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Severe under-extrusion part-way through print - any ideas?

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Hi, I've been trying to print a fairly large part for a few weeks now. I started with ColorFabb XT, then tried ColorFabb nGen and finally ColorFabb PLA/PHA. All have suffered from under-extrusion and. at least with the nGen, warping so bad as to make the part unusable (except that it was unusable anyway due to the under-extrusion). The machine is an Ultimaker 2 with Olsson block.

During the switch to PLA/PHA I also switched to a brand-new 0,4 mm stainless steel nozzle (I didn't have a brass one) and changed the teflon hot-end isolator for a new one.


nozzle: 0.4 mm stainless steel

temperature: 210 degrees

layer height 0.2 mm

speed: 40 mm/s

fan: 100%

infill: 100%

The object has walls and base 2.4 mm thick. It started OK, including the soldi base and about the first 1 cm of walls. Then it started to show under-extrusion. I tuned the temperature up and down 5 degrees, material flow to 110% and 100% and speed to 80%. However, none of these helped. The majority of the print is completely porous and flexible. Images below.

Any ideas?







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I don't think so. (1) I was careful with retraction to avoid this problem; (2) I've checked the filament itself and found no problem of "eating".

Reading some other posts I tried reducing the temperature to 195 degrees. Using the "Move filament" control I got nice strings of filament out of the nozzle. See the picture. Using a calliper I measured this at between 0.32 and 0.56 mm diameter. So it seems to flow OK at this temperature.


So I had another go at the print. This is what I found:


And here is a detail:


After this I looked at the filament driver (the entrainure) and, following a video on the Ultimaker site, reduced the tension (white indicator to the highest position), though, to be honest, there was no obvious change.

Then I modified the temperature again, to 200 degrees. Watching the machine it seemed OK for the first 10 minutes. Then it started showing signs of under-extrusion again, so I increased the temperature to 205 degrees. It got better, but after leaving it for a while I returned to find this:


Obviously I've aborted the print now and I've given up. It's looking like I can't print anything now, at least with this nozzle. As I said, it was a new one. More accurately, it was an unused 3dSolex one bought 2 years ago.

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First of all at 40mm/sec and .2mm layers you shouldn't be going below 225C. That's pretty high volume for a 0.4mm nozzle. You can just barely achieve that at 200C but you will get some mild underextrusion on even a brand new printer with a brass nozzle.

With a steel nozzle though you need to go another 5C hotter so I wouldn't go below 230C (steel doesn't transmit heat as well so it will be cooler than the block).

But I ahve to agree you do have some issues with your printer. I'm pretty sure you can print just fine at 20mm/sec and 225C but if you want to print at the speeds you used to print at then you are going to have to fix this printer. I would look at the list that neotko sent you but most likely it's the teflon part so I would start with that.

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