely NOT calipers - get one of these), measure filament width in at least 5 places a few centimeters apart (discarding any outliers), then put the average into your slicer software for the filament diameter.

With those two changes you'll probably see a noticeable improvement in your prints.

[lordbinky]

Did I miss where you said your temperature? Also keep an eye on your extruder temp during the print, I had a 24V 40 Watt heater cartridge that was sold as a 12V 40W and after the first couple of layers it couldn't keep the temperature up and would cause funky prints.

[Octavio]

Hello!

The temp is pretty stable, fluctuating +-2.5˚ form the 240˚.
I've changed the width settings to .55, but my problem is way before all that.
It doesn't extrude!
Sometimes at all, sometimes very little so I don't get 100 mm when I extrude 100 mm. Between 15 and 40...
If I push up the ABS while extruding, I feel lots of resistance and I manage to make more material come throught the nozzle, but without that help I can barely see anything coming out...

Thanks again

Octavio

[lordbinky]

Well... If you haven't calibrated your thermistor (search the forums it's come up a few times) then 240° may have damaged your hotend. The thermistor can very easily be off by 10°C, and the peek section of the stock hotend's melting point is 250°C. If you're not using an all metal hotend such as the E3D but are using something like the j-head you may have deformed your tube which isn't so bad but still would need reworking or replacement. So, here's what I'd suggest.

Check your bolt in the extruder make sure it's clean, you can up the current in the extruder motor in your firmware, you can knock it up to 195 and see if that helps, you'll want to reduce it back down to a lower setting so it doesn't get so hot that it stops for a moment during a print while it cools off but it will help identify or eliminate a problem. Check your bowden tubes and make sure they are being held firmly and and pushed in all the way and make sure there aren't any weird bends or kinks in the tube that would add resistance. If that fails take the hotend apart (when it's cool...) and check out all the pieces in it for any signs of damage or odd shapes/sizes etc.

[designfactore]

Hey Octavio,

Get it sorted out yet?

I had an issue with similar "symptoms." My print would start out fine, then somewhere along the way, and not always at the same point, it seemed as if the plastic wouldn't flow out fast enough. Like you, I found pushing it with my hand during the process helped at that moment, it would print fine for a few layers, but then the same thing would happen again.

Well, I sorted my issue out. In my case, my troubles started when I added a second extruder (EZStruder). The steps per MM were just a little too high, and also, my retract speed settings were too fast for the EZStruder. The Steve's Extruder is capable of much higher speed apparently, and I thought the EZ struder could keep up.

The result of the apparently aggressive settings (steps per MM, retract speed) was that the EZstruder, which only grabs the filament from one side, can't deal with pushing as fast as the Steve's Extruder. Because it grabs from only one side, all that pressure is just one that one side of the filament. The EZStruder was thus stripping a notch out of the filament and losing its grip, so it couldn't push after a certain point-- it didn't have enough to "grab onto." I realized this when I had a print start failing due to plastic flow stopping, and when I manually pushed the filament through and looked in the bowden tube, I could see the gouge. BINGO!

My suggestion to you is:
--check your steps per MM setting in your firmware
--turn retraction off
--and set your speed multiplier in Repetier down low, like 25%, and try your print again.

On a tangent note, that's the reason I prefer the Steve's extruder, because it grabs from two sides. Much fewer issues, the time you save down the road is worth dealing with screws to change filament.

[Octavio]

Hello again,

I've just disassembled the hot end and discovered the following:
The inner teflon liner (thinner one) has a change in diameter in the last 4-5 mm so when the ABS goes in, it moves without difficulty until it gets to this smaller diameter section where it get's stuck.
Even with my hands it is difficult to push it so it goes through.
Is this normal?
How did this happen?
Can you advice?

Under the circumstances (not being able to extrude material, period), all other settings seem unimportant.

Thanks again,

Octavio

[geneb]

A side effect of over-heating the hot end is the inner 2mm PTFE liner can shrink enough to prevent filament from passing through it. You'll need to replace the inner liner.

g.

[626Pilot]

Put the liners back in the hot end and heat it up to temperature, then remove them with needle nose pliers and see if you can separate them. Try pushing or pulling, and twisting, at the same time, and be careful not to crush or deform the tubing. You may be able to remove a thin film of burnt plastic that might be in there. There will probably be some burnt plastic on the outside as well. If either liner is messed up, replace it.

[Eaglezsoar]

Before changing the liners, I would stick a thermocouple in there down to the nozzle and measure what the thermocouple says the temperature is.
You need to know the exact temperature so that this doesn't happen again.