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oozing and stringing

Posted by clogs51 
oozing and stringing
April 27, 2015 05:45PM
I recently bought a few reels of filament from a different supplier than my usual one.
This filament causes severe stringing and oozing of the hotend.
I tried lowering the temperature to 160 degrees,but got the message "cold extrusion prevented" in pronterface.
I had changed the temp setting in all the slicer and firmware settings,so why did it still refuse to extrude?
In any case,would lowering the extrusion temp actually work?
I also noticed "flecks" of pla on otherwise smooth surfaces.I didn't have any of these problems with my previous filament,
but as i bought 4 reels of the new stuff,would like to be able to use it.
I went back to my "old"filament,and the problems went away,so it's definitely something to do with that "new" filament.
Re: oozing and stringing
April 27, 2015 08:14PM
Marlin has a failsafe to prevent extruding at cold temperatures. The threshold for what's cold is hard-coded... to change it, you would have to edit the source code, compile, and re-flash your Arduino board.
Re: oozing and stringing
April 27, 2015 08:41PM
You could also send an M302 code to the printer in the start of your G code by putting it in start codes of your slicer. That will allow the extruder to feed even if the hot end is cold. It is generally not a great idea to override safety interlocks but if you just want to experiment it will be fine. It doesn't involve changing any firmware settings so you can revert to cold extrusion prevention by just removing M302 from start code for subsequent slices. I have used M302 previously to test the extruder drive when building the machine.

My Prusa Mendel i2 inspired Repstrap with welded steel frame: [youtu.be]
And my Smartrap derived Briefcase 3D printer: [youtu.be]
Re: oozing and stringing
April 27, 2015 11:32PM
Well kickamamoocow!
I remembered I had changed a blown thermistor on the hotend a couple of weeks ago.
I ordered a few Semitec ones from hotends.com,but decided I would try one of the el cheapo chinese ones I got from Alixpress in the meantime.
I found out through trial and error that they were 1k pull-up,rather than the more common 4.7k.
Accordingly,I set the thermistor code in Marlin to 51,and carried on.
In hindsight,I should have known something was amiss when I saw a wisp of smoke coming from the nozzle.
Turns out,these chinese thermistors are hopelessly inaccurate,causing the hotend to run much hotter than the temp shown.
I had forgotten about this,until a parcel arrived today,containing my Semitecs from hotends.com(Great service,can't fault this chapsmiling smiley).
I changed the thermistor for the semitec,reverting to no.5 in the Marlin list,and hey presto,no more oozing or stringing!
Nothing wrong with my "new" supply of filament at all.
The moral of the story is :don't buy sensitive electronic components on price alone.
I have 9 chinese thermistors in a drawer,and there they will stay.Or maybe transfer them straight to file 13grinning smiley
Re: oozing and stringing
June 06, 2015 02:05AM
I've had some intermittant extrusion consistency issues. Typically representing as banding in my vase prints.
Found my thermistor had come adrift from the hot end under my cooling shroud(fixed now), but also, watching temperatures, they vary considerably (over around 6 deg C) in a cycle during printing that matches my banding on the vases.

So I'm about to run the PID tuning algorithm and modify my firmware settings for better consistency.

Google repetier pid gcode if you need.
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