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Change from 0.5mm nozzle to 0.3mm .... problems!

Posted by Alzibiff 
Change from 0.5mm nozzle to 0.3mm .... problems!
September 01, 2012 01:35PM
I replaced the nozzle in my ReprapPro Huxley with a 0.3mm version in the hope that this would enable me to print things like gears and the like with greater detail and accuracy. All went fine and dandy at first - extruder was extruding nicely into thin air and my worm of PLA was indeed thinner than it was with my 0.5mm nozzle. (No surprise there really!). However ..... I found that when a print started, it would not take long for it to stop as a result of the extruder no longer extruding - just grinding away at the filament. After several more attempts, tweaking my settings in Slic3r and ensuring my hotend was free of any debris, I was still getting the same problem. It seems that for whatever reason, the filament is getting soft above where it should be, deforming and then wedging itself inside the hot end. The result is that the extruder motor can no longer drive the filament through the nozzle so it contents itself by grinding away at a static filament.
I went back to Skeinforge and for a while things were better - the print process lasted longer but eventually, the same thing happened again. Now ... the fact that different slicers produced different results suggests to me that this problem is a settings problem but I have tweaked what I think needs to be tweaked in Slic3r and don't have a clue when it comes to Skeinforge.
Have any of you guys come across this before me and if so, how did you overcome the problem - what changes did you make other than going back to the 0.5mm nozzle?
Thank you,
Re: Change from 0.5mm nozzle to 0.3mm .... problems!
September 02, 2012 04:18AM

Slow down your printing speed if you have not already done so. If the speed is the same as with 0.5 nozzle you may be going too fast for the 0.3 nozzle. Remember there will be much more pressure in your extruder with 0.3 if the printing speed is the same as before.

Re: Change from 0.5mm nozzle to 0.3mm .... problems!
September 02, 2012 04:55AM
Thank you Jan but I have tried slowing things down and I suspect that this is part if not all of the problem. I believe that with a lower feed speed the filament is spending too much time in the hot end and consequently getting soft where it shouldn't, distorting and then getting wedged so that the extruder cannot do its job. This results in me having to stop the job, dismantle the Bowden tube and then free the blobby filament before having another go with some other change to my settings.
I am going to start playing around with temperatures next in order to see if lowering the hot end temperature will improve things.

Thanks again for your post,

Edited 1 time(s). Last edit at 09/02/2012 05:37AM by Alzibiff.
Re: Change from 0.5mm nozzle to 0.3mm .... problems!
September 02, 2012 05:12PM
That's a common symptom of thermal barrier not getting enough cooling.
Add a fan and point it at the thermal barrier of your hot-end.

The behaviour you've described is actually quite common for some hot-end designs (J-head, Arcol.hu), even with an 0.5mm nozzle.
Re: Change from 0.5mm nozzle to 0.3mm .... problems!
September 03, 2012 05:48PM
Thank you guys. The lack of a thermal barrier was indeed the problem which I have now sorted.
For those familiar with the ReprapPro Huxley hot end which uses a Bowden tube to transport filament from the extruder motor into an arrangement which includes an aluminium heatsink, stainless steel barrel and aluminium heating block it finally dawned on me that when I assembled the hot end and its 0.3mm nozzle, I screwed the aluminium heatsink block too far down the barrel of the stainless steel component which is designed to act as a thermal barrier. All fitted well together in a mechanical sense but there was not enough of the stainless steel barrel between the heat block and the heat sink. This was cured by rotating the heatsink block through a full turn and then reconnecting the Bowden tube connector (which went into the heatsink one full turn more than it had done before).

I have now completed a print which took around 2 hours without the filament above the heater block getting hot enough to deform, distort and wedge itself into places where it shouldn't.

I have learned a lot from the above posts and from my mistake which I guess is how it should be - this experience reinforces the fact that filament needs to heat up in one place only - in the heater block as it emerges from the stainless steel barrel and into the brass nozzle. If it heats up too much in advance of getting that far it it liable to block things up and prevent the extruder motor pushing the filament through. Hey ho - now to sort out my other 0.3mm nozzle settings in Slic3r and still looking for advice!

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