beady plastic extrusion, and clogged nozzle

Hi guys,

So I am printing, there are 3 problems:
1- my extruded plastic is a bit beady. I'm thinking it might have to do with temperature, basically the beads are timed with the extruder cold end stepper motor. This is an image showing a line of printed plastic. I've tried different heights, it does the same thing until it touches the bed. It doesnt seem to be a height issue.

2- Sometimes, after cooling, my nozzle is clogged. There seems to be solid plastic higher than where I'm able to melt it so the nozzle is clogged. The problem is that on my next print i have to open up the whole thing and cut the plastic so that it can be fed again. This means I need to remove the nozzle and hot end.

3- It looks like my roll of PLA does not unroll very well and so the extruder is pulling on plastic until it can't pull anymore, then it doesn't extrude anymore.

If the extruder motor doesn't run smooth, check if it does without filament. If so, you may need to adjust motor current and/or solve the filament feed resistance to the extruder. You didn't mention type of printer or extruder type so can't be more specific.

Is your cold end cooled with a fan? What type of hot end are you using? Does the gcode retract at the end and by how much?

A spoolholder with a guide may help. I use one with and arm with a hole in it that puts a little resistance on the filament so that the filament doesn't unspool by itself, which is often the cause of tangling. If the spool is poorly wound, try a different brand. I like spools that have a bigger diameter and less wide. The wider ones seem to tangle a lot and are too tightly wound, snapping off when straightend by the bowden tube. Hips is much better in this regard, it bends rather than snapping off.
At one time the printer was pulled nearly off the table because the spool was stuck.

Thanks for the reply,

1- the extruder motor is of the style which uses a spring to apply pressure to squeeze the PLA filament between the motor axle and a free wheel as shown in this photo.

2- The end of my instructions look like this, which retracts the PLA by 2mm. Is 2mm enough?
Also, would this mean that when i interrupt a print midway, I should manually retract the PLA? is there a limit to how much I should retract?
The fan is running DC constantly and blowing on the heat sink part of the extruder as shown in this photo.
G1 X10.713 Y-7.200 E6.14310
G1 X11.999 Y-5.913 E6.26813
G1 X11.179 Y-5.565 E6.32940
G1 X10.711 Y-6.033 E6.37483
G1 E4.37483 F2400.00000
G92 E0
M107
M104 S0 ; turn off temperature
G28 X0 ; home X axis
M84 ; disable motors

3- good to know it's not just me who has this problem. The guide sounds like a great idea. Perhaps would be a good project to 3D print!

1. I mean the stepper motor, what you describe is the extruder/extruder idler. Is it turning smoothly or with pauses when printing infill or perimeters? When printing a straight line, it should not pause in the middle of the line. In corners it may be that the extruder pauses, depending on the Vxy-jerk setting. It can happen that this spring applies too little pressure or too much. See if you can adjust the tension.
2. If at the end of the print 2mm is retracted, it's a good idea to feed 2mm before you print. I use 5mm as I'm using a bowden setup.
3. Certainly a good first project! There are many designs to choose from or design your own.

1.
Do you use a graphic LCD (12864) on a delta printer with an arduino Mega?
It could then be an extreme case of stepper stuttering from processor overload....

2.
Also you don't have a fan shroud for the hotend and the heater block isn´t insulated. This can be the cause for the clogging.
I took some cardboard between heaterblock and heatsink and painter tape to DIY my own fan shroud.
3.
Some people use an empty spool to transfer new filament to it. They sample-measure filament thickness over the whole length and as a side effect, discover tangled filament, before it´s used.
-Olaf

1-
Imqqmi:
the heads is moving pretty smoothly I think, it moves at somewhat constant speed or no real variations that are observable. What I'm observing is that the extruder motor stutters on the initial print lines to make the foundation. On the successive layers, it is much more consistent and it seems to be somewhat related to the speed of the head itself. When it is going at speeds higher than 20mm/s it seems the feeding extruder is not able to push and will stutter causing the beads. Does this make any sense?

OLampe: I am using an LCD screen indeed. How can I troubleshoot and see if this is the problem? would disconnecting the screen complete the test?

2- Ah I see, so adding the 2-5mm that is used at the end of the print in the startup instructions? I will add that. Then if I just E-stop, I should be retracting approximately that much by hand, yes?
I'll look into the fan shroud as well. I currently also have the fan running 100% of the time, perhaps having it be on-off would be better. It's one more component to have to nurture though.

When the head moves smooth, it is possible your extruder driver is faulty or the 3 microstep-jumpers underneath provide bad contact or are missing.

Disconnecting the graphic?? LCD won´t help, you´d have to disable it in firmware or reduce "segments per second" from 200 to eg. 150 in configuration.h.
A character LCD like 20x4 will be less problematic with delta.

The problem with Arduino based firmware is, you have to have a valid configuration.h ( from your vendor ) to change one variable or you´d have to go through the whole file and set everything from scratch.
That´s why I recommend this as last step, when everything else failed.


