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New to ABS - Filament Slips After Printing 20-30min

Posted by gebelke 
New to ABS - Filament Slips After Printing 20-30min
February 09, 2016 07:42AM
I am new to printing ABS but have printed about 5kg of PLA with excellent results (at 60mm/s). I am printing Orange Hatchbox 1.75mm ABS on my Frankenmax (design was based on MendelMax 2, but lots of design changes by myself in CAD to improve performance and now 90% aluminum) inside of an insulated enclosure (~0.5m x 0.5m x 0.75m, 1" with extruded polystyrene sides ). I have no problems with the filament sticking to the glass coated with a bit of glue stick, which starts at 86degC and drops to 80degC on the 2nd layer. The enclosure will get up to 50degC with only the bed at 90degC for ~45min.

My problem arises when I print for longer than 15-20min. The best way to describe it is that the filament gets soft and strips on the Mk8 extruder gear. The only way for it to continue printing is to increase tension.

I recently changed out the extruder from a spring tensioner to a bolt/o-ring, extruded and tightened the bolt until it started extruding, then gave it another 1 full revolution tighter. The reason for this change was the spring was not strong enough to reliably extrude without slipping, so I wanted to switch to something that could have more tension on it and rule that out. The extruder is a direct drive Makerbot 2 roller/lever/base system. The nozzle is an E3D (with 30mm heatsink cooling fan) and two nights ago, I took out the PTFE liner in the heat break to inspect it and it was perfectly fine, no restrictions on ID, or melted plastic remaining. I performed a few atomic pulls and they all came out with a great shape, with sharp nozzle and about 1.5mm worth of 0.4mm diameter filament.

Last night, I printed a small part that took 7min at 100% infilll that turned out amazing. I thought the problem was fixed, so I decided to print another part that should have taken about 45min and it failed ~20min in. The failure was that it wasn't spitting out plastic. As soon as I tightened the extruder tensioner bolt another turn, it started extruding plastic again, but it was too late to save the print.

Here are my print settings in Slic3r:

Layers: 0.2mm
First layer: 125%
Perimeters: 2
Solid Layers: 3 (top), 2 (bottom)
Infill: 100% rectilinear
Skirt: 2 loops, 3mm away from part
No support

Speeds: 20 mm/s max

Temp: 240
Nozzle: 0.4mm
Bed: 86 (first), 80 (rest)
No Cooling

Retraction Length: 2mm
Lift Z: 0
Speed: 20 mm/s
Minimum travel after retraction: 0.2mm
Retract on layer change

My thoughts are that filament is getting slightly soft from the 30-40degC enclosure temperature (spool is outside of the enclosure) and then there isn't enough tension on the extruder. Alternatively, the extruder motor could be heating up causing the hobbed gear to melt the plastic and slip. Tonight I plan to remove the printer from the enclosure and see if that helps any. If that fails again, I will point the PLA turbo cooling fan at the hobbed gear in an attempt to cool that should it heating up the filament too much before it goes into the heat break.

I only have about 1-1.5 hrs per night to experiment with changes, but after spending the last 4 days on it, I'm getting a bit confused as to where I should focus my efforts now. I do have access to another printer should I need to print out replacement parts, but mechanically speaking, everything is rock solid and there is no creep in the printed parts.

Here are some relevant settings from firmware (Modified Marlin firmware on RaMBO board):

#define DEFAULT_AXIS_STEPS_PER_UNIT {80.143,80.184,1594.737,97.01}
#define DEFAULT_MAX_FEEDRATE {500, 500, 5, 25} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {1500,1500,100,10000}

#define DEFAULT_XYJERK 10.0 // (mm/sec) - Default - 20.0
#define DEFAULT_ZJERK 0.2 // (mm/sec) - Default - 0.4
#define DEFAULT_EJERK 5.0 // (mm/sec) - Default - 5.0

#define DIGIPOT_MOTOR_CURRENT {135,135,135,135,135}

Edited 2 time(s). Last edit at 02/09/2016 08:08AM by gebelke.
Re: New to ABS - Filament Slips After Printing 20-30min
February 09, 2016 12:10PM
The pinch wheel tension on the extruder should be so high it almost crushes the filament. You want the teeth on the drive gear to bite deeply into the filament and if the nozzle jams, the extruder motor should skip. It should never chew a divot into the filament. If it chews a divot, the tension isn't high enough, period.

ABS will not soften at 50C. You could have a problem with heat creeping up the hot-end, but if you were able to print PLA, that's not likely. PLA is usually much more sensitive to that sort of thing because it does soften at low temperatures.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: New to ABS - Filament Slips After Printing 20-30min
February 09, 2016 12:23PM
Thanks for the reply, the E3D heatsink feels cold to the touch even after 12 hours of printing at 215degC (PLA), so I really don't think it's from the nozzle.

The extruder motor is a bit hotter than with PLA, so I may throw a fan on the hobbed gear to rule it out and ensure the gear isn't softening the filament (which is very easy to redirect PLA cooling fan to the gear). Though if that's the case, I'm wondering if there's too much current going to the motor (set at 135 now out of 255).

Is there an easy way to determine how much tension? Or just keep cranking the tension up until it prints. If this was the sole cause, why would an 8min print work, but then a later 20min print fail. That leads me to believe it is more likely a hot motor softening the filament, wouldn't you agree?

And at the amount of time the printer is truly enclosed, the internal temp won't get beyond 35degC (16min preheat with only bed at 90deg yields 38.1degC air temp), so an overheating RaMBO shouldn't be the culprit either. However, I could quickly rig up a fan to blow on that too. Eventually I'll get a molex crimper and extend the motor wires so I can get the RaMBO out of the enclosure, but at the moment that's low priority and I want to get my printer back online.

Attached is a picture of the tension I have now, printing a new extruder assembly with ABS, the lever arm seems to be going okay (so far), but its also only 10min in.

Edited 1 time(s). Last edit at 02/09/2016 07:48PM by gebelke.
open | download - Tension.PNG (503.6 KB)
Re: New to ABS - Filament Slips After Printing 20-30min
February 16, 2016 06:48AM
the extruder motor should skip.
My extruder motor did not skip, the Wade gear broke sad smiley Used friction welding with a dremel to repair it and used it to print a new gear smiling smiley The repaired gear was so strong that I keept it on the printer until it broke for a second time (serval weeks later)
Re: New to ABS - Filament Slips After Printing 20-30min
February 16, 2016 07:19AM
Yeah, that's one problem with using 3D printed parts in 3D printers... I'm trying to eliminate as much 3D printed stuff from my printer as possible. Right now I'm working on metal versions of the last two functional parts- the X axis motor mount and belt tensioner.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: New to ABS - Filament Slips After Printing 20-30min
February 16, 2016 07:47AM
Well after a bit of finagling, I was able to get it printing decently well. I had to modify the filament tensioner mount to increase spring tension, and now it feeds reliably.

However, now that I'm attempting longer prints (up to 4hrs), other parts are starting to warp significantly since they're PLA. So, I'm rapidly printing those parts out of ABS and considering taking the bigger ones to the engineering department here and have them print them out of Ultem. Because, believe it or not, that would be cheaper than just buying the metal, let alone the time involved for me to take it to the shop and machine it myself from a dxf.

There's always a learning curve with new filaments and ABS seems to be quite a bit trickier than T-Glase or Taulman 618/645.
Re: New to ABS - Filament Slips After Printing 20-30min
February 16, 2016 07:54AM
ABS can be difficult.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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