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Extruder issues with ABS

Posted by BoByS 
Extruder issues with ABS
December 01, 2015 10:52AM
Hi, folks!
So, my situation is as following (it's driving me crazy and I really hope for help!) -> More than a month ago I've upgraded my Prusa i3 3D Printer to 1.75mm Bowden extruder (printed by myself) with E3D v5 (Chinese) hotend with great results. My old setup was with Wade's geared extruder and 3mm filament. The problems came a little bit later. The idea is that my extruder motor is skipping steps (the famous clicking sound) and grinds the ABS filament.
I managed to make it to work with PLA - now it's skipping 1 or 2 times in a print - mostly because my heated bed is bowing on the center and when the hotend is printing on the borders of the bed - it's skipping a few times (if it's 0mm in the center, it's +0.1 or +0.2 on the borders). I'm printing PLA with 235 deg hotend for the first layer and 230 deg for the rest of the print.
Well...with ABS it's completely different - I've tried to increase the spring tension on the extruder (starts to grind the filament and skipping like crazy), it's filling the PTFE tube with dust and the filament is sticking in the tube (in PTFE tube, like...really?) I have tried to decrease the tension of the spring and more heat to the hotend (250 deg - I'm really afraid to go beyond this value) - still skipping like crazy. I have tried different driving gears or new extruder that is with less distance between the bearing and the gear - still nothing. The stepper motor of the extruder is with 0.48 Nm torque (my other motors are 0.4 Nm so it's bigger motor) and the stepstick is adjusted to it's maximum (or I'll never print with PLA, too sad smiley ). Any idea?

P.S. #1: When I push the filament thru the hotend - it's going freely. When I lift the nozzle and extrude some filament - skipping, jamming, etc. and almost no extrusion.
P.S. #2: It's not a problem for me to print another extruder with gears - If that will be the solution of my problem...
P.S. #3: The only thing that is comming to my mind and I didn't do is to try with different ABS filament manufacturer (my PLA and ABS are from one manufacturer - they're not the cheapest one (well...like mid-range)!).

These are the things that I have:
1. Autobed leveling with aluminium heatbed and inductive sensor.
2. OD 4 / ID 2 PTFE tubing (will upgrade to 4/3 after Christmas).
3. Prusa i3 printer with Marlin software - E jerk is 5 in Marlin if that helps.
4. The print speed is 30-40 mm/s.
5. Big mottor with almost maximum (let's say 95%) ot the capacity of the stepstick - I have a huge active cooling on top of my RAMPS board and the motor is COLD while working - it's not a problem to handle it! -> Here, I've wrote a small program to calculate the Vrefs of the stepsticks and it's showing even bigger value of that -> 1.8V for that particular motor and I'm running it in 1.36-1.42V range (Last time I've turned the pot a little bit to lower the value and I didn't measure it).

Best regards,
Re: Extruder issues with ABS
December 01, 2015 07:33PM
If you work with retraction you need proper settings for the retraction speed and distance to start with.
But the main problem with e§d clones is the quality of their finnish.
In a perfect world we have extruders that won't damage the filament, sadly in our real world that is not possible.
ABS is quite soft but not flexible, so if it flattens in the extruder it will stay flat - check the roundness of your filament before entering the extruder and compare to what comes out (without the hotend of course).
You want the pressure on the bearing so that the filament is still transported safely but with the least pressure possible.
The hobbed bolt needs to grab the filament without cutting too much into it - especially those grooved bolts tend to chew the filament sides and produce a lot of dust this way.
I use only 3mm filament and 3.2mm nylon on a standrad wades extruder with Nema17 motor...

Take the nozzle off your hotend and use fine sand paper rolled up to remove all grooves and corners in your hotend.
Pay special attention to the area where the heat break is, usually there is a little gap and if the diameters don't match perfectly it is the place where filament gets stuck.
If you use filament that already went through the extruder you will feel the resistance of the damaged areas, once sanded and polished it is difference like day and night.
Re: Extruder issues with ABS
December 02, 2015 01:08PM
Thanks for the informative reply, Downunder35m!
Basically I'm assuming that my retract settings are somehow good for that extruder. Can you define good settings? They are a little bit harsh (3mm at 100 mm/min) but...well...it's not skipping too much on the retracts. Thanks for the info about the bad quality hotends, it's clearer now. I'll try to play with the extruder and the hotend (saw a video on YT about that) and if no positive effect occurs - I'll buy the original one.
Actually I saw something weird in my hotend - there is a PTFE tubing inside of the heating barrier. I can't find proper info but I think that in the original one, there isn't tubing? (Assuming that the Chinese manufacturers are making identical parts for 3mm and 1.75mm filaments and compensate the difference between them with that PTFE tubing).
Many times I was hoping that this "battle" will end soon...but this is just the beginning. smiling smiley
Best regards,

