Okay so after trying the new Creality Spider all-metal hotend, I still had the same issue. I decided to try heating the thing to 240C for PLA since the heat creep shouldn't be much of a problem, and the issue went away! I think maybe the PLA absorbed water and required higher printing temps as a result, but I'm also very suspicious of the fact that the same exact filament would produce gorgeous prints at 195C and now requires 235+C to even get out of the nozzle. Speaking of which, here is a comparison between one of the times the printer decided to work at 195 with the stock hotend (maybe this was when I opened a new spool??? I really don't think so but I can't be sure.) vs. now having to print at 240C. Note: these were printed with IDENTICAL gcode that I only modified the temperature for. Also note: I didn't even notice the underextrusion (not part-ruining underextrusion, I think someone had convinced me to turn flow down to 95% for no good reason) on the nice cube until taking these close-ups!
p.s. Sorry in advance for my absolutely fucked up nails, it's been a rough start to the semester and I haven't had the time to care for them.Edited by mcmuffin6o
added bottom photos
My story is similar. The stock hot end on my Ender 3 Pro was fine for about 6 months of heavy use, and then bingo, constant clogging at the gap between the hot end and the bowden tube resulting in under-extrusion. I found a coat hanger that was the right diameter, cut off a piece, and I'd dismantle the hot end and shove the coat hanger down through it. It always pushed out a plug of plastic that should not have been there.
That plug was causing a restriction in the flow. My best guess was that the friction it was causing was the problem. The extruder did not miss steps but my prints were a spider web.
So I bought a direct replacement hot end that was a clone of the stock hot end. I did the Auto-Tune and adjusted the PID and then 2 or 3 hours into a print - under-extrusion. This happened every time. I had changed the bowden fittings to the fancy ones from McMaster Carr. The tube itself is a Capricorn. The extruder is fine.
I came up with this saying: "When you clone a POS you should not be surprised the clone is also a POS."
So now I have an all-metal hot end, a 4015 ball bearing fan blowing on it, a baffle inside the hot end cover to aim the air at the heat sink, and two 10mm holes drilled into the backplate to let the air out. The problem has been fixed and the machine prints as it should. A speed test shows it can put down plastic without a problem up to 175mm/sec with a .4 nozzle. It isn't maintenance free and every 30 to 40 hours of printing I pull the bowden out of the hot end and trim it back 5 or 6mm, clean the nozzle (although I don't believe I've ever had a "clogged nozzle") and run that same piece of coat hanger through the heat sink and heat break. It always pushes out a piece of plastic but it is greatly reduced from what used to be there. I finished an 8 hour print yesterday and it came out beautifully.
To answer your question regarding small nozzles, the answer is NO. Because of the Fluid Dynamics of the flowing plastic, there is a lot more back pressure with a .2 nozzle compared to a .4 nozzle. The same is true if you compare a .4 to a .6 or .8.
The material clings to the inside wall of the brass and there is a transition zone between the material that is stuck to the wall and is barely moving, to the material in the center core of an extrusion that is moving right along. That transition zone is always the same thickness but on a percentage basis, it is a much higher percentage of a .2 than it is of a .8. We see the same issue in air flow through a carburetor or water through a fire hose (both of which I am intimately familiar with).
"All-Metal hot end". The nozzle size doesn't matter, but print speed does so if you want to print with a .2 nozzle you have to slow down. The E-steps must be calibrated. Yes, the hot end needs to be near operating temp when you change nozzles. You can try to push the print temperature in an effort to maintain print speed, but it's a band-aid fix and can have it's own side effects.
It prints so well that I decided I deserved a beer and a cigar (the bracket is an IPod mount for my motorcycle). The baffle on the hot end keeps strings out of the blades. Go ahead and zoom in. You won't find many errors.
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Christ, okay. You really went turbo on the thing. Weird that I could never find plastic between bowden and nozzle when I took apart the hotend to look for such things. There's a lot of good advice in your post, and hopefully it will allow me to get more consistent results.
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