Intermittent extrusion?

Hi all,

I've been able to resolve problems and improve print quality of my MakerGear Prusa Mendel successfully for about 2 years, but I've been troubleshooting this bug for what seems like six months, so I'm hoping you can tell me that I missed something obvious that I can fix and get back to printing my Tantillus

The attached photos do a pretty good job describing the problem. After the first few layers, the nozzle starts depositing plastic very intermittently (photo 4 shows a print stopped while it was laying down one of these messed up layers on top of earlier well-formed ones). I haven't identified an exact pattern, but if you look at it long enough you start to see things. This problem appeared gradually, I had been printing for weeks without issue and then slowly I started to see gaps intermittently in infill, then more regularly, then in shells, and finally to what you see here. I print almost exclusively with PLA, between 180 - 200C depending on vendor and color.

I've tried a lot of things to resolve this (I'll include a list at the bottom of this post) and while I'm able to change various aspects of the print, this problem has persisted throughout all my testing.

I'm not really sure what to try next, the only ideas I have at this part amount to swapping out parts for new ones, and I'd rather avoid doing that randomly since I was hoping to spend my printer allowance getting a second machine on-line instead of upgrading this one.

Machine details:
MakerGear Prusa Mendel, many modifications but of particular interest may be a customized J-Head (using ceramic heater instead of power resistor, which worked well for almost a year before this problem showed up). Always-on fan cooling the J-Head barrel, secondary software-controlled fan ducted toward output area.

Here's a list of things I've tried to resolve this issue:
Thoroughly cleaned nozzle, barrel & extruder (disassembled, re-wired, electrical tested, re-calibrated)
Drive gear (stainless) tested for wear, clog, etc.
Idler bearing (608) examined for wear, damage, etc.
Idler pressure checks out
Replaced extruder body (was warn from filament friction)
Different filament (Mostly PLA, but different colors, vendors, age, etc.)
Updated Marlin firmware & recalibration
Replaced extruder stepper driver
Changed extruder "channel" on RAMPS board (E1 instead of E0)
Different/bigger power supplies (both mains and battery power)
Different environment (basement, garage, upstairs, outside, different seasons)
Different host software (Printrun, Cura, Octoprint)
Different host computers
Different slicers (Cura, KISSlicer)
Different models
Different speeds (from 15mm/s to 150mm/s)
Bed tram
X & Y axis tension & friction adjustment & tested

Have you tried upping the temp? Your thermistor may be aged/worn. What is your retraction set at? Have you tried lowering that? Wear on the internals may increase friction, and retraction is the main cause for jams in my personal experience, although not at all a general problem.

---

Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

Thanks for the notes MrDoctorDIV,

Right now retraction is disabled, but I've tried it both off and on (and various degrees of on) with the same result.

I'll give higher temps a try (200C+) and see what happens, thanks for the tip!


- Jason

Hello jjg,

Here are some things you didn't tested (if I read correctly your list), and that could be very easily:
Changing the CAD software. We don't know if the visualisation of the G-code is correct. Maybe the CAD software that you're using produces some meshing bugs.
Changing the USB cable. Well, you changed the PC, but have you changed the cable?
Printing directly on SD card. That will induce that the USB interface processing is messing around.

This seems to be a interesting problem, I'm curious to see its solving.

Hold on jjg

Edited 1 time(s). Last edit at 08/29/2014 04:17AM by thib88.

CAD software is mostly OpenSCAD, but I've tried models I've created myself in Tinkercad, and models created by others from other software as well. Good call on the Gcode visualization but the models look correct in Gcode visualization as well.

Many different USB cables tried

I'd like to try printing from SD to eliminate the computer/host software/etc. as variables but unfortunately I don't have an SD adaptor for my RAMPS board. Maybe I should pick one up though since it would come in handy and might help isolate the issue...

The more I read and think about this I'm starting to suspect there may be some damage inside the barrel that I can't detect by looking inside it. I'm going to see if I can track down/cobble together another hot-end (I'll need one for the Tantillus anyway) to swap for the one I'm using just to try and identify/eliminate the hot-end as a suspect.

Thanks thib88!


- Jason

Hey all,

Just an update, I swapped out the old jhead for an E3Dv6 and the problem went away, so it's either in the old hot-end or an interaction between it and the rest of the system.

I'm planning to dissect the jhead and see if there's any explanation there, but first I'm going to use the new hot end to finish printing a spare printer