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ciclopez

New hotend: Underextrusion and stringing

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Hi,

I recently bought a new Ultimaker hotend (nozzle, heater block and brass pipe) because I ruined the last one trying to unclog it. Now I'm having problems with this new hotend. Now I need to print at 230ºC for a 30-40mm/s speed because otherwise it underextrudes (I used to print at 210ºC or less for this speeds) I thought this was the origin of the stringing issue, but lowering the temp doesn't help. I tried with different retraction speeds and objects with almost no retraction but everything is the same.

 

I think this video I made is self explanatory:

 

 

Any help would be appreciated.

Thanks!

 

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Wow! Nice video. Lots of information packed into 3 minutes 46 seconds.

For the most part you have things working pretty well. And you are trying the correct things (slower speeds, lower temps) to reduce stringing. And your stringing is everywhere but the strings are quite thin - I've seen worse but I've also been able to get it to zero if I try hard enough. I suspect the strings you *do* have will come off very easily and cleanly. I think you are close enough that if you just try a different manufacturer's filament you might be able to get it to zero stringing.

Also fan is important for that pyramid. Each post doesn't have much time to cool with almost constant contact to a hot nozzle so it's extra hard to stop stringing. Was your fan on during the pyramid support printing?

When retraction occurs, look at the top of the arc of the bowden tube. Make sure the filament goes from touching the top of the tube, to the bottom of the tube at full retraction. If not increase your retraction by .5mm. My retraction is at 4.5mm and that is about perfect. If you retract too much you get air in the print head which alternately causes first over and then under-extrusion.

One thing that I definitely saw was a problem was your first layer. You have a shot where you printed only the first layer of several complicated shapes and in the video there are some holes which you might think is "under-extrusion" but in fact is just bad leveling. You need to press the first layer down into the tape a little better. So raise your bed by about .1mm and try that first layer again (.1mm is about the thickness of a piece of paper).

Here is a photo of how the first layer should look (look at the skirts):

gallery_4795_203_296761.jpg

 

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Thanks for your response.

The strange thing is that with my previous nozzle and the same filament (Ultimaker filament) I never had this problems, the retraction was working perfectly at 4.5mm and 50mm/s and the extruded material was smooth at 210ºC and 40mm/s. I don't want to remove all the stringing every time I print something. The software is the same, the version is the same, the firmware is the same... the nozzle is the only thing I changed. Could it be that there is something wrong with this nozzle?

You are right with the bed leveling, when I printed that objects it was a bit offset, but in the pyramid example there is underextrusion if I go lower than 230ºC, do you need that temps to extrude correctly at 30-40mm/s?

Anyway, I'll try with more retraction distance and post the results.

 

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example there is underextrusion if I go lower than 230ºC, do you need that temps to extrude correctly at 30-40mm/s?

 

I didn't exactly see underextrusion in your video. On the side walls it should look like the second photo (the black and white one):

http://umforum.ultimaker.com/index.php?/topic/1872-some-calibration-photographs/

But to answer your question:

I can print 150mm/sec at 230C without even a hint of underextrusion (as shown in photo with purple cube) but if I go down to 210C I *will* start to see some and can even cause the filament to grind ruining the print.

At 40mm/sec I can go down to 190C fine.

So if you are truly seeing underextrusion (and I wasn't able to see any in any of your video) then you should test your extruder to make sure it can pull 22 pounds on the filament by hanging a weight on the filament and not feeding it thorugh the tube. If that is working then test:

1) filament diameter - if it gets over 3mm it can get stuck in the bowden

2) hot end temp - you already did this in your video

3) nozzle obstruction. look at the tip with a magnifying glass. Consider removing the nozzle and cleaning it out with a hot wire taken from a metal brush. Put both the metal wire and the nozzle in a gas flame before pushing the wire in the end and pulling out the other side. Make sure you can see light thorugh the hole.

 

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