Print problem: inconsistent extrusion

Anyone know what's happening here? This is an orange Faberdashery PLA print of a Settlers of Catan piece. 0.35mm nozzle, 0.25mm layer height.



This problem occurs at normal speed, but not at first layer speed - this screenshot is of a print where I set the first layer speed to 100% so the problem would reproduce itself quicker. Notice the lower layer has printed consistently, albeit with seemingly not enough plastic, as the lines have separated - see far side.

I read online that inconsistent extrusion could be due to a too-low temp, so the version in the screenshot has the temperature raised to 205. However, this made it noticeably worse. (My standard temp is 185, and I'm using Slic3r.)

It doesn't feel like my extruder is missing steps. During this print, I tried slackening off the filament clamp thing and putting it back, but it didn't seem to make any difference.

Possibly relevant: I recently checked my extruder and found that if I heated it up to temp and told Pronterface to extrude 10mm, the filament moved significantly less. So I adjusted the steps-per-mm value in Marlin until that was correct. This seemed to be OK for a while - I've managed to print test pieces since then. Although, as one might expect, one does seem to be getting less plastic.

Gerv

Gerv,
I had something very similar and ended up with a blocked JHead. Although it may sound too high - try the print at 220C and see how that goes. Nothing lost if it doesn't cure things but this temperature is my regular "start from here" temperature when printing with PLA on my Nophead Mendel90 kit machine
Alan

EDIT: Think I jumped in too quickly - anxious to contribute and recognising the problem in Gerv's attached photo - RichGain's suggestion below, of cleaning the hobbed bolt teeth seems the best starting point - if it ain't gripping properly, extrusion is going to suffer.

Edited 2 time(s). Last edit at 02/28/2013 10:07AM by Alzibiff.

Might also be worth checking that your hobbed bolt has clean teeth.

In my experience coloured PLA won't print below 200C and most colours need at least 220C. Start at 220C and only go lower if it starts to run out like syrup and wont span the gaps between sparse infill.

I don't know where the common recommended temperature of 185C comes from. Even natural PLA is very viscous at that temperature. Mendel90 uses its own thermistor tables that are accurate compared with a thermocouple inside the barrel. I think some of the standard tables distributed with Marlin are miles out. If you try to measure the temperature on the outside of the heater block with a thermocouple it will read 20-30C low. Not because the outside is that much cooler but because it only heats one side of the thermocouple. To get an accurate reading it needs to be jammed in a hole that is closed with a punch. I have had some success with surface contact if I insulate the outer side of the thermocouple so that it isn't cooled by convection.

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[www.hydraraptor.blogspot.com]

I print all my PLA at 210°C.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

I worked out what it was; it turned out to be that the extruder idler was too _loose_. I tightened it right up again and things are now much better.

The hobbed bolt does have clean teeth, but those who suggested that were on the right track - I had a problem of inconsistent feeding.

I don't know what temperature my hot end is actually at when I print, not owning an IR temp gun, but I've found that setting 185 degrees in Slic3r seems to work OK. 205 had it pretty liquid. But I'll experiment.

Thanks everyone!

Gerv

This thread was very helpful.

After tightening the idler, increasing the PLA extruder temperature to 220C, and then recalibrating the extruder steps it now produces good consistent prints.

Thanks all!
Globster

Quote
nophead
I don't know where the common recommended temperature of 185C comes from. Even natural PLA is very viscous at that temperature.

I have seen specifications for the various formulations of PLA e.g. 4043D etc. with 4043D quoted as printable from 160C upwards and 4033 printable from 190C upwards.

Apparently 4043D is not sold into China so any filament originating from there is likely 4033. The 4043D I purchase from Reprapsource.com does print well at 185C and oozes significantly above 190C. This assumes a printing speed of 40-50mm/sec and for higher speeds you can increase the temperature.

Regards,
Neil Darlow

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

That quote was from more than 2 years ago. In October 2013 I added the silicone tape around the heater block and added the hole in the fan duct to keep the top of the hot end much cooler. After those mods 185C works with the village green PLA from faberdashery supplied with the kit and gives more consistent results than higher temperatures.

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[www.hydraraptor.blogspot.com]