-Olaf

That makes sense, if it doesn't run smoothly at slower speeds it may be that you need to hack your stepstick. If you have a board with separate stepper drivers and you're using a A4988 you can short R4 if the value on it is 103, ie 10k ohm. It will go into mixed decay mode and runs smoother at slower speeds. The 8825 has a similar hack. You can find more info on google.
I replaced the 8825 without hack with A4988 with hack already in place and it improved print quality visibly.

If you want to check without lcd you'll need to recompile and upload the firmware. Just disconnecting the lcd doesn't help.

I've gone and shorted out the R4. I see that the effect I'm supposed to see is that the drivers are supposed to smoothly push out the filament instead of having a discontinuity in the voltage/current when crossing the 0V mark. It didnt seem to have done much of a difference.

I've also removed the LCD from the configuration.h and decreased the segments per second to 100.

I am still seeing a beady trace. I'm thinking maybe the motor axle is slipping on the filament. I've played with the tension (manually), it didnt seem to change much. I'm thinking maybe the teeth are dirty because they've scraped off too much filament and no longer have good contact.

ABout the fan shroud you had talked about, I see a lot of people making a fan shroud to focus the air on the hot end instead of the heatsink part of the extruder. Is that what you mean?

Quote

ABout the fan shroud you had talked about, I see a lot of people making a fan shroud to focus the air on the hot end instead of the heatsink part of the extruder. Is that what you mean?

No, what you saw was the attempt to cool the heatsink and the print below the hotend with one fan.

I almost don´t dare to ask: have you checked the filament gear and idler for unregular movement? eg. the hole in the gear isn´t centered or too big for the shaft?
Is the grubscrew tight?
Is the idler bearing broken?
-Olaf

Edited 1 time(s). Last edit at 09/29/2015 11:33AM by o_lampe.

ah............ I had a jam in the hot end, took off the hot end, put it back on... broke the barrel! So no printing for a while

However, I will tell you that indeed the filament gear and idler are doing irregular movement, they are stuttering. It nearly looks like the filament is slipping on the teeth. This gear has teeth all around it, but this means the gear is flat and has less contact than it could have. I went and ordered this one instead
[i.ebayimg.com]

I'm thinking though that it is because the temperature of the hot end may be too low so it is not melting the filament fast enough.

The idler bearing does not look broken. The grubber screw is tight.
It is possible that maybe I am not powering the power supply enough to maintain the heat of the hot end to melt the filament.

We will know in a week when I get the replacement hot end.

Bad luck for you, the linked hobbed gear won´t work for your extruder. You´d have to print a direct drive extruder that matches the smaller diameter of the gear.
It is important for good grip, that the filament feed is in line with the gear.
If you´d try it with your extruder, the filament would be pushed in an arc against the gear, providing even less contact area as you´ve now.

Can you add more pressure to the idler bearing to provide better grip?
-Olaf

I thought this would be a good opportunity to test the gear since there's no hot end we remove that from the equation.

The PLA fed very nicely and smoothly. The extruder motor does not stutter.
I'm really thinking the hot end was unable to provide enough heat to melt fast enough. I usually set my hot end to 200C according to the internet that is the right temperature. Should I be increasing that? It is also possible I'm trying to move too fast and the feed rate would be in proportion.

Edit: I test a simulated print without hot end and the extruder pushed out the PLA filament without any stuttering. I think its somewhat clear that the nozzle is not heating fast enough to melt the PLA. Is it not hot enough, i.e. need to increase the temperature--> does setting the temperature at 200C sound right? or it is not heating the nozzle back fast enough, i.e. need to change the PID parameters to turn the heat of fast enough? --> wouldnt make sense because temperature controller wouldn't react this fast anyways.

Perhaps reducing the print speed is still the thing to try.

Edited 1 time(s). Last edit at 10/01/2015 01:00AM by djtrance2.

200C sounds right, but how certain is it, you actually have 200C when it is shown on the display?
There are so many different thermistors, you never know, what you get....
The best way to find the sweet spot for your filament, is to extrude manually ( when your hotend is functional again )
-Olaf

Edited 1 time(s). Last edit at 10/01/2015 03:03AM by o_lampe.

I might be late to the party but your hot end fan is backwards.
It should blow air onto the heatsink.



Also a shroud helps.
look up e3d fan shrouds
e3d online

Also for pla the temp should be between 180 and 210.
I never had to go higher then 190 or 195. Clear colors normally need less temps so i run them at 190c.

Also if you dont have a pla cooling fan (fan aim at the nozzle tip) your part will melt while printing and your square parts will be roundish.

Interesting remarks, thanks for those.

So you need 2 fans? (or we could have 1 fan with a shroud that points partially to the PLA and the rest to the heatsink).
I did notice that printed parts were not very sharp, perhaps that would help.

If the temperature of 200C is correct (and then again, how would I know it is correct?), why would the melting not keep up with the extruder making it stutter?

I think I might have found the issue here, Maybe it was obvious, but I never touched this parameter. M92 E94.5 would set the steps/mm for the Extruder to 94.5steps/mm would give me approximately 100mm for a call to g1 e100. Is there an actual value that others have found for this?
My extruder was set to 439.5 steps/mm. This would have caused the stuttering because the extruder was trying to push 4.7x more filament than it was supposed to! I will know better when I get the new nozzle and test this out.

Extruder steps is usually set in the firmware.