1 Topic by Kvirre (edited by Kvirre 2013-03-14 13:18:18)

  • Kvirre
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Topic: PLA - ?temperature? problem

Hi,

Backgound
Just bought a spare hotend from solidoodle for PLA printing.
http://store.solidoodle.com/index.php?r … duct_id=59

This hotend seems to be a different model with a Heat Core (boxed-shaped) and pre-drilled for Thermistor to fit.
Unlike the one delivered with my SD2 I ordered where the Thermistor is kapton-taped on the nozzle.

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The problem
I have my extruder-temp set at 170 C and there is blob-buildup and dripping going on, in idle.
The prints look ok (but not good) and smaller parts like a calibration-cube of 10x10x10 mm deforms (melts and collapses) half-way through the print (Bed at 60 C using glass)

The reason I added the background-sections is to inform that I can't establish a good comparison or baseline, since I am using to different hotends (that may read / deliver temperature in a different way)

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Anyone got any suggestions on what i'm dealing with here?

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2 Reply by ronsii

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Re: PLA - ?temperature? problem

Yes, The hot end thermistors will read a little differently, have you checked the resistance of them both cold(same temp) I am not sure if SD used different sensors on older machines or not but I know that you can set for that in firmware.
Try lowering your temp 5 degrees and testing, PLA will drip and ooze more than ABS but if your temp are too high it will really drip a lot.
Sounds like you may be overextruding a little if there is a lot of blob buildup.

3 Reply by Kvirre

  • Kvirre
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Re: PLA - ?temperature? problem

Thanks,

I will try to lower the temp even lower but i'm a bit scared of cold extrusion .... (but maybe there is no risks of damage involved, only skipped gear on filament I guess?)

I'm not to thrilled about using 2 different FW's when switching between hotends.
Does anyone know what offset to expect?

Btw.
I'm ok to do this as a workaround, but could the 2 different hotends have such a large deviation in performance?
Since PLA has been printed using temperatures ~200 C without problems (although not recommended I guess)

So a question back to you that actually use PLA successfully, have you tried higher temperatures and experienced problems as I describe here? Or could this be something else, a clog a broken Thermistor, whatever?

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4 Reply by IanJohnson

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Re: PLA - ?temperature? problem

PLA melts and freezes rather than soften gradually the way ABS does.  It generally needs to be cooled on extrusion to freeze it as quickly as possible.  You can blow a fan on the whole print area and get better results, without causing a problem with layer adhesion the way it does with ABS.  Since PLA is more runny, you will see more oozing on standby, and may need to adjust retraction a bit.

My J-Head has the thermistor in the block, and I run about 190 for PLA and 230 for ABS.  You can get a low end for temp by turning it down a bit at a time while extruding in air.  If you start to see teeth marks from the gear left in the extruded plastic, you'll know you are approaching the lower limit.  With PLA you will get a matte finish at lower temps and a more glossy finish at higher temps.

5 Reply by Kvirre (edited by Kvirre 2013-03-13 16:55:03)

  • Kvirre
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Re: PLA - ?temperature? problem

This is at 160 C ...

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6 Reply by ronsii

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Re: PLA - ?temperature? problem

Looks like a partial clog

7 Reply by Kvirre

  • Kvirre
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Re: PLA - ?temperature? problem

Would you believe that it was the filament itself.

The first thing I noticed was that it broke off VERY easy, so it was prob. a few meters of bad filament.
I had another roll of filament that worked fine, and it did non blobb or ooze in the same way.

Now I reported back to the supplier and will see what will happen.

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