Edited 1 time(s). Last edit at 12/02/2015 01:09PM by BoByS.
Re: Extruder issues with ABS
December 02, 2015 09:15PM
Some hotends come with a liner inside the cold end but that should stop at the top of heat break as otherwise it can fail under high temps.
Unless you use very soft filament it should not matter too much if the liner is removed, flexible filament won't work without though.
Good settings are very hard to suggest as there are too many variables.
Best IMHO is to start slow, like 20mm/s and while going slow to do the finaly tweaks and adjustments on the hardware.
From there you work your way up until either the hardware or filament fails and crank back a bit.
Moving mass is a factor not to be misjudged!
A X-axis with direct extruder might have some weight but that is nothing compared to a big print bed with heated bed and glass plate.
Same goes for those springs holding the plate - at higher speeds they can cause the platform to swing at the start and end of a move usually resulting in a wave pattern staring from a corner.
Really the main thing is a reliable extruder / hotend combo.
You simply don't want to get failed prints while tuning because something jams or blocks.

If you want to save some money keep your hotend.
From the heat break remove the thread on the top 3mm - this will allow for a better fit in the cold end.
Get a teflon liner that matches your filament but provides a quite thick wall, like 4mm outer diameter.
Drill the coldend out down to where the heat break stops and make a test hole into something else first to check that the teflon liner is a tight fit.
The liner should go as high as possible, e.g. for a direct drive system all the way up and for a bowden all the way into the connector.
This way you have a smooth surface all the way to the heat break and if that is sanded and polished you should have no problems anymore.
As a hint: For 1.75mm filament use 2mm ID liner, for 3mm filament use 3.2 or 3.3mm ID liner.
Re: Extruder issues with ABS
December 06, 2015 04:34AM
Thank you again for your reply! You're really helping me a lot!
Yesterday I was fighting with the ABS filament again (now with a filament from different manufacturer and it's ABS Print Plus). I've tried the extruder without the hotend. No problem of pushing it though. I adjusted the spring tension and now the extruder is pushing the filament almost without deformation (at least my calipers couldn't measure a difference so I assume that it's in the calipers' error - 0.1mm). The 20x20x20mm test cube came really good. I think the result is even better from that with PLA but it's really hard for me to compare them. The brim is a standard for my printer - 2mm. If I don't put brim there is like 80% probability that the corners will wrap with something like 0.3-0.4mm from the table.
I will continue to fight with my old ABS spool - after all, I've already pay for it and it's awesome blue color that I really want to work with... smiling smiley

So my conclusion for now:
1. The extruder is OK for ABS prints.
2. The tension of the spring is also enough to push it almost without deformation.
3. The problem isn't in my PTFE tube from the extruder to the hotend.
4. The hotend works for now. If it fails again I will disassemble it and mod it - I don't actually want to do that now because it took me some time to adjust everything in my printer. The cable management is also good and I'm happy with it.

Best regards and happy printing.

Edited 1 time(s). Last edit at 12/06/2015 04:35AM by BoByS.
open | download - ffa789bc27559ce08c09185d52ea25835021b8bf51cd7028c8442fc787f5596a.jpg (39.1 KB)
Re: Extruder issues with ABS
December 06, 2015 07:03AM
It really sounds like the hotend temps aren't high enough. If you have the wrong thermistor selected then the displayed temps will be wrong.

Have you tried either lower print speeds, or higher hotend temps?

Also double check your thermistor settings.
Re: Extruder issues with ABS
December 06, 2015 03:11PM
Thanks for your suggestion, nebbian!
Yes, my thermistors are pretty crappy but I have measured them with IR thermometer tool. When my printing bed is on 55 deg, the tool shows 51 deg. When my printing bed is on 105 deg, the tool shows 96 deg. Everything is in the limits, because my thermistor's error is 8-10%. I'll do my best to measure the hotend temp as well. It's hard to do it with a big tool like the IR thermometer.

The fight continues: I was able to adhere the ABS with some gluestick over the blue painters tape. Now, I can print with a minimal raft (like 1 mm). Some of the layers have holes and when I put a knife in them I can able to detach that part from the main body. I have to play with the temperatures once again and make sure that my printer is in a constant temp environment (like make a box that will cover it or something like that).

Best regards!
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