"Brittle" PLA prints - layers not sticking together.

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(Alex Wiebe) #1

“Brittle” PLA prints - layers not sticking together. Printrbot Simple w/ aluminum extruder and bed.

A number of my recent prints seem to be brittle. Since I changed too many parameters, I’m looking for wisdom of the crowd to help narrow my troubleshooting :slight_smile:

The symptoms are:
a) sticking harder to the tape on the bed and therefore breaking when removing.
b) when printing a tube that is narrowing, sometimes the filament doesn’t stick to the previous layer and strings across the gap
c) basic destructive tests show that final product breaks / separates at layers with surprising ease.

Variables that changed:

  1. ran out of white PLA, switched to blue (seems to be more translucent)
  2. switch host OS (from XP to Ubuntu) which led to
  3. switched slicer from Slic3r to KISSlicer which led to
  4. different parameters - potentially many differences, but 2 major differences are
    4.1) lower printing temperature (185 at first, now 190 vs 200)
    4.2) slower printing speed (haven’t studied where the speed is in the slicer configs, but elapse time is close to 50% longer)
(Richard Mitchell) #2

I’d look at the temperature first. Helped when I had a similar issue.

(Stephanie A) #3

Some formulations of filament have less desirable properties than others. Moisture can also make this worse. You need to properly calibrate the filament diameter and temperature to the new filament as well. It’s more apparent when switching colors or suppliers.

(Daniel Porter) #4

I experienced this when I was testing printing at lower temperatures… the lower the temperature, the less layer adhesion I had!

(Joseph Chiu) #5

First of all, make sureyou are extruding enough material.

If you are under extruding, it simply will not stick well together.

With KISSlicer, I have found that specifying nozzle size exactly the same as the actual nozzle size was not working well enough for me. Upping by about 10 to 20% (at least for infill) was key to improved adhesion. (This is separate from the issue of extrusion amounts, which is a factor of the filament diameter and the multiplier). Set your z offset to a slightly positive value (0.05 to 0.10mm) to address the sticking issue.

Also, don’t be afraid to go a little hotter. Taking PLA up to 210 on most hot ends is fine. Just make sure you are getting enough plastic, first.

(William Frick) #6

Slic3r is available in linux flavour so you could return to your old[familiar] settings. If you have an old gcode file from your XP days you could also try that is you have the same material.

(Daid Braam) #7

Could be that your new material has more moister in it. Printing it a bit hotter would help in this case. PLA absorbs moister from the air, which influences the print in different ways.

(Brook Drumm) #8

Higher temp… 205+ , correct filament measurement and high quality should do it for you. First layer height is key too.

(Alex Wiebe) #9

@Brook_Drumm @Joseph_Chiu Interesting that you both mention 205-210C. I was printing at 205 first layer, 200 thereafter - but after an hour or so it would jam. The last long print was at 190C and it ran for nearly 3 hours without a jam. I do have a fan now secured to cool the extruder, so I may attempt higher head temps.

As for moisture - I suppose that is possible, our house is somewhat humid at the moment (50-60%). I took the roll out of it’s sealed bag and was printing within 24 hours. What is the open shelf life of PLA?

(Brook Drumm) #10

Hearing your temp was right changes my theory. Sound like a clog. First, try the manual method. Push plastic in, pull it out quickly and snip off a couple inches. Repeat. Watch for debris or a change in required pressure to extrude. If it gets easier, you cleared an obstruction. If it’s still relatively hard, try cleaning the tip.

Get it hot and remove the tip, while the plastic is still hot in the tip, get a cold piece of plastic and smush it in there then try pulling out the blob. When finished, you should be able to see light through the tip. Put it back on while hotend is at temp-- careful!

This is normal maintenance stuff.

Only other idea, spring tension is off.
Filament is too big or swollen in areas and it works when it’s smaller diameter, fails when it goes out of spec to a larger diameter.

Also check set screw on drive gear and potentiometer on the E driver on the printer board.

Ok, now I’m reaching… Loose / shorted wires in hotend?

Print speed way too fast? Too fast for certai. Areas of the print- slic3r settings?

Good luck and keep us posted.

(Camerin hahn) #11

@Alex_Wiebe technically it Vann absorb moisture in a couple of hours, but my findings have been this adds bubbles in the print, not delamination.

Higher temps do work better, until you get too hot and the heat travels up the hot end.

(Joseph Chiu) #12

If you have an extruder where you can easily disengage the drive gear, try to see if you can manually feed filament at the time it jams. If it still feeds smoothly, your problem is probably not a clog from debris, but instead may be the result of other factors like heat traveling up to the input feed causing the filament to buckle, or you have overextrusion causing the layer height to go far enough above nominal to backpressure the output from happening (though unlikely given your delamination issues), or you hit a spot in your print with excessive retractions and you’re chewing up your filament, or the retraction is pulling back more molten plastic which is cooling onto the thermal tube and then forming a plug. PLA in particular seems to need the hotend to be hot, and everything else to be not – so that extra fan should help if you’re blowing air to the top sections of your extruder.