Stringly and brittle

[Atocha]

Had my M2 for about 6 months and I have a love hate relationship with it. It prints exceptionally well until it doesn't. I hit a brick wall with this problem. Ive been printing prosthetic hands for a group in North Carolina for about 3 months. Ive been printing mostly in PLA until about 2 weeks ago. I ran into an extruded jam, ordered and replaced the hot end and nozzle. Started printing again but the finished hands were very brittle. I searched all the usual places and believed that humidity was my problem. I got a de-humidifer and started printing again only this time with ABS.

Ruined another hand. I re-leveled, used a clean sheet of blue tape, purple glue stick and this time I just printed 3D benchy as a test. As the attached picture shows, Its still stringy and brittle. Where did I go wrong this time around?

[Jules]

Could be one or more of several things, unfortunately.....

When you replaced the hotend, did you re-set the Z-Stop and re-calibrate your Z-Offset? (The level wouldn't change, but those values would.)

When you switched to printing ABS from PLA, did you run Cleaning Filament through before putting the ABS in? (If not, you could have a partial clog or plug of PLA still in the nozzle, which might be restricting the flow, causing those strings and the underextrusion.)

When you switched to printing ABS, did you change your printing parameters and reset the Filament Drive Tension?

If I'm incorrect, one of the guys will chime in, but I believe ABS is more brittle than PLA. I know it cracks and splits worse than PLA if it is not printed in an enclosure and kept warm. (PLA is the opposite....it needs to be cooled off quickly.)

If you want to go back to printing PLA, be sure to use some Cleaning Filament (eSun makes it), several times, - to try to clear that new nozzle. (It might actually be clogged now.) The next time it jams, just reverse the filament out and check to see that it isn't stripped before you change out the whole nozzle and hotend. Ninety nine times out of a hundred, the problem is stripped filament and not an actual clog. Unless you frequently switch between different types of filament (like PLA to ABS) without using cleaning filament (or a torch) to clean out the nozzle completely between types of filament.

For stripped filament: viewtopic.php?f=3&t=2694

Cleaning Filament: https://www.amazon.com/CLEANING-Filamen ... g+filament

If you have a V4 nozzle, be very careful and remove the whole hotend before trying to take the nozzle off for cleaning, if you decide to torch it instead of using the cleaning filament. The V4 has a thin neck that will break if you try to unscrew the nozzle while the hotend is still in the machine.

And white filament is by far the hardest color to print - try upping the temp a little. (After you clean out the nozzle.)

Could be any of the above, so just check one thing at a time to see which one it was. Run test cases with the calibration squares until you get it flowing well again, then move on to bigger prints like the benchy.

[Atocha]

Thank You for your replies. I started from scratch again and noticed some anomalies. With my fans removed, I noticed that the ABS filament loads between the gripper wheel and roller and precedes to the extruded. It extrudes for a period of time then just stops. . I bumped my temp to 230 and the same thing happens. I tightened and loosened the filament tensioner with no change whatsoever (I did noticed that at no time did I hear the gripper wheel make any noise like it was slipping. But I can see and feel the indentations in the filament after unloading it). I have disassembled, cleaned and reassembled the gripper and roller system with no change.

I have run cleaning filiment through the machine several times.

Thinking that the hot end my be faulty (installed a new one last week) I picked up some filament and pulled it across the extruder and it melted like butter.

I thought my original problem was humidity but I can take my PLA and bend it back and forth with no breakage.

So now I have this expensive paper weight that sits mocking me.

[Jules]

Isn't 230°C kind of on the low side for ABS? You are probably not melting the filament fast enough and it's jamming. Start with 240° and go up 5 degrees in temp each time it jams.

You did not say how fast you were printing it - you might need to slow it down and give the nozzle more time to melt the filament.

And it really doesn't accomplish much to just randomly tighten and loosen the Filament Drive Screw tension - the odds of hitting it perfectly are not tremendously good. Retract the end after extruding a little bit and compare it against the diagram in the write-up here: viewtopic.php?f=3&t=2694. Too much grip is just as bad, if not worse, than not enough grip. It's very easy to see the indentations if you just hold the end up against a computer screen as a backlight.

[jimc]

yes im confused about what filament your using but 230 is definitely low for abs. 245-255 is usually ideal but may vary with brand. abs will be more sensitive to the tension that pla. too much tension and you will squish the filament out of round causing it to jam in the filament path below the drive gear and bearing. retract your filament as jules said and take a look at the bearing side. does it look flat where the bearing was rolling on the filament. if the flat spot is wide, say 1/3 the width of the filament then you have way too much tension on it. the bearing should only make a slight hairline down the filament.

[Atocha]

Once again your collective knowledge and willingness to share has returned my printer (and pride) to it's original condition.

Thank You for your help.

[Jules]

Yup! Much better!

[3dPrintingMD]

Not fair if you don't at least tell everyone what the problem was and how it was resolved

[Atocha]

Well that didnt last long. I tried printing a prosthetic hand again with horrible results. The print outline is perfect, no adhesion problems. But there are blobs and strings throughout. I have been printing the same exact file for over three months. Except for a change in scaling factor, nothing has changed.

The 3D benchy was the only thing that printed fine after checking all settings, running cleaning filament through, resetting my Z, etc..... I got to the point that I believed maybe the new nozzle was bad. I had ordered 2 last time so I switched them out. Loaded some fresh PLA (I tried several different colors all with the same result) rechecked all my values and just did and extruded purge before continuing. I had to get the temp up to at least 260 c before it would extrude. And then it would start fine with little concentric circles on my bed. It would start extruding squiggles on the nozzle until the weight pulled it down then start extruding larger circles as if it were cooling very quickly. (No fan were on).

I have never, never ever in 6 months had this much trouble with this printer. I have switched between ABS and PLA with no problem. Prior to this, I have barely checked or changed my setting because aside from a level issue, it always delivered.

I had updated my Simplify 3D prior. I reverted back to the old version with no difference.

[Jules]

Okay, the business that you are describing with the nozzle extruding a little squiggle, then a glob forms and drops, and the nozzle then forms a larger squiggle?

That's totally normal, mine does it every single time I prime the nozzle.

What happens is that if you do not clean off the tip of the nozzle when you finish a print, there is frequently a small glob of hardened plastic that just parks itself at the opening, and if you have not let the nozzle pre-heat for long enough on the next print, and you try to purge or extrude too fast, you are actually forcing the plastic out through a smaller than normal sized opening.....and it tends to go sideways for a while.

.... Loaded some fresh PLA (I tried several different colors all with the same result) rechecked all my values and just did and extruded purge before continuing. I had to get the temp up to at least 260 c before it would extrude.

No,no, no.....DO NOT PRINT PLA AT 260°C! Not even for a little while, it will carbonize the PLA on the inside of the nozzle and clog it faster than you can say "Bob's your uncle!".

Maximum "safe" printing temp for PLA is 220°-225°C. If you are trying to print it at 260°, I'm not surprised you are having trouble. Unfortunately, you've likely clogged the nozzle again.

If you are not getting extrusion with PLA, don't take the temp up over 220°. Check for other things like jamming or stripping, but never just increase the temp, it will actually create a problem that didn't exist.

You might need another nozzle. And when you print the PLA, try it at 205°C. You will have less stringing and blobbing, which tend to occur at too high a temp.