Apparently unsolvable underextrusion!?  

RE: Apparently unsolvable underextrusion!?

That stepped heatbreak works, IF you keep retractions to the bare minimum, I print with no more than 0.5mm retraction, but for this to work the filament has to be dry else oozing occurs with stringing and even 2mm retraction wont eliminate it. Except for TPU, I haven't really used this much so not got optimum settings yet.

When I see people post retraction distances of 5mm! or more, you just know they are going to have problems, molten filament plus moist filament can cause a buildup of pressure which will force the molten filament up into the cavity where the heatbreak opens up.

Although I have as of last week replaced my heatbreak with a non stepped titanium heatbreak and so far the biggest difference is cold pulls, where I used to have to positively tug the filament out, it now almost slides out.

RE: Apparently unsolvable underextrusion!?

I had to replace and toss my nozzle multiple times.  

RE: Apparently unsolvable underextrusion!?

Posted by: @chocki

That stepped heatbreak works, IF you keep retractions to the bare minimum, I print with no more than 0.5mm retraction, but for this to work the filament has to be dry else oozing occurs with stringing and even 2mm retraction wont eliminate it. Except for TPU, I haven't really used this much so not got optimum settings yet.

I think that's a key point. I spent a lot of time working on stringing and retraction and finally found that tuning my extrusion multiplier for each filament made a big difference. I'm able to get by with 0.2-0.4mm retraction, 0.4mm z-lift and no wiping for most prints.

When I see people post retraction distances of 5mm! or more, you just know they are going to have problems, molten filament plus moist filament can cause a buildup of pressure which will force the molten filament up into the cavity where the heatbreak opens up.

I suspect a lot of people start researching the issue and wind up trying solutions meant for other printers. With the E3D direct drive hotend, you should never retract more than 2mm or you wind up pulling molten filament up past the transition zone. That would certainly explain a lot of the "2.2mm blobs" we see!

Although I have as of last week replaced my heatbreak with a non stepped titanium heatbreak and so far the biggest difference is cold pulls, where I used to have to positively tug the filament out, it now almost slides out.

Did a similar swap myself. Can't say it's improved anything, but since I was going to be tearing my hotend apart, I figured I'd get ahead of the game. It's nice starting with a fresh clean block as well. My first was pretty gunked up from my early learning.

RE: Apparently unsolvable underextrusion!?

Posted by: @charles-h13

I had to replace and toss my nozzle multiple times.  

Heh. Yup. Early in my fine stringing battles, I swapped nozzles and was amazed at what an improvement it made. I think my original was damaged from my early clumsy attempts at clearing blockages with the needle. I no longer use the needle since figuring cold pulls out. It's hard to accept that nozzles are consumables, but keeping a few spares on hand is definitely a good idea.